Newtons blob
Posted on 4 February 2012 at 15:24h
I was searching E bay for some interesting items when I cam across this Newtons rings apparatus from Philip Harris. It's exactly the same as the one that we had when I was at school, coming over all nostalgic I decided to put in a bid and won it. I don't have a travelling microscope (although there is one for sale on Ebay for £100) but was wondering if I could do a digital version with my camera (phone). I set it up in the lab and although I could see the rings with my naked eye my ettempts to take a photo failed. I was hoping to analyse the photo with loggerpro which would be quite neat. The biology department have a video attachment for a microscope so might try with that. At least it can't be worse than my attempt which is more like Newtons blob than his rings.
The problem seemed to be too much light in the area of the rings but I'm no photographer so it could be something else. If all else fails its a nice ornament and looks great on my bookshelf.
DIY
Posted on 1 February 2012 at 16:50h
When things break I don't tend to have time to repair them and since we don't have a lab technician I simply put the broken stuff in a box and buy a new one. Today I felt inspired so decided to have a look in the broken things box and to see if I could fix anything. Over the years I have had several Pasco photogates stop working so there were 3 in the box. Since they were broken there was nothing to lose so cracked one open to have a look. Loose wires is as far as my trouble shooting goes and nothing was loose so that was that. I remembered that before they stopped working they worked for a while if the cable was tied down so I reckoned that the cable was the problem. On closer inspection I found that the cable clamp was very tight and could be the problem so I cut the squashed part out, soldered the bits untidily together, stuck it together with duct tape and now I have 3 extra photogates. The moral of the story being, never throw anything away.
Challenging the laws of nature
Posted on 1 February 2012 at 12:29h
I like my shoes to last at least one year. This has caused me some problems the past couple of months because bought a pair or rubber boots that had been in storage for some time and they started to deteriorate after only 6 months wear. So I've been walking around with holes in my boots for some time. That's OK when the ground is frozen but not when it melts. I should point out that in Norway we wear rubber boots almost every day because it rains so often. So, I reckon that I've now had the offending items for about a year so I bought some new ones. As you can see they're made for Vikings so should be strong enough. The boots came with a little booklet of information with the motto "challenging the laws of nature since 1920". One of the pages was about the new rubber compound that is 30% ligher than traditional rubber. The info goes on to say. "That means if you walk 10km , your feet will have lifted around 315kg less than wearing traditional boots". That means that traditional boots must weigh 1050kg!
What they are of course meaning is that you must lift an extra 315g 1000 times or something like that. I just weighed a boot and it's 1kg so a 30% saving in weight is around about 300g. Each step is approximately 1m that's 10,000 steps in 10km so you'd have to lift each boot 10,000. How do they get 315kg?
I think I will go to the training room this evening and lift 10kg, 100 times then tell everyone tomorrow that I lifted 315kg.
Bouncy sausage
Posted on 30 January 2012 at 10:21h
Last weekend I took the four students in the photo on a surfing trip. January surfing in Norway might sound like a strange thing to do but I can assure you it's not strange at all, cold yes but strange no. Over the Christmas period the West coast of Norway was hit by storm Dagmar which caused a lot of trees to fall down and some unusual stuff to get washed up on the beach, including the inflated sausage thing in the photo. It was probably some sort of fender from a ship but now, as you'll see in the video, it's a bouncy castle.
Lots of interesting physics here. The two on the left (Oliver and Rafik) seem to have hit the right frequency and are bouncing nicely in phase but Nikola experiments with different frequencies and phase relationships.
This wasn't the only sausage of the weekend, we also ate three packets of chicken sausages which also presented some interesting physical problems including how to roll a sausage that has been bent to fit into the pan. Maybe I'll take that one up again later.
Another failure
Posted on 24 January 2012 at 18:11h
This morning I wrote a problem sheet for my HL students on the photoelectric effect. The first question was about a filament lamp so I illustrated it with a photo of the lamp behind my head. I was interested to notice how the brightness of the lampshade changed from the inside to the outside and wondered if I could use the photo to show that the intensity was proportional to 1/r2 . A couple of months ago I wrote a blog post about using Paint.NET to measure albedo so thought I'd try the same technique.
I realised that because of the angle of the shade relative to the camera I needed to place a scale in the lamp. You can see I used a piece of mecano, the holes are clearly seen at regular intervals. then sampled the photo and plotted a graph of position against intensity (units unknown).
You can see the trend is in the right direction but its hardly a 1/r2 curve. I think I would have to calibrate the intensity measurement and do something about those stripes. The shape of the shade might also have some influence. Maybe I'll try this with a bulb in the middle of the floor. On the other hand maybe not.
One pamph two pamphs
Posted on 23 January 2012 at 13:26h
Today I was introducing single slit diffraction to my SL class and was having difficulty showing how the phase changed as you increased the diffracting angle. I was trying to do it on the SMART board and could get an infinite number of wavelets by cloning one of them but couldn't get them to rotate in the right way to show how the phase changed. I managed to solve the problem at home using interactive physics to give the animation here. A couple of posts ago I wrote about how I was going to be more thorough when introducing new terms to my class. Today's term was "wavelet". Many students, especially native English speakers, were unsure if this was a proper word. One commented that it must be since it's in the text book (hmm). I assured them that putting let on the end of a word just makes it a small one. Like pig and piglet, book and booklet, leaf and leaflet, pamph and pamphlet. Oh dear.
Being negative for the sake of it
Posted on 22 January 2012 at 14:25h
The other day in class I was deriving the equation for the simple pendulum and started wondering how to make the solution negative. I knew it had to be to fit in with the result a= -ω2x but why should the component of mg be -ve? I looked the derivation up in several places but wasn't satisfied. Most sources used a similar approach to hyperphysics. That the force is -ve because it is but to my mind -mgsinθ is simply in the opposite direction to mgsinθ so that doesn't make sense.
I asked one of the maths teachers and he agreed that you can't simply say that the Force is -ve because of the direction so at least I realised that I wasn't missing something obvious. The only sensible way I could think of introducing a -ve was after substituting sinθ=x/L x is the displacement so if this is to the right then F is to the left so must be opposite sign.
Eventually I found an explanation for the early introduction of the -ve sign that I am happy with. It comes from considering the angular motion of the pendulum. τ = Iα Now the torque is in the opposite direction to increasing θ so τ = -LFsinθ which makes sense. Cancel out a few things and you arrive at F=-mgsinθ. No good for our students though who don't study rotational dynamics. Roll on the new syllabus.
Steve Sque, University of Exeter
And if it's any consolation that animated pendulum made me feel sick too.
Win some lose some
Posted on 21 January 2012 at 16:18h
Some time ago I thought of doing a design lab using rubber powered model planes, however it seemed a bit extravagant to buy model planes at £5 each when all I wanted was the motor, so I set about looking for an alternative. My first thought was to make make a rubber motor with a wide glass tube. Stretch the rubber inside and use it to turn a pencil which is attached to the end. I'd draw a diagram but there's no pint because it didn't work anyway. Whilst looking through the drawers in the chemistry lab (before I got caught) I did find a big store of glass tubing which I'm sure I can use for something else. The problem was that there was too much friction between the glass tube and the pencil so I came up with the solution to put the pencil in the middle of the elastic band stretched across an ice cream carton. In the example shown have replaced the pencil with a metal strip. This makes it possible to attach magnets to increase the mass of the system. I can think of loads of possible research questions related to this so I'm going to try it with my class. To add to the possibilities I have also bought a big box of assorted rubber bands.
Subscribing teachers will find some research question ideas here, students will have to work out their own.
After playing with this I turned my attention to a new SH lab using the classic floating cylinder example. This is not as easy as it first seems. First you have to find a cylinder that you can make float by adding masses. I tried a drinking straw and plasticine. The damping on this was so big that it only did about half a cycle but that was OK, I'd keep it going with my hand and the students would learn about resonance at the same time. So I started changing the mass but got no measurable change in frequency. The frequency is proportional to √1/m so a small change in m has little effect. I tried a test tube, (chemistry lab bottom draw right hand side) but to make it float upright needed so much mass that it sank. My best effort was with a plastic tube with steel balls in it, however I still didn't measure a difference in f between the two extreme values of m. I think this might work on a big scale but will have to wait until the summer so we can use the fjord which is a bit deeper than my bucket.
LILAC
Posted on 19 January 2012 at 16:10h
LILAC stands for language in Learning Across the Curriculum. Last term teachers at my school were offered the chance to take this course. I thought it would be a good idea to increase my awareness and gain some ideas so signed up. In my school most of the students do not speak English as their first language and although most have a good command some struggle. I have often noticed that even students with a strong background in physics can have diffficulty when it comes to understanding exam questions and often perform well below their potential. In physics classes we are very good at defining the words that we want our students to use (displacement, velocity, acceleration etc.) but not so good at giving examples of how to use them. I am absolutely not the person to try to teach anyone grammar but I am going to start to giving my stuents examples of how to put some of these terms into sentences.
A body experiences a constant force resulting in an acceleration.
A car travelling at constant velocity of 5ms-1 accelerates to 10ms-1 in 5s.
Hmm. How can a car travelling at a constant velocity accelerate? What in the sentence says that the car is no longer travelling at a constant velocity but is starting to accelerate? I can see that I could very easily start to tie myself into linguistic knots.
Undeterred I will start by adding sentences to the vocabulary lists on my scheme of work pages.
I might even try the odd word game with my class. (Steady on now)
Divers watch
Posted on 18 January 2012 at 12:42h
Last week my son went diving with one of the teachers from the college, I went to watch which wasn't very interesting since all I could see were bubbles coming to the surface. Occasional excitement was induced when the bubbles stopped for a few seconds but that sort of excitement I could do without. As I watched the bubbles moving around the fjord I noticed that sometimes they were complete spheres but at other times in the form of many small bubbles. have no idea why this is and to find out I'd have to get under water with them and I'm not doing that. I think I've got reverse fear of heights. I get scared when I see the surface of the water getting higher and higher. After the dive I asked them about all the bubbles and was interested to learn a bit about the role of the BCD (buoyancy control device). This looks like a life jacket and has a similar function. Because of the weight of the air tank the diver would sink so to compensate for this they put air into the BCD. To go down they release air. As they dive deeper the air in the BCD becomes compressed so has less volume therefore the up thrust is less so to keep the forces balanced they have to add air. On the way up the air expands etc. so they have to release air to rise at a constant rate. The same thing happens to the air in your lungs. If you breath in air at depth it will be at high pressure and will expand as you rise to the surface. If you hold your breath whilst doing this your lungs would explode. Charming.
A bit more about bouyancy from Jelena (the diving biology teacher).
Late Christmas present
Posted on 16 January 2012 at 12:22h
Just before Christmas I made a blog post about a small solar car that I bought as a stocking filler for my son. I tried it out and decided to buy a whole bunch of them for my class. I also bought some lamps, plug in dimmers and power meters. Today I tried it out with my SL class and they had no trouble thinking of several interesting research questions. None of them have finished the analysis yet (it was only 2 hours ago) but it looked like they were getting some consistent results. With out giving the game away there are a lot of variations in both independent and dependent variable. In the photo you can see the power meter piggy backed on the dimmer, worked quite well.
Arc Attack
Posted on 15 January 2012 at 13:01h
I just switched on the TV and caught a glimpse of Americas Got Talent. The act being auditioned said they combined science and rock music. Quite a show as one of the band stood between two Tesla coils at 500,000V each and got zapped. He was wearing a metal suit so that his body so there would have been no PD across him but I certainly wouldn't have done it, I wouldn't like to be one of the other band members either. On the screen shot you can see that there is a gap after the coil before the lightning starts, why is that?
I have done a bit of web research and have found out that the gap is not always present. Often there is a straight part of the spark before the branching bit. Seems to be something to do with the very high field close to the top of the Tesla coil. I've an excellent explanation of how a Tesla coil works here Tesla's Legacy. Some nice physics.
Increase in empathy
Posted on 12 January 2012 at 16:05h
Today the electricity was switched off at school so that a new fibre optic cable could be strung from the pylons. Most of the teachers decided to carry on as normal to show their students what it must be like in countries with no electricity. I decided to show my students what it’s like in countries with no school.
Even before the power went off at exactly 10 am we had some mini power cuts of our own in the physics department. We were doing the specific heat capacity with a kettle lab and the circuit breaker kept tripping every time all 9 kettles were switched on at the same time. I knew there had to be a reason why the lab was only supposed to hold 16 students. I always thought it was just the number of chairs.
Sweating makes you cool
Posted on 10 January 2012 at 17:39h
Do you ever tell your class something and then think “that was a load of nonsense”. Today I told them that sweating makes you cool but it doesn’t really does it, well not in that sense at least. I once said you can’t see light when it’s actually the only thing you can see. What I meant was that you can’t see that light is a wave in the same way as you can see a water wave but that’s not how it came across. The sweating example is of course about losing heat rather than being cool. Whilst on the subject I once had quite a cool car, well I thought it was cool at least and I built it myself so that has to add some coolness points. It was a Spartan kit car based on a triumph spitfire. On the surface it was brand new but underneath was a scrap heap. One summer day I was driving along and realised there was a strong smell of petrol so after a couple of miles I pulled in and had a look under the bonnet to be surprised to find an icicle hanging there. What had happened was that the petrol pipe had sprung a leak and started squirting petrol everywhere, this vaporised causing the surrounding area to cool down. Water condensed on the cold area and turned to ice.
Time
Posted on 9 January 2012 at 11:32h
First day back at school and having to get used to getting up in the dark again. Thankfully this doesn't last forever as the days get longer at an ever increasing rate so soon we'll be getting more sun than you Southerners. A couple of weeks a go I saw a comment on facebook related to the apparent fact that soon after the shortest day on December 22nd the mornings don't get any later at all it's only the sunset that gets later, the sunrise actually doesn't start getting earlier than the shortest day until January 4th. You can see all the details here time and date .com
I put January and February into excel and plotted the sunrise and sunset and you can see it's not symmetric. The reason for this is the difference between the solar time and the clock time. Solar time is based on the position of the sun but because the sun moves in an elipse it moves slower when it is far from the sun that when it is close (conservation of energy). Clocks tick regularly so as the earth speeds up the solar clock ticks faster but slower when the earth slows down. So this makes the time of day when the sun is at its highest slightly different each day. Today's clocks are based on a standard second but many years ago they were based on the movement of the earth around the sun however since the speed changes the time had to be adjusted using the equation of time. Quite interesting.
Faradays Paradox
Posted on 3 January 2012 at 12:45h
Yesterday I was writing some problems on electromagnetic induction so my students would have something to do when they get back after the holiday. There are a couple of classic HL situations, the wire moving on rails is the simplest and then there’s the rotating disc. There are some variations on the theme but the classic Faraday’s disc is a disc rotating in a uniform field. At first it might appear that there should be no EMF since there is no change of field covered by the disc however if you consider a radius then it is sweeping through the field like straight wire.
Now it gets odd, if the magnet is rotated then one would expect there to be a current but there isn’t. Curiouser and curiouser, if the magnet and disc are rotated together then there is a current, how do you explain that. It caused Faraday a headache too hence the title “Faraday’s paradox”. The simplest way to explain this is that you have to think about the whole circuit not just the disc. Firstly the field lines are not just passing through the disc they will pass through the connecting wires too, If the magnet is rotated EMF is induced in both the disc and the connecting wire, these EMFs oppose each other so no current.
If the disc and magnet are rotated then there will be induced EMF in the connecting wire only.
If it works as a generator then it must work as a motor.
Veritasium
Posted on 2 January 2012 at 12:47h
The other day I was sent a link to this interesting website - Veritasium. There is some great stuff here. My students have done a lot of experiments with slinkies so I was particularly interested in the slinky drop experiments. I like the explanation about the wave travelling at the same speed as the end of the slinky but couldn't quite tie it in with Hooks law. If the ball is at rest then the tension = the weight but as the spring gets shorter the tension must get less. I tried simulating this in interactive physics by placing two springs between 3 balls but it didn't work. I also copied the video into logger pro and found that the top accelerates at a little faster then g. The middle seems to accelerate at much less then g but I only had a few frames to analyse so won't dwell on that. After a lot of playing around it suddenly all made sense. I was making the mistake of looking at the tension in the whole spring but I should have just considered the bottom coil. The separation of the last two coils is constant until the top comes down to meet it, the tension is related to the coil separation so will also be constant.
After further experimentation this time with Algodoo I made a working simulation.
Notice how the last section doesn't change length until the compression wave gets to the bottom. I also sent a wave down the slinky without cutting it. The time for the wave to get down the slinky is about the same as the time for the top of the slinky to drop.
Excellent waves
Posted on 30 December 2011 at 17:18h
Today I was preparing some material for my next workshop in Berlin and thought I'd play around with using excel for simulating physical phenomena. It's not my favourite tool but I managed to make this neat simulation of two waves adding to produce a standing wave. Took me ages to work out how to animate it but found a very simple way in the end.
Subscribers get access to this page of instructions for use with or without students.
Kaluza Klein
Posted on 30 December 2011 at 12:08h
I've just finished reading Johnny Dawes autobiography "Full of Myself". Johnny was a rock climber who did things a bit differently to the rest of the crowd, when everyone was into bolts and competition he stuck to tradition and adventure. Johnny is very much into analysing the way he moves on rock and tarmac, so he knows a lot about friction and gravity. One of his climbs is called Kaluza Klein, the theory that tried to unify the forces of gravity and electromagnetism very apt since Johnny uses the electromagnetic force between the molecules of his shoes and the rock to overcome gravity. Johnny is a very fluid climber. in fact he doesn't really climb he scampers, moving from hold to hold without stopping. In the book he talks about using momentum. A rock climb is basically a line of holds some of them big enough to hang on with one hand others not, the idea is to apply enough downward force on the holds to project oneself upwards with enough velocity to reach the next. If you can catch the second hold on the way up then you don't have to apply so much force to hold onto it.
The video below shows this nicely on a few occasions, pulling with both hands catching the next hold with one. Apologies to any Czech viewers as I'm sure Adam uses a couple of rude words when he falls off.
ADAM ONDRA - FIRST 8C BOULDERS from BERNARTWOOD on Vimeo.
Keep your distance
Posted on 11 December 2011 at 11:16h
Yesterday I had my bi-annual hair cut and was surprised by the amount of grey hair that landed in my lap. I had been under the impression that the amount of grey was actually getting less but when seen close up this doesn't seem to be the case. It's all to do with resolution. When I normally see my own hair its in a mirror and the only mirror I tend to look in is the one in the bathroom which means I'll be about 2m from my image. The diameter of a human hair is about 10-4 m so the angle subtended at 2m = 5 x 10-5 rad Taking the pupil diameter to be about 5mm and the wavelength of light 600nm the minimum resolvable angle will be 1.22λ/d = 1.5 x 10-4 rad so the grey hair won't be resolvable. Reduce the distance to 40cm and the angle is 2.5 x 10 -4rad which will be resolved. Of course diffraction isn't the only effect that needs to be considered here, my poor eyesight also has something to do with it. As you get older your hair gets greyer but your eyesight gets worse preventing you from seeing it. Neat.
By the way, after my hair cut I bought one of those smart phones hence the improved resolution of my photos.
Paper 3 May 2011 tz2
Posted on 9 December 2011 at 10:51h
I'm on holiday which means I've got time to work my way through the past exam papers that I've been hoping would solve themselves. I know that the mark schemes are available from the Ib and I'm not trying to provide an alternative to that, you should still get these and use them for marking trial exams etc. However when students are using the exam papers for revision they often require a fuller explanation than is given on the mark scheme. I do the papers on my tablet PC using journal then I take screen shots of the pages, crop them using paint.NET and save them as .png files which I upload to the web server where I they are displayed on a web page (example). I hide the images to make the page easier to navigate. Takes a bit of time but when it's done it's done.
So I'm fresh from from uploading the solutions to may 2011 paper 3 time zone 2. Subscribers can get it here. Fresh from doing the whole paper I have some general comments.
- some of the questions are incredibly long, particularly the communications
- the questions are no where near of equal difficulty, the particles and relativity questions are way harder than the medical
- I think a good student would score well on medical without even doing the course
- students have to memorise the properties of particles
- sometimes its difficult to see how the marks are awarded
- doing past papers is a good way to know what is required
iPhone ripple tank
Posted on 7 December 2011 at 15:34h
I've been a big fan of Paul Falstad's applets for a long time and particularly like his ripple tank. His home page has a picture of him with a small child (presumably his). The other day I was commenting in class about how this photo has always been on the site and was wondering how old the child is now. Anyway, as I flashed past the home page something caught my eye, iPhone / iPad and android apps. The ripple tank is now available for the iPhone, pity I haven't got one.
Stocking filler
Posted on 6 December 2011 at 13:20h
I hope my children don't read this blog because one of them is going to get this little car in their Christmas stocking. Well they aren't exactly children any more but they still like surprises. It's advertised as "The Worlds Smallest Mini Solar Powered Robot Racing Car Toy Gadget Cool". I just received one in the post and it really works and not just in sunlight but also if placed under a spot lamp. I thought this would make a great subject for a design lab so I'm going to order a whole bunch of them and a class set of spotlamps.
They're dead cheap and can be ordered from Ebay.
More details for subscribers Solar powered car
Flat screen detective
Posted on 5 December 2011 at 12:16h
It's sad but true that the other night I was sat watching the blank screen on our flat screen LCD TV. What I noticed was that light reflected off the blank screen was being diffracted so took a photo of it.
I was interested to know what was causing this affect, my guess was that the pixels were diffracting the light but were they small enough to cause such an apparently large angle of diffraction. To find out I took some rough measurements.
I was sitting about 3m from the TV and with my arm outstretched measured that the first two maxima to be 2cm apart. So diffracting angle for 1st order = 0.01/3.
For a diffraction grating dsinθ = mλ where m is the order (1)
Taking λ = 600nm gives a value of 0.18mm which is about the size of a pixel.
The second problem was the angle between the two diffraction patterns. Rows of horizontal pixels would give horizontal and vertical patterns. So, in true Sherlock Holmes style I magnified the screen with my magnifying glass. This is what I saw
Elementary my dear Watson.
Wellington's sock
Posted on 2 December 2011 at 08:12h
I've just got back from taking my dog for his morning walk up the hill behind my house. The ground was wet so I wore my rubber boots (Wellingtons to Brits). As anyone who wears these boots regularly (or remembers wearing them as a child) will know, as you walk up hill your socks slip off your feet. This doesn't always happen though, it depends what sort of socks you wear. Today my left sock came almost completely off but my right one stayed on. What caught my attention though was that on the way down my left sock climbed back up my foot and was completely in place by the time I got home. I don't remember that happening ever before.
It's all to do with the relative frictional force between the different surfaces. The friction between the sock and the boot is greater than the sock and foot so the foot moves backwards relative to the sock, as shown in the animation.
Springbox
Posted on 29 November 2011 at 15:38h
I have been doing about thermal physics with my first year classes. I always like to start with showing how thermal energy is connected to energy in mechanics. Push a block along the ground at a constant velocity, work is done but where is all the energy going etc.
So the energy is going to increase the internal energy of the ground and block but how is the energy distributed? This is what one of my students asked me after class today. It must be something to do with the atomic structure in the two surfaces but that's as far as I got so I tried to make a simple model of the situation by thinking about the collision between two pairs of blocks connected by springs.
Let's say the blocks are identical but the springs are different. The spring on the right has a k value 10 time the one on the left. When they collide the inner blocks experience an equal and opposite force (conveniently ignoring the outer blocks here). The lighter spring (left) will therefore be compressed 10 times more than the stiff one. Elastic PE = ½kx2 so the left combination takes away more energy from the collision than the right hand one (k is 1/10 but x2 is x100). If we were take this to the extreme and have one spring was totally stiff then it wouldn't take any of the energy.
Light on light off
Posted on 28 November 2011 at 20:13h
Here is a photo of two of my SL students doing some very serious scientific research. The technique is actually quite difficult. They are trying to measure the seperation of spectral lines of a Helium lamp, the problem is if you have the light on you can't see the lines but if you turn it off you can't see the ends of the caliper. I'd definitely go for the light off option it might mean that I can't see the scale but it would also mean that no one could take a photograph of me.
Why cepheids pulsate
Posted on 20 November 2011 at 15:00h
Last week I was doing about cepheid variables with my SL class and we were talking about why they have a changing brightness. The simple explanation is that they are expanding and contracting, if the temperature of the star is constant then this would cause the luminosity and hence the brightness to change. Unfortunately it's not that simple.
Its all to do with the outer layers of the star.
- The core of the star is producing heat which is absorbed by the outer layer causing the outer layer to get hot.
- As the outer layer gets hot it expands and cools.
- The outer layer now absorbs less radiation. This means that more radiation is escaping which results in an increase in brightness.
- As radiation escapes the gas cools. The cooler gas now contracts due to the force of gravity. This causes it to get hot so it absorbs more radiation and the cycle repeats.
The animation shows this although the graph is a bit misleading, I'm not sure why the blue lump moves around. It would make more sense for the curve to be static with a point moving along it. I'm also not sure why the core is changing size.
Why don't all stars do this?
This is because not all stars have an outer layer that absorbs more radiation when it is hot. One way this can happen is if the layer consists of helium. Hot helium is ionised which absorbs light better that cold helium which isn't.
So why does ionised Helium absorb radiation better than non ionised Helium?
Hmm. I would expect it to be the other way around since without electrons to be excited how can the Helium absorb radiation. The answer is that ionised Helium or Plasmas don't absorb radiation in the way that atoms do. A Plasma is a gas made of nuclei and electrons moving rather quickly in random motion. When EM radiation passes through a plasma the charges become excited by the varying Electric field thereby absorbing energy. Normal gaseous Helium on the other hand can only absorb the specific wavelengths that excite atomic electrons.
Here is an alternative explanation
- The outer layers of a star are made of gas.
- If a gas gets hot it expands.
- The outer layers of gas in a stable star stay the same size because the temperature is constant. The radiation entering the layers from the hot core = the radiation leaving
- If a layer becomes too dense it absorbs more radiation leading to an increase in temperature. The gas expands which reduces the density until equilibrium is again established.
- In a Cepheid the dense layers are made of ionised He which gets hot and expands however as it expands the electrons recombine with the ions resulting in a release of energy. This stops the temperature falling so the gas continues to expand until all the He is recombined, then the temperature falls.
- At this point the star is very large so is emitting a lot of radiation (this is the bright part of the cycle). The gas now cools and starts to contract. As this happens the temperature of the He rises again and the atoms again become ionised - the temperature of the gas staying constant allowing the contraction to continue.
Measuring Albedo
Posted on 20 November 2011 at 10:18h
How do you measure Albedo?
Albedo is the ratio of reflected light/ incident light so to measure it one would have to measure these quantities. One way would be to use a light sensor or a light meter but I was wondering if it was possible to get some idea of albedo from a digital photo. After all the photo is simply a record of the reflected light so it should contain all the information. I use the programme paint.NET for manipulating images (it's free) so thought maybe I'd try using this.
Under the windows menu there is the colours option which opens a pallet. Click "more" and you get a display of the amount of Red Green and Blue in the colour as well as the HSV numbers. It is the V number (value) that we are interested in. This is related to the lightness of the colour, which is a measure of the amount of reflected light in a photograph. Under the tool options there is a colour picker that looks like a pipette, this can be used to sample the different areas in a photo. So If you open a photograph in Paint.NET you can get an idea of the amount of light reflected off different areas by sampling the colour and noting the V number. Perfectly white would have a V number of 100, so dividing the V number by 100 gives an idea of the albedo. it doesn't give the actual value since the V number is not proportional to the intensity of the reflected light but it gets the idea across. You have also got to be careful with shadows.
Plum pudding
Posted on 13 November 2011 at 11:08h
It's almost Christmas, well the lights have started to go up and Ikea is selling decorations so it can't be far off. In our household this means it's time for the Christmas pudding ritual to begin. By Christmas pudding I mean the traditional British version also called Plum pudding. Yes, the one made famous by J.J. Thomson. The plum pudding model has -ve plums (electrons) surrounded by the +ve pudding. There are several problems with this model, firstly the plum pudding contains no plums. It has raisins, sultanas, currants even apple but no plums. The fruit that is in the pudding turns into a fairly homogeneous dark brown material that has little resemblance to the Thomson's picture of the atom, a closer resemblance would be a raisin bun or rosiner bolle as we call them in Norway.
When mixing the ingredients for Chritmas pudding it is traditional for all memmbers of the family to make a wish. I wonder what wish Thomson made? Seems like it didn't come true.
Chemistry wins the flint argument
Posted on 3 November 2011 at 13:36h
When I go camping I like to start fires with my "survival professional" flint. Actually what I do is light the gas fire with the flint then light the wood fire with the gas fire so a bit of a cheat really. I was wondering how the flint works to produce sparks so applying simple physics:
Work is done against friction when the flint moves across the blade, this work is converted to heat which melts the iron causing it to glow, simple. But how much work is done and is it enough to melt the little bits of iron? And another thing why do you have to have a special sort of iron?
I guess that the force needed to move the flint is in the region of 1N and the distance moved 1cm so W = 0.01J.
To make the iron glow it would have to be about 1000°C. It's specific heat capacity is 460 Jkg-1K-1 so about 2 x 10-8 kg of iron would be made to glow assuming the iron got all the energy. Density of iron = 7000 kgm-3 so the little bits of iron would have volume of 1.7 x 10-11m3 if the bits a spherical they would have a diameter = 0.3mm. This is a bit big but shows that it's possible.
Unfortunately it's completely wrong.
What actually happens is the freshly ground iron filings spontaneously ignite as they oxidise in the air. So it's nothing to do with work done and friction. That's why you need the special flint. I was begiining to wonder how all the energy managed to get concentrated into the little scrapings of iron.
Wakey wakey
Posted on 2 November 2011 at 20:06h
It's often difficult to keep students awake in class at this time of the year but the wake I'm referring to in the title is the wake behind a boat. I seem to travel on the boat between Bergen and home quite a lot and often notice interesting things. This time it was nice enough weather to go outside so I stood at the back where I got a good view of the trail of foam snaking away from the back of the boat. What interested me was that the foam stayed in a parallel sided stripe where as the wake or wave produced behind the boat spread out. It was a nice demonstration of how its the disturbance in the water that spreads out in a water wave not the water itself.
Another interesting phenomenum in the photo was the rather tatty norwegian flag which was exhibiting several different harmonics as it flapped about in the wind.
Retro fridges
Posted on 30 October 2011 at 12:19h
Earlier this year we bought a new fridge, one of those retro ones. Ever since we had it we have been a bit disappointed because it simply doesn't make the contents cold enough. The other problem is that the switch that turns the fan on when the door is close is not aligned properly so the fan doesn't come, what I hadn't realised was that this switch also turns off the interior light. So if the interior light is always on then maybe its heating the inside of the fridge stopping it getting cold. So about how much heat does the heat pump remove and would this little light bulb make that much difference?
I estimate that to cool down 1 litre of water from room temp to 4°C would take about an hour. This is based on experience of putting Jelly in the fridge to set and is a very rough estimate but can't be that far out. So the amount of energy lost from the water = 4200 x 26 = 109200J
If this is lost in one hour then the energy lost per second = 30.3 J
That's 30W. And what is the power of the light bulb? Yep, 30W
No wonder the pump is working almost all the time.
I have now solved this by sticking tape over the switch, the problem now is that the light doesn't come on when I open the fridge door. A minor inconvenience. Just have to move that clip on light you can see in the photo over the oven, placed there because the lights in the cooker hood don't work either.
Since writing this blog entry I have looked inside the fridge and seen that the light bulb actually has a power of 15W. The previous value of 30W came from the manual supplied with the fridge. Just goes to show how careful one should be when looking up data. It also explains why the inside wasn't room temperature.
Dad's Techno
Posted on 29 October 2011 at 17:00h
Last night I went to see Jean Michel Jarre in concert. He is a Frenchman (which explains the name) who was very big on the electronic music scene in the 70's. My children call it Dad's techno. He once did a concert projecting images onto the pyramids and although there are no pyramids in Bergen I was expecting a good light show. The first time I saw lasers being used in a concert was at a Genesis concert in the 1976. Technology has come a long way since then so I was expecting huge advances and was a little disappointed that the light cone is still pretty much it. The biggest difference is that the lasers are multicoloured. This is a bit strange since according to HL physics lasers are monochromatic so how does a laser change colour? It seems that it's the same way as pixels on a computer screen change colour, by mixing three different lasers, red, green and blue any colour can be created. The cone is made by rotating an angled mirror in front of the beam.
Feeling isolated
Posted on 25 October 2011 at 16:03h
We were discussing an exam question in class and discussing whether momentum is conserved if a system is acted upon by external but balanced forces. To illustrate the point I tried to think of an example where the forces would be balanced but momentum conserved. The only example I came up with was a box on the floor with a ball bouncing back and forth inside it. Now the box is not moving so the forces are balanced but momentum is not conserved as the ball is going back and forth. As is always the case I realised my mistake on the way home. When the ball hits the wall of the box it exerts a force on it, to prevent the box moving there must be an equal and opposite force on the box, this is friction. When got home made an example in interactive physics where I had two constant forces acting on the box. In this case the momentum is conserved as the box moves back and forth.
This video shows what its like if the forces are constant and balanced.
This one shows how the friction and tension change as the ball hits the sides.
Danish regards
Posted on 15 October 2011 at 14:26h
One of my students, Oliver from Denmark, sent me a link to this youtube video. I was just about to write a reply to him then thought that I might as well put it on my blog. The effect that makes the interesting patterns is caused due to the changing phase of the different pendula. When they are all in phase it means that they have all completed whole numbers of cycles. The longest and therefore slowest one has completed 52 and the one next to it 53, yes I counted them. I don't have so much time to spare but if you move down the line they should all complete one extra swing in the same time (1 minute according to the timer on the video). Other patterns are caused by other phase relationships. It would be interesting to see how these patterns change as the curve made by the pendula changes. I think I might have to make something in interactive physics.
Retro techno
Posted on 1 October 2011 at 16:04h
I was wasting time in Singapore airport, I think it was, cruising round the duty free shop seeing if there were any free samples on offer when I noticed this advertisment. Images of people playing golf were being projected onto a bottle of whisky standing in a glass pyramid. Quite an impressive display so I started wondering how the images were being projected. Must be a laser. Holograms maybe. On closer inspection I realised it was just a piece of angled glass reflected the image from a projector. The bottle was placed in the position of the image so they not appeared t the same place. Just like the old no parallax experiments to locate images in mirrors. I was quite taken aback by how such old technology was still able to catch peoples attention. It didn't make me buy a bottle of whisky though, free samples are a much better way of doing that.
While on the subject of optics I often use crocodile physics for doing ray diagrams in class, like the one below. I have quite an old version of the programme but it does everything I want. One problem however is that all the drawings are white rays on black background. If I want to make one to print out take the image into paint and invert the colours.
Lies are more impressive than the truth
Posted on 29 September 2011 at 11:31h
This morning I was doing about alternative sources of energy with my SL class and was asking them how the thermal energy from a solar panel could be converted into electrical energy. They go the idea that an engine was needed but were wondering if the small temperature increase was enough to power one. I don't have a Stirling engine but have seen that they work off the heat from a hand so suggested that something like that might work. To show that it was possible I searched youtube for an example and found a video of a man in a Stirling engine powered canoe. Great I thought and proceeded to explain how the engine used the temperature difference between the air and the water to power the boat. Very impressive but unfortunately untrue. On reading the text under the video I found out that the engine is powered by propane. Below is a much less impressive demonstration of a Stirling engine that actually is powered by the heat from a hand.
Here is the Neus
Posted on 26 September 2011 at 11:55h
My students have been doing an experiment to measure the time for a ball to roll down an inclined plane and today's lesson was spent discussing uncertainties and how important they are.
Taraah....
That was good timing. One of the biggest physics news stories ever and its all about uncertainties. The measurements have big random errors but by repeating many times they can be averaged out. However if there is a systematic error then no amount of repeating will get rid of it. By reading the headlines one would think that measuring the velocity of a neutrino was just like measuring the velocity of a ball. Make two markers and time how long it takes to go between, the problem is you can't see neutrinos, they are detected somewhere at the start and dissappear somewhere at the end. If you can't be sure where they are how can you be sure how fast they go - you can't. One might also think that the speed of neutrino's had never been measured before. It has and guess what, less than the speed of light. So my money is on Einstein.
Anyway it was, for me at least, a great teaching moment when the point I was trying to make suddenly became reinforced rather strongly.
Some interesting information here at wired science
And for some more details on how thhe velocity is measured Ethan's blog
Interactive students
Posted on 25 September 2011 at 13:17h
Ever since I got a SMART board 5 years ago I have been using Interactive physics to demonstrate just about everything in the mechanics part of the course. Watching red balls fly and blue boxes slide can become a bit dull so I have started spicing it up by attaching students to the objects. I started with just heads but a head swinging on the end of a rope doesn't look very nice so now I have attached bodies. All you have to do is find a photo, copy and paste it in paint - select and copy the bit you want - paste it into IP - draw a similarly shaped object in IP - highlight both objects - select attach picture from the object menu.
Zip wire
Posted on 23 September 2011 at 07:57h
As one of my CAS activities (at UWC's Teachers do them too) I supervise a group of students who instruct groups of young children in rock climbing. When the weather is really bad we can't climb up rocks so we slide down them instead. To be more precise we slide down a rope like the one in the picture but with rather more attention to safety. Yesterday was one such rainy day and one of the instructors was a HL physics student so the conversation naturally turned to physics. Why is the slide so much faster when its wet? When does the kid reach maximum velocity? If the rope snapped would the kid be catapulted into the fjord? With so many questions this seemed like a good topic for a design exercise. All you need is a rope slide with adjustable tension.length and height and an assortment of at least 5 different sized children.
Robin Hood
Posted on 17 September 2011 at 12:34h
Like Robin Hood I was born in Nottingham so have always liked to play with bow and arrows. I used to make them from sticks cut from a hedge and a piece of string, I have often thought that this could be a good basis for a design lab but never got round to it until now. I had no difficulty thinking of 10 research questions in a couple of minutes, hopefully my students will find it as easy. Subscribers can read my 10 here.
Actually tried this one out today and the students (SL) managed to come up with loads of interesting research questions. As you can see in the photo some were more William Tell than Robin Hood but there you go. Managed to quell the idea of mounting an attack on the Environmental Systems classroom which is probably a good thing since they were busy digging soil samples with real spades and forks. They would have simply laughed in the face of our straws and cardboard as they mounted their counter attack.
Big classes
Posted on 14 September 2011 at 08:36h
The start of a new term is often quite busy what with all the new students and everything. Maybe not the best time to develop new resources but sometimes you have no choice. This year I discovered that I have 18 students in each of my first year classes and the practical program has apparatus for 16, rather than buying extra equipment I thought it might good incentive to write some new practicals so I've been spending time in the lab with my EE supervisee Said trying out some ideas and collecting data. The result is 3 new kinematics labs:
The rolling ball utilises video analysis in loggerpro to measure the velocity of a ball after it has rolled down an inclined plane leading to a value for g.
The card drop measures g by timing a rectangular card falling through a photo gate.
Angle of a slope investigates the relationship between the angle of a slope and the acceleration of a cart rolling down it, a nice application of vector components and another quite good value for g.
I am not going to use these practicals for assessment so I have written help pages providing instructions on how to analyse data, draw graphs and evaluate results. Hopefully after doing these 3 my students will know what is required of them. I have also prepared exemplar reports to give some ideas about the sort of complexity required in the evaluation to score top marks.
As luck would have it several students have now dropped physics so I didn't have to do all this work after all :-(
Walking the gangplank
Posted on 8 September 2011 at 12:47h
I always think about physics when I travel on the boat between Rysjedalsvika (bet non nordics can't pronounce that one) and Bergen. This is most likely because am always on the way to or back from a workshop. A couple of months ago I noticed the thing in the photo. It's suspended bridge for getting onto boats, a sort of cantilever. Kant is Norwegian for edge, this seems to fit nicely with what a cantilever is; a lever fixed at one end to an edge. I wondered if this cantilever is actually kantilever in Norwegian but it isn't. The cantilever in the photo (it was raining hence the blobs of water on the window of the boat) is supported by a rope at one end. As one walks along the bridge the tension in the rope will increase. The component of tension that supports the end is Tsinθ so if the rope has to support a weight W the Tension will be W/sinθ. So the tension depends on the angle between the rope and the plank. I wonder if the person who built this calculated the Tension or if they just attached the rope to the most convenient tree. Builders have a very good feeling for this sort of thing, they may not understand how to take components but they know what the angle should be. Reminds me of one of the TOK essay titles on offer this year;
"4. When should we discard explanations that are intuitively appealing?" Not this time it seems.
Yesterday afternoon I walked into the staffroom, sat down with my cup of coffee and joined in a lively discussion on TOK. After about 10 minutes and several failed attempts by me to change the subject from TOK to something else, I realised that I had walked in on a meeting of the TOK teachers. Oops. Quick exit.
Dragline
Posted on 5 September 2011 at 17:40h
The ability to drag a best fit line is a great new feature in Loggerpro. Simply place a manual fit as before, close the dialogue box then double click the Manual fit label. Down at the bottom of the manual curve options you will see "enable line drag" check the box and drag the line whoopee.
Jet jump
Posted on 30 August 2011 at 15:49h
I'm on that boat with internet again travelling home from a long weekend in Singapore suffering from jet lag or jet jump as is should be called on the way out. I was out there leading a category 3 workshop on "enhancing IA ith ICT". It's a new workshop involving a lot of hands on stuff. Quite refreshing not to be bogged down with moderation although it did come up a few times. We covered a lot of ground including using spreadsheets for data analysis and modelling, creating simulations with Algodoo, making screencasts, using loggerpro, video analysis and much more. I learnt how to add slides to excel spreadsheets and found out that loggerpro has a new feature enabling the lines to be dragged into place. Since it was an ICT workshop we used a Wiki to share results. You can see it here.
The photo shows some of the participants working on an exercise where we simulated what it would be like to plan a group 4 project with another school using email and skype, possibly an IB workshop first?
Gunbrella
Posted on 21 August 2011 at 12:41h
I was visiting my mother recently and it was raining so I borrowed an umbrella. Maybe I should add that I was going out so borrowed an umbrella since it wasn't raining inside the house and anyway opening umbrellas inside is unlucky. That's why in the film clip below my brother is opening the umbrella just outside the back door. Anyway the thing is that when I pressed the button to open the umbrella it exploded out of my hand, the spring was far too strong. I actually think it could do some damage and was certain that this wasn't an umbrella at all but some sort of anti mugging device disguised as an umbrella. Once you knew what was going to happen it wasn't quite so shocking but it still has quite a kick. It's all to do with Newton's 3rd law of course, as the umbrella end is forced forwards the handle experiences an equal and opposite force pushing it into your hand.
SMARTboard with visually impaired students
Posted on 20 August 2011 at 13:23h
Sometimes we have students in our classes who struggle to see the writing on the board. I thought it might be an idea to share my desktop with them via skype so that they'd get a copy of the notes on their laptop which they could zoom in on. This solution is not very good. The students can't scroll the notes and also can't click any hyperlinks. Here is a solution that I devised this morning.
- Set your notebook file so that it auto exports on changing page (an option under timesaved in the file menu). Set to export your notes as pdf to a web server such as your schools intranet.
- The student views this file using a web browser such as firefox. In this way the file can be viewed without locking it. That means that you can keep exporting the file while it is being viewed.
- As you work on the board use the next page arrows to quickly export your notes whenever you make a change(you have to go to next page and then back again but it only takes a second).
- The student then refreshes the page to view changes. By downloading an add on firefox can actually be set to refresh automatically.
Having played with this method I have discovered one problem. When the student refreshes the screen they go back to page 1. I haven't found a solution in firefox yet but there is an alternative. Instead of exporting the notes to a web server they can be exported to a shared folder such as a folder on the schools network. The student then uses a PDF reader such as SUMATRA to open the file. This open the file but doesn't lock it so every time you export it refreshes. This solution is also a bit quicker as it doesn't rely on the internet.
I have also discovered that for some students white writing on a black background is easier to see. This isn't a problem with windows 7 where the screen magnifier gives the option to display negative.
The bell worked
Posted on 18 August 2011 at 19:24h
Today was meetings again but this time we had meetings about how we teach. Specifically related to the use of language in our classes. I teach students from a range of backgrounds with different levels of English, some can hardly say a word. For one of the exercises we were asked to take a piece of student work. My partner in the group work took with him a TOK essay. It was written by one of my students so I read it to see if any of my bell ringing had taken effect. I should explain that I ring a bell every time I want the students to realise that I am talking about something that might be useful to discuss in their TOK class. I was pleasantly surprised to find several references to physics in the essay titled; "A model is a simplified representation of some aspect of the world. In what ways may models help or hinder the search for knowledge?" Good to know that this technique works as well with students as it does with dogs. Subscribers can read the essay here.
Never too young
Posted on 16 August 2011 at 19:40h
Today was the start of term at RCNUWC. Can't complain after 10 weeks of holidays. We always start with a week of staff meetings so a nice easy run in. The students arrive this weekend then I'm off to Singapore for 3 days to run a workshop on ICT. I tend to travel more in the term time than holidays.
During coffee break I was watching this little girl, the daughter of a member of staff, playing with her milk bottle in the staff room. We put it on the table cloth then she got it by pulling the cloth towards her. After a while playing this game we realised that maybe its not a good idea to teach small children to pull table cloths. But hey, she's not my daughter. I once taught my neighbours little boy to put stones in shoes. His parents always wondered why they always had stones in their shoes, until I resolved the conundrum some years later recounting the story at a dinner party.
The bottle on the table cloth could be an interesting EE or IA design topic. If you pull the cloth fast enough the bottle will stay where it is. If the bottle is heavy it will have more inertia so the cloth should slip out more easily. Lots of variables to invetigate. Frictional properties of the cloth, mass of the bottle, surface area of the bottles bottom etc. Interesting as this is I decided not to try explaining this to the little girl.
Banknotes
Posted on 14 August 2011 at 13:34h
Last week I was in England visiting relatives so had to travel to the Midlands from Gatwick, I didn't need a car so decided to take the train. I haven't taken a train in Britain for about 30 years so this was going to be a bit of an adventure. Collecting tickets booked on line was a bit of a challenge as was reading the underground maps but for a colour blind country boy I did OK. Apart from the proliferation of fast food establishments at major train stations, the thing that struck me most was the speed of the trains. Euston to Rugby in under an hour seems pretty quick to me. I've mentioned banked tracks many times in physics lessons but this was my first experience of travelling on a train the leans into the corners. I was dying to do some simple experiments with cups of water and pendulum bobs but decided against it. I bet you could do some interesting stuff with an ipad.
The radioactive boyscout
Posted on 5 August 2011 at 13:03h
I've never clicked one of those google news items that appear at the tiop of my email window before but today one caught my eye. "Swedish man's plans for home nuclear reactor spark alert". My initial reaction was that it was complete nonsense but I decided to investigate and discovered the radioactive boy scout who seemed to be on the right lines. I'm still not convinced that he could have amassed enough radioactive material from gas lanterns and smoke detectors but according to Mark Foreman's blog he was on the right track. This video gives the outline. According to Factsheets on biological and chemical warfare agents a smoke detector contains only 0.00000029 grams of Americium so more than 3 million will be needed to produce 1g.
If nothing else, the dubious nature of some of these links provides lots of material for a TOK discussion.
Trout and about
Posted on 1 August 2011 at 09:25h
Although this week has been sunny at last the rest of the summer has been overcast and rainy, good weather for fishing. Where I live there are many possibilities for fishing both in salt and fresh water. My particular passion is fly-fishing but due to an elbow injury have had to limit myself to a lightweight fly rod that I can cast without pain. The rod is very thin so bends quite a lot even with a small fish on the hook. One of the functions of the flexible rod is to prevent the line breaking when the fish tries to get away. When fly fishing for trout the last bit of the line is very thin with a breaking strain of only a couple of kilogrammes, however it can be used to catch fish that are both heavier and capable of exerting more force. When the fish tries to pull away, the rod bends, this makes the time of acceleration greater and hence the force less (F=m(v-u)/t). To get the fish on land it either has to be dragged into shallow water and picked up or netted with a landing net (in my dreams).
There is a lot of interesting physics in fly-fishing; The way the tapered rod bends, the stretch of the line and most interesting, the flight of the line. There are many different types of cast but the one I use the most is called the single haul. In this cast the line is taken in with the free hand just before it is propelled forwards, this gives the line more speed sending it out further. To cast well the weight of the line must be matched to the rod, the weight distribution of the line is also important, line with weight forward seems easier to cast further. Lots of interesting EE topics here, pity I only have 2 candidates this year. maybe I'll have to do another one myself.
Moses drove a tractor
Posted on 26 July 2011 at 11:11h
There has been a lot of rain over the past few days and even though the road drainage in Norway is pretty good there have been some floods. A farmer in a community not far from where I live has a novel way of helping motorists stranded by a flooded road. He drives through the water with the front loader lowered in front of his tractor causing a bow wave. The stranded car then simply drives behind the tractor in the trough created. I would like to see this in action. How close to the tractor must the car be? How fast does the tractor go? What if the car falls to far behind the tractor? Does it only work for short cars? Does it work at all or is this a joke?
Shady business
Posted on 12 July 2011 at 07:41h
The most pleasant way to travel to and from Bergen from Flekke (where I live) is to take the fast boat. This is not only the most comfortable alternative but has the best views and free internet. As I was speeding out of Bergen the other day I was inspired to take a photograph of this breathtaking view. I've only got a mobile phone that I use as a camera so the photo doesn't quite do the scene justice but you get the idea. It reminds me of one of those Heaton Cooper paintings of the lake district that my Father used to like so much. It's the way the more distant mountains are a lighter grey than the closer ones. I have been wondering what causes this effect, I thought it could be due to mist. The light from the most distant mountains travels through more mist so is less intense but wouldn't that make them darker? Maybe it's possible to calculate the distance to the mountains by measuring the greyness of the pixels. You can do this in Paint.net by displaying the colours whilst using the colour picker tool.
I've been thinking about this and have come up with the following attempt at an explanation: The sky in the distance is the brightest part of the picture and since the sun is behind me the light coming from this region of the sky must be scattered light. The most distant mountains reflect light but there will also be scattered light. The closer mountains reflect light but there will be less scattered light since there is less atmosphere between the mountain and camera. So the closer mountains appear darker than the distant ones. I don't know if this is true or not but it seems to be plausible.
Jetset
Posted on 11 July 2011 at 08:06h
I was sitting on the airplane coming back from a workshop in Kazakhstan and got to thinking about the lights. There are a lot of lights in a plane and the must consume a fair amount of electrical energy but where is the generator? In a car the generator is connected to the drive shaft via a rubber belt but what about a jet engine? There is a drive shaft or axle in the centre of the engine but where is the generator? I didn't think it would be possible for the generator to be connected directly to the axle since it then it would be in the middle of the engine and a "fan belt" seemed out of the question since it would have pass through the flow of gas. I couldn't think of the answer so when I got home I looked it up and and found the answer that there is a bevel gear connected to the axle that turns a rod connected to a generator outside the engine, probably in that lump connecting the engine to the wing. Some planes also have a wind turbine underneath the fuselage if the jet engines fail. When standing at the airport the generators don't work and batteries are heavy so the plane has to be plugged in to the mains.
Glass balls
Posted on 3 July 2011 at 12:08h
I was in Bergen the other day with some time to spare so was wandering aimlessly and caught sight of the girl in the picture. I'm not a big city person so maybe this is old hat, but I haven't seen this as a street performance before although I have seen it on the tele once. The normal offerings in Bergen are a couple of silver "statues", a Bolivian pipe band and a whole load of musicians from various parts of the world. The idea of the glass ball is the illusion that it is floating in the air, the performer moves their hands around it and it stays still. The ball has quite a large mass and hence large inertia this combined with a low friction surface means that if the hands is moved under it it stays in one place. I'm not sure what this all has to do with love, peace and psychedelic music but she seemed to be doing good trade.
The guy in the video is considerably better than the Bergen girl but could do with a bit of music.
wireless electricity at Riga airport
Posted on 2 July 2011 at 11:30h
The point is that although there are many options for free wireless internet there aren't any for wireless power which is why am having to sit on the floor by the plug socket as I while away 10 hours waiting for my flight to Kiev. Hopefully the battery will be charged soon as the floor is very hard. Maybe I should have borrowed the solar charger that my son bought recently to charge his mobile phone whilst attending the music festival at Roskilde. He was very pleased with the purchase saying how it would save him lots of money. At £35 he will have to charge his mobile up quite a lot of times before he turns a profit. Anyway as he pointed out when I told him, at least he is saving the planet.Pity it wasn't waterproof
Schedules
Posted on 27 June 2011 at 18:13h
Its raining again so I'm spending more time inside than I would like to be. Actually today I spent most of the time outside washing the walls of our house. I don't remember ever washing the walls of a house in Britain but in Norway we have wooden houses and its important to wash away the algae that accumulates on the paintwork. Anyway I apart from today I have been spending a lot of time indoors so I have decided to prepare a set of problems for my students to do. These are like paper 2 problems but without the steps. Last year I realised that some of my students simply didn't know how to go about solving problems so to rectify this I am writing two problems for each lesson. The idea is that students will try the problems after the lesson, each lesson I will have a quick look at all my students attempts then release some hints and solutions on the website.
My students weekly schedule will now look something like this
Lesson 1
Measurement
Homework
Review measurement
Try measurement problems
Lesson 2
Show attempt at problem
Short test on measurement
Vectors and scalars
Homework
Check solution to measurement problems
Review Vectors and scalars
Try vector problems
Lesson 3
Show attempt at problems 2
Practical 1
Homework
Write up practical 1 (hand in next practical class lesson 6)
Check solution to vectors problems
And so on............
Maybe this stricter routine will encourage my students to organise their work schedule. I don't really like having to check up on my students to make sure that they have tried the problems but I think maybe it is necessary.
Sand castles
Posted on 21 June 2011 at 08:08h
Last weekend I went surfing with my son to a beach called Hodevik on the west coast of Norway. The waves weren't so big so we spent quite a bit of time sat on the beach waiting for the tide to change in the hope that when the water went out the waves would pick up, they didn't but as we sat on the beach we noticed something interesting in a little stream running across the sand. The sand on the stream bed had been formed into ripples and as we watched we could see the sand grains being moved across the bottom. At other places holes had been carved in the sand and grains were being sucked out. The process of ripple building is initiated when the speed of the water is enough to pick up grains from the bottom, these are taken downstream and dumped, as they are dumped more sand is disturbed and the process goes on. One thing that didn't seem to make sense was that since the peaks stick up they would be most likely to be knocked down so how come they remain. I found the answer in Wikipedia, the peaks are continually being blown down as the sand is shifted downstream, the ripples are not static. The wavelength is related to the water speed, faster water will carry the sand further resulting in a longer wavelength. I also found some evidence that the water can become turbulent as it runs over the peak, this causes sand to be picked up on the downstream side of the peak, This is what I was observing in the hole.
The origin and growth of Ripple-marks
Breaking the rules
Posted on 14 June 2011 at 11:29h
Thanks to John McMurtry for passing on this clip about the physics in animations. Looks like we are all teaching these budding animators the wrong thing, so what sort of physics are they learning. I think its funny when Damon Riesberg says to one of the animators "that just wouldn't work in the real world", well most of the film wouldn't. Another out of context quote is Alejandra Garcia "physics has become another science". It's great stuff and I guess what they are saying is that they are using the same sort of models used to model the real world to model their imaginary one. So within their world you have to obey the rules but they aren't the same as the rules we use. That course on "animation physics" sounds interesting but is it physics?
Need 4 speed
Posted on 10 June 2011 at 15:29h
I've seen a lot of these wing suit clips on youtube but this one just blew me away. First they fly under some electricity wires then between a cliff and a tree but the gorge has to take the biscuit. It seems total madness but i guess they have more control than it appears. I looked up some facts on wikipedia and found out that the vertical component of their velocity can be as little as 40km/hr, that's not that fast compared to the terminal velocity for a free-fall parachutist which is more like 200km/hr. however they move 2.5m forward for every 1m down so the forward velocity is around 100km/hr. This means they can fly parallel to the ground on a 25° slope. The routes are mapped on GPS and so they can compare flights and get closer to objects like trees and rocks. Now I think its time to put my head back in the fridge.
A fridge too far
Posted on 7 June 2011 at 15:58h
Today I went to a funeral at the local church and forgot my reading glasses which meant I couldn't read the words to any of the hymns. This is particularly problematic living in Norway since all the hymns are in Norwegian so even though some of the tunes are familiar the words are not. Anyway I struggled on by trying to latch onto the words of the person sat next to me. At the end of the service the congregation went outside to the graveside where another hymn was sung. Interestingly I found that my eyesight was much better standing outside than sitting in (although my singing wasn't really that much different) so why was that? I thought maybe it was due to the colder temperature. Could the lens be contracting or the refractive index of the fluid changing? When I got home I did a quick experiment. I tried to read with my head in the freezer. The result? A total failure, it made not a blind bit of difference. Pity, I could have made millions replacing glasses with ice packs. No need for expensive surgery just walk around with your head in the fridge. One of those wine coolers with a glass front would have been perfect.
Ghost stories
Posted on 2 June 2011 at 17:07h
I was on my way out to the rope slide with a group of students and some children from our campschool (It's a major part of our CAS program) when another student called my name and came running over.
"Do you believe in ghosts" he said. That's an easy one "no" I replied. "Why not". "Well they don't obey the laws of physics, they can go through walls and stuff. Well if they do exist then they aren't part of our physical world which they're not suppose to be anyway are they. Maybe spiritual isn't physical". Talk fast and maybe he'll go away. "What do you mean not physical". Blast he's still here. "I mean they don't fit in with our physical models, that matter should interact in certain ways." "But what if the laws are wrong" hmm, here we go and he went on. "You see we were having a discussion in the chemistry class and the physics students were disagreeing with the chemists. The physics students said that nothing could travel faster than the speed of light because it was against the laws of physics, but what if the laws are wrong?" "The theory that says that bodies with mass can not travel at the speed of light is based on certain postulates which have strong experimental support, what is your theory that particles with mass can travel at the speed of light based on?" Then he left.
Hot Wheels
Posted on 1 June 2011 at 12:34h
I used to have hotwheels when was a child, little cars that rolled down a plastic track. You could arrange the track so that they'd do jumps and loop the loops etc. I've always thought that it would be great to have a class set of cars and track. Could do some cool experiments. More visually appealing than a pasco track and cart at least. Maybe one day.
The photo is not a toy car but a real one. Take a look at the video of it doing a world record jump. The strange thing is just how flat the jump is, hardly parabolic, well if it is then it's the very top of the curve. The car seems to be flying rather than jumping. The car doesn't really look like a wing profile (maybe slightly) so it's all to do with the angle of attack I guess. Notice how the car revs up in the middle of the jump, is this to keep the front of the car raised? If it is then it's a nice example of conservation of Inertia, pity that's not on the syllabus any more.
Scoris or scorisn't
Posted on 28 May 2011 at 16:43h
Not much time for blogging or writing new worksheets for the website since I am bogged down with e marking and the thought of spending more time at the computer is not so appealing (so I'll make this quick). The system we are using is called scoris and it seems pretty good. You basically download 20 papers at a time and then are able to mark them by candidate or question by using a selection of stamps. Before starting to mark you have to be able to be close enough to the chief examiner and that's not easy, of course everyone makes mistakes and that includes the chief himself so matching scores can be problematic. Every 10 scripts you get 2 already marked ones (seeds) if you don't match the chief examiner you get suspended. To be honest the whole process is quite stressful, much more so than the old method. the marking on the computer is fine but the big brother aspect isn't. Having said that system is pretty good I have to remark on one thing that is starting to get on my nerves. Since section B (I mark paper 2) has a choice of questions student leave 2 of them blank but the marker has to open every section of every question and acknowledge with an NR (No response). Why don't they programme the computer to do this. f a computer can read a car number plate it can surely tell if one of those boxes is blank. Also some of the questions just have a single number answer like 0 or 2V. I'm the computer could handle these too.
By the way, that screen shot is an actual exam question answer. I wonder if it's ok to reproduce copyright material as long as the resolution is low enough?
The icelandic tug
Posted on 23 May 2011 at 13:38h
Have you seen that Top Gear episode where they drive to the North Pole in a Toyota Hilux? I've watched it several times and am intrigued by the way that the truck is pulled out of a crevasse by the Icelandic snow driving experts. There isn't enough friction for one truck to pull the other so they attach an elastic rope between the trucks with a lot of slack in it. The pulling truck then drives off as quickly as possible. When the truck is travelling at quite a speed the rope becomes tight and pulls the other truck out of the hole. So there isn't enough friction for one truck to pull the other but there is enough for one truck to accelerate on it's own. When the rope comes tight the force exerted is pretty high. You may have used the same principle to break a piece of string by holding it slack between your hands then snapping them open. The force exerted would be even higher with a non elastic rope but would almost certainly snap it, the elastic rope not only reduces the force but gives time for the second truck to start moving without stopping the front one. I have often thought of recreating this in interactive physics and today I got round to doing it. I would have posted a link to the actual video but I couldn't find this bit in any of the clips, obviously no one else thought this bit was interesting, that or I dreamt the whole thing up.
Genius of Britain
Posted on 19 May 2011 at 08:58h
Last week a fascinating programme from Britain's Channel 4 was aired on the satellite channel BBC knowledge. British viewers probably saw this ages ago so it's old news but it was new for me. The programme was a potted history of the role played by British scientists in the development of science since its beginning in 1964 (!?). I found the series very interesting and learnt lots of interesting little facts to take to my class, unfortunately I have forgotten most of them but do remember that at the age of 3 Maxwell (or was it Faraday) was told that a stone was blue and replied "but how do we know it's blue". As a matter of interest I thought I'd see how the series would rate alongside some of the IB Aims for Gp4 subjects.
1. Provide opportunities for scientific study and creativity within a global context that will stimulate and challenge students.
The programme did show how the achievements of British scientists affected global development but was completely biased towards Britain so wouldn't do very well as far as internationalism goes.
5. Engender an awareness of the need for, and the value of, effective collaboration and communication during scientific activities.
Yes and no. The point that each generation's achievements were based on the previous generations work was strongly emphasised but the fact that there were some non Brit involved was generally left out. The only non Brit I can remember was Dr. Hans von Ohain who beat Sir Frank Whittle to get the first Jet plane in to the air. Hmm, I'm sure we weren't told that at school.
8. Raise awareness of the moral, ethical, social, economic and environmental implications of using science and technology.
Yep, most of the science was put into context, industrial revolution, wars etc.
9. Develop an appreciation of the possibilities and limitations associated with science and scientists.
Not really, this was about the successes not failures.
10. Encourage an understanding of the relationships between scientific disciplines and the overarching nature of the scientific method.
Very much so, the programme was about science not just physics.
Sunshine of my lies
Posted on 18 May 2011 at 13:23h
I was just heading out yesterday evening when I was faced with the scene shown in the photo. The sun was low and shining straight through the glass of our front door. You can clearly see the path of the light reflected by dust particles. So what's so interesting about that? The sun is always drawn as a yellow ball with rays radiating from it, nothing wrong with that until you come to consider rays on the earth and tell students that they are parallel. They don't look parallel even in my photo it looks like the rays are spreading out a bit but that's due to the perspective not the angle of the rays. This is the sort of problem we are always coming up against as physics teachers. How can you get them to believe something when they have seen with their own eyes that it's not true?
On a similar theme have a look at this.
The bang and the boing
Posted on 17 May 2011 at 14:54h
I was bored doing an exam supervision for Spanish A so kept myself awake by trying to think up some new practicals for next year. I don't have many examples of conservation of energy so thought that might be a good area to think about. The idea I came up with was to project an object vertically upwards from a compressed spring, I thought of using a tube with a spring at the bottom and a pencil as the projectile. After the supervision I went to the lab to play around and couldn't find a suitable tube in any of the drawers in the chemistry lab so decided on inverting the idea putting a rod inside the spring. Behind the door in my lab is the top section of a carbon fly rod that was broken when I tried to teach one of our formers maths teachers how to fly fish, once the eyelets were removed this served as a perfect rod so I mounted it in a clamp stand and started experimenting firing a cotton reel up it. After a while I realised that it was very difficult release the cotton reel so that the height was the same for a given compression. However when I let the reel drop onto the spring I could tell by listening if the spring was fully compressed or not, bang or boing. So by increasing the drop height I could measure the minimum height required to fully compress the spring (the point when the boing becomes a bang).
When this occurs mgh = ½kx2
Now if the same spring is used ½kx2 is a constant so m ∝ 1/h
I changed the mass of the reel by winding some solder round it then took a quick set of measurements resulting in the following graph. I was quite pleased about, especially the intercept. Will check out if the value for k that I get from the gradient is reasonable or not.
Subscribers can find worksheet and teachers notes here
On the fringe of Eurovision 2011
Posted on 15 May 2011 at 08:22h
Congratulations to Azerbaijan for winning the Eurovision song contest. I didn't watch the whole thing but did see the start and was very impressed with the stage that had been set up in Düsseldorf. The whole back of stage seemed to be one giant TV screen. The way the Earth appeared during the Finish entry was particularly impressive. This morning I was curious enough to find out who had won and what the song was like so I looked it up on the Eurovision website. I can't say that I like the song because I don't like it however the lighting did catch my eye particularly the effect in the photo. I can't be sure but I don't think these fringes would have been visible to the live audience, think it is a Moiré fringe due to interference between the pixels on the screen and the pixels in the camera, as the camera panned out the fringes shifted. You can see it here after 58s (turn the sound down if you don't like the music). I would like to see Pink Floyd or Jean Michel Jare with a light show like that.
Ever since writing this blog entry I have been thinking of how this effect is produced. First I tried taking a photo of my blank computer screen to see if I could get fringes. The first picture worked beautifully but after that the fringes just disappeared. I have no explanation for that but here is the photo when it worked. As mentioned previously I think this is caused by the fact that both the object and image are made of pixels, when they line up you get a bright spot when they don't it's dark. Next i started playing around with dots. I drew a load of them in paint then superimposed them. You can clearly see the effect when the spacing of the dots are not the same in the screencast below. I guess this is a sort of negative version since when the spots coincide it gives a small spot but when they overlap you get a more prominent big dot. if you want to play with my dots you can download them here. Open in "paint" select one of the grids and slide over the other (make sure the selection is transparent).
Well I just had to try reversing the colours to see if I could get the true effect rather than a negative and it worked a treat. I can see this is a nice analogue of beats. If so the spacing of the fringes should be a function of the difference in the spacing of the two sets of dots.
Here is what you get if you change the spacing. I tried using the beats equation to find the fringe spacing and got an OK result but not as close as I would have liked. I can see a nice practical coming out of this.
Nice paper 1
Posted on 13 May 2011 at 12:24h
I've just finished doing paper 1 and paper 2 (time zone 2) on my tablet pc so I'll upload them for subscribers later today (Takes a bit of time cropping all the images).
A couple of my students thought the papers were difficult but I always say if the knew it was difficult then that's a good sign, at least they understood the question.
A couple of questions on paper 1 were a bit strange. didn't like the first one about the uncertainty in speed.
A body accelerates from rest with a uniform acceleration a for time t. The uncertainty in a is x% and the uncertainty in t is y%. The uncertainty in speed is
One would normally calculate the acceleration from the change of speed rather than the other way round so I thought the question meant that the uncertainty in a had been calculated from the uncertainty in speed and time. Anyway the answer you get from that assumption wasn't on offer. maybe I should follow my own advice. "If the going gets tough you've done something wrong".
Another one I wasn't keen on was one about Uranium changing to Plutonium. This takes place by neutron capture followed by beta decay. The answer was neutron capture. I guess most students will have looked at the increase in A and gone for that anyway.
Finally there was a question about tidal power asking how the PE is related to depth. The quick answer is proportional since PE = mgh but on further consideration the mass of water is also proportional to h so PE ∝ h2 .
Anyway, it's not easy making up original mc questions so all in all a good effort.
Paper 1 May 2011 Tz2 solutions (for subscribers:-)
Paper 2 May 2011 Tz2 solutions (Unchecked and also for subscribers only)
Leaky pipes
Posted on 10 May 2011 at 19:03h
During the winter the roads in Norway are covered in ice, to make them less slippy the council puts grit on top of it. During the course of a winter as long as the one we have just had, there is a lot of grit spread on the road, so when spring comes (now) it has to be swept up. This is done by connecting fire hoses to the hydrant and using the high pressure water to squirt the grit into piles. The maintenance dept. at the college were doing this the other day and to extend their hoses they had bought some old hoses from the fire service. I have never seen hoses with so many holes in before. As you can see in the photo water was spraying out along their whole length. So I was wondering how the length of the little jets vary along the length of the pipe. I would've thought that they would decrease as you move away from the hydrant. Each hole causes a reduction in pressure that results in the next jet being smaller. But what about those long sprinklers that the wheel across fields in the summer? They seem to have fairly even jets.
Colourblind
Posted on 9 May 2011 at 09:50h
Can you see the red flowers in the middle of this photo of our garden? Well I can't. I think it's because I am colour blind but it might be because there aren't any, only you can tell (assuming you are not colour blind too). When the first edition of the SL book came out we had the reverse problem. There was a photo of a colour blindness test that had been picked by someone who wasn't colour blind and I could see the number that I wasn't supposed to see quite clearly.
Super size me
Posted on 8 May 2011 at 19:33h
This weekend is confirmation weekend in Norway which means hoist the flag and eat lots of cake. The daughter of one of our neighbours was getting confirmed so Hilary decided to bake a cake. The recipe was for a normal sized cake but confirmation Sunday calls for a super size cake so Hilary went for double quantities. The cake was a carrot cake by the way. You'd think that double quantities would mean double baking time but after double the half hour for a normal sized cake the cake was far from ready, now carrot cake is supposed to be moist but this was dripping wet. After an hour and a half it was finally cooked as you can see in the photo.
I was wondering how you calculate the effect of increasing quantities. Here is a rule of thumb I got from a google search:
- Remove 1/3 of the cooking time.
- Double the remaining amount.
-
Add your original third back on.
Why not multiply by 5/3?
That would give 50 minutes which wasn't nearly enough.
It's probably got something to do with the shape of the cake as well.
Doubling the ingredients doesn't double the distance to the centre so why does it take so long to cook? maybe its something to do with the carrots?
Exam invigilation boredom
Posted on 4 May 2011 at 07:29h
Yesterday I did my first exam invigilation of the season. This is probably the most boring aspect of being a teacher. I guess it's not bad being paid for doing absolutely nothing but that doesn't make it any easier. The shoes in the photo were left outside the exam room, maybe one of the students thought that removing their shoes would make them think better. Shoes are a good thing to focus on. I don't want to disturb the students so I find that looking at their feet whilst walking around has the effect of making me invisible. Whilst looking at shoes I have noticed an interesting trend. Two years ago the majority of student wore converse baseball boots now there was only one pair out of about 60 students. Converse are obviously out. Good job too, they really aren't very practical in wet Norway. If I sit at the back no one can see me so I don't have to focus on shoes any more it is then that I noticed two interesting facts. Firstly all the girls except one had tied their hair up. Had they arranged this is was it purely coincidental? If I had been the loose hair girl think I would have borrowed one of the elastic bands used to bind the papers together. Secondly two Latin American students were wearing hoodies with the hood up. Looking forward to my next invigilation to collect more data.
Time for T
Posted on 2 May 2011 at 10:38h
A week or two ago my first year students did a design experiment with two strips of meccano. One of them decided to build a T pendulum and investigate the relationship between the time period and the distance between the pivot and the cross piece. I thought the result would be like the pendulum, as the cross piece moves up the pendulum is in effect getting shorter so time period should decrease however it's not that simple. The results show that as the strip is moved up the time period gets shorter up to a certain point when it starts to get longer again. If you think about the pendulum is made up of the vertical strip with its mass acting at the centre and the cross piece which just acts as a movable mass. As the mass is moved up the pendulum length gets shorter but when the mass is attached to the pivot then it will have no effect so the length will be effectively longer this means that there must be some turning point where the time period stops getting shorter and starts to get longer again.
Hmm, confusing.
Beer and crisps
Posted on 2 May 2011 at 10:27h
I like to invent some new practicals every year but when one works so well its worth doing again, the exponential decay of beer is a winner. There aren't so many experiments you can do with radioactive decay so when you find a good one its worth hanging on to it. I actually still have a set of sources and a protactinium generator but its difficult to do a class practical with such limited resources (probably not allowed either). The bubbles work quite nicely because there are a lot of them and they pop quite randomly. I was planning to make an experiment with some of those plastic hemispheres that you invert on the table and they suddenly pop up but they just weren't random enough so I abandoned the idea. The beer one is fun because it's beer (actually non alcoholic beer). Whenever I buy beer I always have to buy crisps (potato chips to non Brits) these have nothing to do with the experiment but add to the party atmosphere at 8 o'clock in the morning. The results are pretty good especially if you use a video camera giving a half life of around 50s and a much better understanding of exponential decay.
Nearly Summer
Posted on 27 April 2011 at 10:39h
The sun is shining and I don't have second year classes any more so thoughts turn to the summer holidays which hopefully means climbing and surfing. No surfing in the fjord so I go to magic seaweed to check out some videos and found this one about surfing a tidal bore in Indonesia. A tidal bore happens when there is resonance between the force of gravity from the moon pushing up the tide and the velocity of a wave in a body of water. There is a famous one in Britain called the Severn bore which is particularly big on a spring tide. The one in the video is rather more impressive than this one and even forms a barrel.
The photograph shows an interesting phenomenon. There seems to be two waves, one travelling down and the other diagonally, watch the video and you'll see what I mean. Also in the video you get a nice shot of the wave refracting as it passes over a sandbank and starts to slow down. The water doesn't look very clean though, chocolate barrels don't sound very inviting.
A close shave
Posted on 24 April 2011 at 15:06h
Yesterday I was having my weekly shave when the shaving foam got me thinking. Why is it blue when it comes out of the can but white when up put it on my chin? The blue colour must be caused because the gel absorbs all the colours in the light except blue which it reflects. When the gel turns into bubbles the surface of each bubbles reflects all of the colours so the foam looks white. so the surface reflects all colours but if reflected from the body of the substance it only reflects blue. The same effect explains why crushed brown sugar looks white. So why are some powders coloured? Is it because some substances are coloured due to surface reflections and others due to reflections in the body of the material?
Maybe Geoff knows?
Dogs don't like digital marking
Posted on 22 April 2011 at 08:45h
If you've ever wondered where those samples for moderation end up well they could be here, piled up on the floor of my study. These are only this years offerings, last years are in my cellar. Only a sample of the sample gets sent on to the senior moderator so that the moderators are moderated, the rest stays here in case I have to do an IMR report. Once the deadline for that has passed the sample material can be destroyed. I've just discovered that there is a company close by that will sort and shred documents for a about 3kroner a kilo so next week I'm taking last years pile down there. It would save a lot of paper and postage if this was all done electronically. Most of the sample is written on a computer anyway so why not simply deliver them online. It's even easier to organise than scanning exam scripts. I mark my students work with a tablet computer so the only time it gets printed is when I have to send the sample. I guess the post office and DHL wouldn't like it and nor would the dogs.
Hard Brain / Soft Brain
Posted on 18 April 2011 at 15:31h
My first year student were doing a design practical the other day and some of them needed to use the datalogger to record their measurements. I find this is a time when having a good selection of sensors and data loggers really pays off. That's why I make sure that all the students know how to use them and what sort of sensors we have. Anyway over the years I have found that students are very quick at finding their way around new bits of software and once they have used data studio and loggerpro once or twice become quite proficient at using all of the features and even find ways of doing things that I didn't know about. But the thing that I don't understand is why, if they are so good at remembering these details, can't they remember that the cables used to connect the charger to the mains hang on the back of the cupboard door at the front of the class, the dataloggers are in the cupboard on the other side and the USB connectors are in the drawer below the dalaloggers.
The land divers of Vanuatu
Posted on 14 April 2011 at 12:06h
It's getting towards that last lesson ever for my second year classes, I've still not finished the syllabus with the HL so no problem thinking what to do there however I finished ages ago with the SL so am struggling to fill the time. Students always want to do something fun for the last lesson but to me its always fun so what's the difference (my students don't accept that feeble attempt to get out of making cakes either). Making physics fun is a bit subjective, to me it means rock climbing, fast cars and surfing but if the students don't share my interests then it might not be fun for them. Anyway, that's their problem, today we did some more rock climbing physics.
When I was instructing a group of students yesterday one of them kept shouting to the person holding his rope that she wasn't holding it properly because every time he fell off he went down. What he hadn't realised was that the ropes are elastic. Falling off whilst lead climbing is a bit like bungee jumping, you fall freely until the rope comes tight, if the ropes weren't elastic you'd break your back. This reminded me of an episode of a TV programme called "Blue Peter" that I saw when I was young. It was about the land divers from Vanuatu, It's bungee jumping from a wooden tower with vines tied to your ankles. I guess its all in the bending of the legs.
Anchors away
Posted on 10 April 2011 at 19:43h
A week ago the weather was at last good enough to start the Friday rock climbing activity so I took a group of students to the cliff situated a 5 minute walk from the college campus. When we got there I was shocked to see that a large part of it had fallen down. Not the bit we climb on but rather too close for comfort. What happens is; water that runs through cracks in the rock freezes in the winter, as it turns to water it expands and pushes the rock apart. When the ices thaws in the spring the rocks fall down. As a result we can no longer climb on the cliff so I must find a new one for the climbing activity. Luckily there is rock everywhere in Norway and this weekend have been developing a cliff only a couple of minutes from my house (closer than the old one). Most of the preparation involves scrubbing the rock with a wire brush, removing grass and trees and placing bolts. The photo shows a bolt anchor. The bolts shouldn't be placed too far apart or the force exerted on each of them will be substantially more than the weight of the person hanging on the rope. Actually the force is twice the weight of the person hanging on the rope since there are two people one hanging and the other holding the rope. That's of course assuming they are hanging on the rope which on this cliff they won't be since its not vertical. Some interesting physics here, maybe I should take my class rock climbing?
Onkalo
Posted on 10 April 2011 at 09:20h
On Thursday I happened to turn on the TV and was "greeted" by a couple of Finnish men staring at the camera occasionally saying something about nuclear waste. Intrigued I sat down to see what it was all about. The editing of the documentary was very special, many interesting camera angles and strange seemingly out of context shots of moose hiding behind trees. The interviews were done in a way that enhanced the finnishness of the scientists. Although I missed the start, the thread that held the documentary together was a message written to people 100,000 years into the future warning them not to enter the nuclear waste storage facility that was being built at Onkalo in Finland. It's an amazing project to store nuclear waste 400m underground in tunnels that will be secure for 100,000 years. As one of the scientists pointed out, above ground is to unstable. People have to be employed to maintain the buildings, wars can happen, governments will change. 100,000 years is a very long time. Underground things are different. The rock at Onkalo has been exactly the same for millions of years, in geological time 100,000 years is not very long.
I had a dream
Posted on 5 April 2011 at 19:23h
I have always thought that the easy way to tell if you are dreaming or not is to see if the laws of physics apply, if they don't then you are dreaming. Last night I had a dream when the laws of physics did apply, in fact I was dreaming of a new practical for my students. Yes its true I dream of physics. The idea that came out of the dream was to project elastic bands across the table at different angles then plot a graph of angle against range. I thought it could be a good way of practising curve drawing and enhancing understanding of projectiles. I didn't actually remember thinking that in the dream but I guess that's why I was doing it. Anyway I tried the experiment this evening flicking elastic bands across the kitchen table whilst my wife was out at a meeting (that piece of information is irrelevant). Maybe I should explain how launched the bands. I drew a line on a pencil and held the band next to the line with my thumb, I then stretched the band over the end of the pencil as shown. I found that as long as I was very careful to position the band in the same place then the results were quite consistent. If there was a twist in the band or it wasn't in the middle of the end of the pencil then it would shoot much further. I actually have two pasco launchers in the lab and have done this experiment by firing balls onto carbon paper. That gives much more consistent results but this way requires more finesse. I didn't spend very long repeating the measurements but got Ok results.
The non zero intercept is interesting, at 0° there is a range of about 8cm which is not far off the amount of pencil protruding over the table.
Completely Bongo
Posted on 3 April 2011 at 17:12h
Last week my first year classes were doing a design experiment with a rubber bung on an elastic band. It's quite a good example and students don't find it too difficult to come up with interesting and do-able research questions. A lot of the experiments revolve around oscillations, often related to the length of time for the oscillations to die out rather than the frequency of the oscillation.
Why is that?
We hardly mention damping but everyone wants to do research questions related to it. Maybe it's a misunderstanding of what time period is?
One of the students was measuring the time period for the oscillation of the bung on one elastic. This oscillated pretty fast so went over to see how he was timing it. Actually, to be honest went over to point out that it wasn't possible to count so fast. To my surprise he was able to count so fast by counting every 4 oscillations. The student in question (It's Oliver) is a pretty good musician and was able to recognise when there had been 4 oscillations without actually counting them. Quite a neat trick. I bet Richard Feynman could do that too.
The 3D puppy
Posted on 31 March 2011 at 17:44h
After doing about the diffraction grating with my HL class I decided to give them a treat and explain how a hologram is made then show them the puppy hologram I keep hidden under the sink (sounds dubious). I know it’s no longer on the syllabus but I do it anyway because the way it works is so neat. My final year project at university was doing holographic interferometry on loudspeaker cones, first had to make a hologram. The first 20 didn't work at all because the box of photo plates had been exposed.
I found this really good explanation in an old journal some years ago when holography was still on the syllabus, the way the photo of the fringes recreates the original wave front is almost magical. To record all the information that is contained in a wave front we need to record the intensity, wavelength and phase. A photograph only records intensity and phase which is why unlike the original scene; it looks the same if viewed from different angles. To record the relative phase of different parts of the wave front we can interfere it with a reference wave.
Consider the blue wave front below.
The relative phase of the wave front can be recorded by superposing it with the red reference beam. The two beams coincide on a photo plate which darkens where the waves add to give a series of dark bands. If the photo plate is the used as a diffraction grating for the red wave it diffracts the light in exactly the same direction as the original blue beam. The blue beam has been reconstructed.
If the blue plane wave front is now replaced with a circular one the diffraction grating produced has uneven lines. If this is now used to diffract the reference beam a circular wave front is recreated. As shown below in my second diagram which shows scant regard for the consistent use of colours.
If it works for one point it will work for the millions of points that make up any 3D object. And by the way, the beams aren't really blue and red they are both the same colour since the waves won't interfere to give fringes unless they are COHERENT. (a class joke)
I’m just waiting for the first holographic computer screens and TV’s. I guess watching 3D TV will take a bit of getting used to; maybe we’ll have to have special empty rooms to view them in as it might be quite strange watching all the action with your furniture in the background.
The balance of power
Posted on 30 March 2011 at 15:30h
Today my first year classes did the magnetic flux density practical that I devised a couple of weeks ago. When I did it I got a pretty good result but didn't use exactly the same equipment as I gave to my students. The balance I used cost about £1000 the one they used cost £5. I think it makes a difference although the accuracy is supposed to be the same, the cheap version sometimes didn't register a difference. I remember reading in the manual (that I threw away) that the balance made a measurement every second or something, or was it 5s? The other problem was with the batteries, they don't last long when connected to 30cm of Nichrome. When I did it I only held the contacts on the wire for a second or two but when no force was registered some of the students held the contact in place a good deal longer. Another problem was those blasted magnets, they are so strong that its really hard to get them apart to place then across the metal yokes.
Oh well, back to the drawing board. I think I am going to modify the procedure by making some coils that fit over the magnets to increase the force. I could also then attach an extra length to act as the rheostat. An altogether neater solution. Better not make it too good though or my students won't be able to think of any improvements.
Inconveniently complicated truth
Posted on 28 March 2011 at 18:20h
It’s atomic physics with the first years and we are working our way through the models of the atom in chronological order. When we got to Thomson and the discovery of the electron I made a statement something like this: “The electrons couldn’t have been atoms because their mass was far too small so were considered to be like small plums in a pudding”. This provoked the obvious question “How did they know the mass of an atom”. Hmm, not quite sure about that. I know how they do it now (mass spectrometer and all that) but how did they do it then?
In 1811 Avogadro came up with the idea that equal volumes of gas at the same pressure and temperature should contain the same number of atoms. If this is the case then it is possible to measure the relative masses of different gases by simply measuring the mass of equal volumes, so 1litre of Helium has a mass 4x the mass of 1 litre of Hydrogen etc. But to know the mass of 1 atom you have to know how many atoms there are and Avagadro didn’t know that even though the number is named after him.
Around 1865, by considering how far gas atoms move between collisions and the pressure they exert on their container, Johann Loschmidt calculated how many atoms there are in 1 cm3 this enabled him to estimate the mass of a gas atom. The derivation looks a bit tricky which is probably why we tend to leave this bit of history out of the story.
Thomson discovered the electron in 1897 so would have known the approximate mass of the atom.
I was going to post a photo of Loschmidt but when I saw what Avogadro looked like I just had to post his photo instead.
How LEDs work
Posted on 27 March 2011 at 19:19h
We were doing about light sources the other day as part of the HL EM option and one of the students asked how an LED worked and why they are so efficient, first some background about semiconductors. Semiconductors are solids so their electrons exist in energy bands rather than levels. The highest band is fairly empty so there are few free electrons to enable conduction, semi conductors are therefore poor conductors, however adding an impurity (doping) can increase their conductivity either by adding free electrons (N type) or an impurity with missing electrons (P type). It sounds like a material with missing electrons shouldn’t increase the conductivity but it does since it allows other electrons to move into the holes. If a piece of semiconductor is doped with N at one end and P at the other a junction is formed between the two halves, this is called a diode. When current flows through the diode, electrons conducting though the N type combine with holes in the P. When this happens the electrons move from high to low energy level resulting in the emission of light.
So why should they be so efficient? If we compare to an incandescent light bulb then to produce light the electrons first have to be excited into the higher energy level, this happens when the lattice atoms gain energy from the conduction electrons. In a diode the electrons are already in a higher energy level so don’t need to be excited there by the material getting hot. Well that’s my theory and I’m sticking to it.
Dirt is magnetic
Posted on 25 March 2011 at 14:09h
The conversation went like this:
Maria: "Is dirt magnetic".
Me: "Well only if it's iron dirt".
Maria: "No I mean stones and stuff".
Me: "If the stones are magnetite I suppose"
Maria: "What does that mean?"
Me: "It means they are magnetic".
Maria: "What about ordinary dirt like on the floor of the Norwegian classroom"
Me: "I don't think so"
Maria: "Well it stuck to my computer"
Me: " So is your computer magnetic?"
Maria: "Yes"
Me: "Oh"
So Maria borrowed a magnet and went to the Norwegian classroom and brought back stones sticking to a magnet. On closer observation the stones looked just like the photo of magnetite we found on the web although some white stones only had flecks of grey. There's probably not enough in the classroom to mine commercially but it was an interesting observation and the sort of thing that often sparks off an EE. Not sure that this would be such a good EE topic though.
Research Question: Is dirt magnetic?
Essay: Yes.
Inclined Plane
Posted on 24 March 2011 at 16:14h
I often think how unrealistic a lot of the physics that we teach at this level is. How many times do you come across motion with constant acceleration or a square block sliding down an inclined plane? Well I've seen one now. Due to my interest in rock climbing I know the position of every large boulder within a 10km radius of my house, so when one moves I know about it. Earlier this week the boulder in this photo was at the top of the hill, It had a very interesting overhanging front face. I even went up to try to climb it once but the landing was too bad, in fact there wasn't a landing just a very steep slope. When a boulder sits on an inclined plane the component of the weight acting down the slope is balanced by the friction acting up the slope. On Monday it rained a lot reducing the friction, the component of the weight was now bigger and the stone started to accelerate down the slope coming to rest on the less steep lower part where the forces were again balanced.
Well it would be nice if simple physics could be used to explain this event but it probably wasn't like that. The stone was actually sitting on a ledge made of loose stones and mud, the rain washed away the ledge allowing the stone to roll down the slope, an altogether more complicated problem. I really wish it had slid because then the interesting overhanging face would have a nice landing.
Desktop heater
Posted on 23 March 2011 at 15:05h
There was an interesting article in our local paper (Firda) this week about a man who has plumbed his computer into the heating system of his house so that he uses the heat generated to warm the bathroom. In the photo you can see inside the computer where water is being circulated round the processor. You can also see in the photo that the man is wearing a woollen sweater because all the heat that would normally be going to heat his work room is being transferred to the bathroom. He reckons that he saves about £200 a year and I'm sure he does save this amount of money from what he would normally spend to heat the bathroom but will spend an equal amount extra to heat his workroom. I hate to think what will happen when he comes to buy a new computer. Maybe if you buy the house you'd get the computer thrown in for nothing? It also says in the article that to maintain a comfortable temperature the computer must be active all the time so instead of switching to hibernate he gets it to solve long mathematical problems. I find it hard to believe that this is actually saving money, surely an electric heater is a more efficient way of producing heat energy than a computer, although I guess it all ends up as heat eventually. I wonder how much PE is stored in a HD.
Professor Splash
Posted on 18 March 2011 at 13:30h
During break some of the staff were talking about a video they had seen on the web about a guy called Professor Splash who belly flops into 30cm of water from about 9m (new record is now 11m). I thought this might be a good example of motion to discuss with my SL class. First they calculated his velocity on hitting the water and got about 13ms-1. Then, assuming the acceleration to be constant found the deceleration through 30cm of water to be 300ms-2. Wow 30g. He's a big guy so assuming his mass is 100kg then the force required to slow him down is 30,000N which if the area of his front is 1m2 (he has a bit of a belly and a big chest) the the pressure is 30 kPa or 3Ncm-2 . Well that's not much I think I'll give it a go. Of course there were rather a lot of approximations there including the old "constant acceleration" one.
Watching the video carefully you can see a couple of interesting features. Just before hitting the water he puts his hands out giving an extra 50cm of deceleration just before hitting the water. I guess his hands will be pushed against his body just before it makes contact with the water, his body is angled forwards so that even though his hands hit first he still hits the water flat. Having such a small amount of water in a plastic paddling pool might mean he is able to displace the water sideways instead of upwards but I haven't quite got my head around that one yet. Apparently the amount of water is important as is its temperature, I can't see the temp being so important as the change in density of water at different temps is actually not that much (1000.00 kgm-3 at 4°C and 995.68 kgm-3 at 30°C density calculator).
I almost forgot, probably the most important feature, the mattress under the pool.
Red sky at night shepherds delight
Posted on 17 March 2011 at 13:05h
Just been doing scattering with my HL class and was getting myself confused trying to explain the blue sky in the day compared to the red sky at sunset. I think I might have been mixing up to different effects, not that we have many sunsets in Norway at this time of year.
Firstly some facts about scattering, properly named Rayleigh scattering which is the scattering of light by small particles such as molecules in the air. The Intensity of light scattered at an angle ϑ is inversely proportional to λ4 so at large angles the intensity of shorter wavelengths will be greater. So when looking at the sky in the daytime you are looking at the light that is scattered at large angles from the suns rays.
The amount of light scattered increases as the light passes through more atmosphere so at sunset when the light passes through a lot of atmosphere more of the blue light will have been scattered than at midday, the light directly from the sun has no blue so the sun looks red. But what makes the sky look red? This is I think due to another effect; if there is a lot of pollution in the air the larger particles scatter the red light making the sky look red, this can also happen at midday if there is a lot of smoke in the atmosphere after a volcano or something. This effect is also made greater when the atmosphere is thicker hence is normally only seen at sunset (still not totally convinced by this last bit).
Fukushima
Posted on 16 March 2011 at 14:53h
There has been a lot in the press about the reactor at Fukushima that was damaged by the earthquake in Japan. The type of Reactor is not the same as the type that is in most text books so I did a bit of research so I would be able to answer my students questions. The type of reactor I normally describe to my students is a Pressurised water reactor that has a high pressure container surrounding the fuel, the fuel heats the water that is pumped into a heat exchanger that boils water used to drive the turbines. The Fukushima reactor is a boiling water reactor, the main difference is that the water used to cool the fuel is the same as the water that turns to steam and drives the turbines. This means that the water does not have to be kept at such high pressure.
When there is an earthquake the control rods are pushed into the fuel slowing down the chain reaction. In BWR tthe water also acts as the moderator so the rate of reaction can also controlled by the flow of water. When it flows slowly bubbles are formed in the gas which reduce its moderating effect so the reaction slows. A neat bit of feedback since if the reaction slows there isn't so much heat produced so the rate of flow of coolant does not have to be so great. Contrary to what I told my class yesterday the fuel does not have to be removed to stop the reaction as it should stop producing heat if the control rods are fully inserted, however it does take time for the fuel to cool down so water must be kept circulating until the temperature drops.
Tele-revision
Posted on 15 March 2011 at 15:33h
I've finished the syllabus, the trial exam is over and it's time for some revision. This applies only to my SL class of course since we won't finish the HL syllabus until the last lesson. So how can we revise in class. Going through the whole syllabus is quite pointless as is picking out random difficult bits. Going through past exam papers is Ok but only if all the students have tried the questions beforehand (forget that then). Getting students to do exam questions in class might be better use of the time but it's incredibly boring for me. So to fill the gap last year I made a compilation of interesting physics videos (or videos of interesting physics) from youtube. What we do in class is watch the clip and discuss the physics behind it using the physics learnt to explain these interesting phenomena is a good way to round off the course and is a nice way to revise without it feeling like revising. The other day we spent the class discussing the recent tsunami, during the hour long class we started with waves, energy of a water wave, refraction of water waves, relationship between wave speed and depth, v = fλ, seismic waves, refraction and reflection, how ultrasound works, how seismic studies work, the working of the ear, impedance matching, how a seismograph works, Newtons laws of motion, inertia, resonance. Then we got on to nuclear power, chain reaction. critical mass, moderation, control, transmutation of oxygen, nuclear waste, fuel enrichment shutting down a reactor. So we covered a lot but did it prepare the students for the exam. Well I hope so, explaining these things is exactly the sort of skill that will be tested by objective 3 type questions but more importantly maintaining an interest in the subject throughout the revision period will make the revision more meaningful and enjoyable, it also keeps me happy and if I'm happy we're all happy.
Tsunami
Posted on 12 March 2011 at 08:59h
We are all shocked by the news of the tsunami in Japan and are thoughts are with the families who have lost their loved ones and homes. Many of us teaching in international schools have students from the Pacific region which brings the suffering even more closer to home. After such a tragedy students will often want to understand what exactly happened so it's worth reading up on tsunamis so you are able to answer questions in class. I have done a bit of research and have found some interesting facts.
- When the tsunami is first formed by the disturbance of the sea floor it can have a wavelength of several hundred km and a speed of up to 1000kmhr-1.
- Even though the water is not shallow the long wavelength makes the waves behave like shallow water waves with a velocity = √gh (same as in the waves in a bucket practical).
- The energy loss as the wave spreads out across the ocean is related to the wavelength so the tsunami loses little energy as it spreads out, this is why there were tsunami warning as far away as Peru.
- The energy per unit surface area is related to the square of the amplitude.
- As the tsunami enters shallow water they slow down and their wavelength gets less. The energy in the wave must be conserved but the energy per unit surface area increases which results in an increase in amplitude, this is called shoaling and can be demonstrated in this applet.
The University of washington website has some useful information and animations
And some interesting maps from magic seaweed showing the predicted spread of energy and displacement.
Treadhill
Posted on 11 March 2011 at 14:02h
I was staying at a hotel the other week and thought I'd pay the gym a visit. usually just train upper body strength since that's what I need for rock climbing however the Gym didn't have any of the usual apparatus just a couple of treadmills so I thought I'd give one a go. I've never been on one before so didn't know that you were supposed to switch it on, as a result the first 5 minutes were very difficult as I tried to push the belt round with my legs (good training though). As I was pushing away I tried pressing all of the buttons and must have got the right one as the belt sprang into life and started moving on its own. It's amazing how easy it seems when not only is all resistance removed but the belt actually moves on its own. After another 10 minutes I got a bit bored moving my legs back and forth so begun to crank up the speed and also found out that you can change the angle. I'm not used to running but found it quite easy running uphill on the machine so got thinking about the physics involved. Where is all the energy going? I wasn't actually going uphill so wasn't increasing my PE, not getting any faster so no KE and there wasn't any friction (not since I switched it on at least) so no work against friction, the only thing I was doing was moving my legs. People who use these machines tell me that when you run uphill it is more difficult and you use more energy but why? A better version would be one where you run up the hill then the belt comes on and whisks you to the bottom again ready for a repeat performance, probably wouldn't work as a treadmill but there is a climbing wall version and I think this principle could actually be used.
Jetski
Posted on 8 March 2011 at 10:57h
Reading the article about the inflatable backpack made me think about the time I got avalanched. It happened on the mountain behind my house and it wasn't a big one but scary all the same. I was out alone and decided to board across a steep slope when suddenly a big crack appeared and the whole slope started moving downwards. After a couple of seconds it stopped and I dug myself out and ran away. During those seconds I noticed some interesting physical phenomena. When the snow starts to move it becomes fluid and you sink in it, hence the idea behind the "snow pulse", it also becomes impossible to turn. When boarding down a slope you turn by digging the edge of the board into the snow, to do this you have to be moving relative to the snow but once the snow also starts to fall down the slope you are travelling at the same velocity as the snow so can't get an edge to dig in. So here's my idea; all you have to do is restore your relative velocity which means you have to travel down the snow faster than the snow is moving. The force of gravity is not big enough to do this so you need some help. So leave the inflatable back pack at home and strap on a jet pack, the extra force that this provides will accelerate you down the slope enabling you to turn as before. I haven't thought about what will happen when you get to the bottom travelling at 200 kmhr-1 but its better than being buried.
Snowpulse
Posted on 7 March 2011 at 16:53h
Just got back from a workshop in Berlin where I met as always an enthusiastic bunch of teachers. On the plane I was flicking through the in flight magazine and found an interesting article on a new safety device for skiers called a snowpulse. It's a backpack that you inflate if you get in an avalanche and involves some interesting physics. The photo shows it inflated, you don't ski with it like that but if you get in an avalanche you pull a handle at it inflates. The gas cylinder doesn't hold enough air to inflate it but there is a valve that uses the venturi effect to draw air in from the atmosphere. Once inflated it not only protects the skiers head but also makes them float to the surface. The explanation in the magazine as that it dos this by increasing the mass of the skier. I thought it interesting that they got the bit about the venturi effect right but messed up the simple physics. This is common when students write extended essays, anything complicated is simply paraphrased but when trying to use their own knowledge to explain something they sometimes get it a bit wrong. I had a look at the snowpulse website where the explanation is that "the airbag raises the victim`s volume and decreases its density, it therefore increases its “floating” capacity in the avalanche." This sounds much more reasonable. The website also has some gnarly videos of people getting avalanched.
A bridge too far
Posted on 2 March 2011 at 12:53h
The weather wasn't kind and the snow project was cancelled due to lack of snow and all the ebay purchases have been stored for use at a later date. I guess we could have transported all the student to a snowy place but it would have been a big hassle so we went for the easier option of paper bridge building. Everyone agrees that team skills are important qualities to be successful in most areas of business so why don't we do more about them in schools? Traditionally I suppose these skills were developed in team sports but we don't do much of that at our school so I'd say we are a bit lacking in the area of encouraging teamwork. Having said that I'm pretty impressed with the way the students have worked throughout the day.
Trials and tribulations
Posted on 1 March 2011 at 19:51h
This morning my students sat their trial papers and this afternoon I marked them. I actually marked paper 1 before the students had finished paper 2, I just wanted to wind up the History teacher who was making the usual comments like "wish all i had to do was mark them right or wrong", "all right for some you should try marking this lot". Actually he didn't say any of this but they usually do. I always mark the mc papers by stacking them all up on a cork board then pushing a drawing pin through the correct answer. It's the fastest method I've found. Paper 2 isn't quite that quick (but don't tell the History teachers) this year was extra fast though since I had already done the whole paper when I made the exam answer section for this site. I gave my students May 2010 time zone 1. I tell my students which paper they are going to get so they don't do it by accident whilst revising. One thing that I noticed when adding up all the marks is what a big difference a high IA score can make (I always add in their IA scores to the trial exam to give a realistic grade). With a score in the 40's its possible to do quite badly on all the other papers and still pass.
Drip drip drip
Posted on 28 February 2011 at 09:50h
As the snow melts streams of water start to appear everywhere. This is nothing surprising so the roads here have very good drainage. Sometimes you can be driving along a road with water falls crashing down on one side and the fjord on the other, it's unbelievable how so much water can be directed under the road, I guess the amount of water in a waterfall looks much more than it really is. The two streams in the photo are not quite so impressive and how these are directed under the road is quite believable but they are interesting all the same. It's difficult to see in the photo after falling in a continuous stream the water breaks up into individual droplets. In really life this is easy to see but in the photo the droplets have become blurred so the stream looks continuous all the way down, however if you look closely you can see that at the top of the stream you can't see the background through the stream since the light is
refracted by the water however at the bottom of the stream you can since the stream is now made of droplets. If you look at the enlarged portion to the right maybe you can see what I mean. this in itself is interesting but it was the way the water turns from being continuous to droplets that I was most interested in. What seems to happen is that the water is accelerating so the stream gets thinner as it falls until it gets so thin that it forms drops. Hmm, that doesn't make a great deal of sense but it's a start. There seems to be a minimum "continuous stream" thickness, why do drops form when the stream gets thin? How is the rate of flow related to the distance the water falls before turning into drops?
The best laid plans
Posted on 27 February 2011 at 13:36h
As the snow melts and the forecast is for more rain the plan to use snow as the theme for our group 4 project seems less and less likely . A back up plan has been hatched so it looks possible that we will be indoors building paper bridges instead. Well at least the bridges will be useful for crossing the roads that are rapidly turning into rivers.
When the rain runs down the road it forms some interesting patterns, if there is too much it basically forms a river but if there is just a few millimetres you get an effect like the one I have tried to photograph in the picture. What you can just about see is a series of wave like features lining up down the road. What seems to be happening is the surface water is travelling faster than the water in contact with the road so overtakes it. This results in a build up of water which "breaks" like waves on a beach. As the waves progress down the road they spread out until the "waves" reach terminal velocity. When I was a teacher at Atlantic College in Wales, one of my students wrote an extended essay about this. I remember he struggled with recreating the waves in the lab and also found it difficult to measure lengths from photos like mine due to the perspective.
Jake the peg
Posted on 25 February 2011 at 15:01h
Last week it was fantastic sunny weather and I was able to go climbing outside for the first time this year. it was about -5°C so pretty cold but the friction on the rock is much better when its cold so was perfect, I just realised that I blogged about it a couple of days ago but never mind. The shoes in the picture are the sort I wear for rock climbing, they are smooth like slick tyres to increase the friction, so much for friction not being related to surface area then. The rubber is actually quite like racing tyre rubber except that it is made to have optimum friction at much lower temperatures. Oh and incase you are wondering I don't have 3 legs but carry an extra pair of shoes (one of them is still in my bag). Unfortunately the weather didn't last and it's started to rain, maybe going to have to cancel the Gp4 project on snow and either change the topic to rain or stay inside and build paper bridges.
Snow grain snow pain
Posted on 22 February 2011 at 20:03h
It may not look very impressive by I'm quite pleased with the photograph of snow grains though the 99p lens with my mobile camera. I think its definitely going to be possible to get some data on grain size by magnifying the snow next to a scale like I've done here. Apparently snow grain size is SNWG to those in the know. Today I went bouldering (climbing boulders). It was very cold but the friction between skin and rock is best when its cold, there is a limit though, I think less than -15 and it might not be possible to regain the feeling in ones finger tips ever again. Walking to the boulders over the snow I noticed how it is beginning to get soft again, when its really cold you can walk ontop of the snow but now the top layer is starting to give way. this means that you walk quite nicely for a while then suddenly a foot breaks through the crust and you almost dislocate a knee.
Spring is coming (in about 4 months)
Posted on 21 February 2011 at 16:40h
Nice weather today, blue skies and -12 until the sun comes up. As the days grow longer the intensity of the sun becomes noticeably more. In this photo of my neighbours houses you can see that the amount of snow remaining on the roofs is related to the direction they are facing. All the roofs are the same angle and since the snow fell on a fairly windless night originally had the same amount of snow on them. The air temperature hasn't been above zero so the only way the snow can melt is by absorbing energy from the sun (houses are well insulated in Norway so very little heat escapes from the inside). The roof on the left is pointing directly South so gets most sun and the one in the middle is pointing North so gets no sun. The sticking out roof above the balcony points West. It would be very interesting to measure the thickness of snow on a whole range of roofs, roll on group 4 project day.
EBay Physics
Posted on 19 February 2011 at 12:20h
The postman had to make his way down our slippery path to ring the doorbell this morning as the first consignment of our group 4 project equipment arrived. 14 magnifying glasses and 14 compasses all individually wrapped. The magnifying glasses seem great but some of the compasses seem to have become de-magnetised (easily fixed). I ordered these about a week ago from my favourite supplier E Bay. Over the years I have bought Nichrome wire, Neodymium magnets, spectrum glasses, potty putty, jumping footballs, and lots more. It's a great way to fill your cupboards. The magnifying glasses are advertised as x40 magnification and they do seem pretty thick but there's quite a lot of distortion around the edges so they work fine close to the eye but not so good at a distance a good example of how reducing the aperture size (by the iris close to the lens) reduces aberration. You can see in the photo how the magnification is greater towards the edge of the lens as well as a bit of chromatic aberrations.
Keep on skydiving
Posted on 18 February 2011 at 14:33h
A report of the meeting in October of the Gp4 Curriculum review group has just been published on the OCC . It's the first stage of the curriculum review process that will prepare the new subject guides for first examination in 2016. I've just had a quick read through thought I'd mention a couple of points. First about this statement "state of the art software developments have blurred the distinction between real and virtual investigations". Have they? I can still tell the difference between virtual and real, I thought this blurring was only in science fiction, "The Matrix" etc. I think that simulations are great for two things, firstly understanding theory and secondly modelling situations so that the underlying theory can be seen more clearly (pretty much the same as the first really). I do not think they should replace activities where students manipulate real physical systems. I have always thought that one of the points of doing practical work was to see the shortcomings of our simplified theory, a sort of teaser to further study. I have heard the argument that in "real physics" the experimenters are usually sitting at a computer screen while the action happens down the end of a 5km long tube, but we are not dealing with cutting edge physics we are trying to teach the basics and to do that surely its best to see the real thing. Why do people bother going skydiving when they can simulate it on XBox? Well they do and I want to encourage them to keep jumping out of planes.
The guy in the photo is one of my former students Jens Møller from Greenland, I think there is the odd sample of his work scattered about inside the site too.
Watch the skies at night
Posted on 17 February 2011 at 07:17h
Realising I was interested in applying physics to unusual situations a friend sent me a link to wired. The specific article was about the relationship between the frequency of a dogs drying shake and the size of the dog, interesting stuff. Further reading revealed several physics blogs including dot.physics where Rhett Allain investigates some unusual phenomena from floating mac books to spherical cows. Lots of interesting stuff and a good source for EE material. However if you are looking for EE material beware, the articles on this site don't just raise questions but also attempt to answer them, so a student might get a bit too much information. This can be ok, its good to compare ones own findings with those of others but a simple paraphrasing/ extension of one of these articles would not be good.
Another one of the articles I was pointed to was about comet Tempel 1 that was photographed by the passing Stardust Next probe on Monday. The pictures are quite something but I was a bit disturbed to read that in 2005 an 800 pound metal slug was fired at it.
From the home page of the wired site my attention was grabbed by the headline "Giant solar blast headed for earth". Lets hope for clear skies and a we might be in for a some spectacular Northern lights. I'll be out with my camera (mobile phone) to take some poor quality pictures.
Moire Christmas
Posted on 16 February 2011 at 16:43h
I was sitting in a meeting this afternoon and suddenly there was a bit of a swoosh and a pile of snow flew past the window. This is a common occurrence in Norway when the snow slips off the roofs. If you visit a city you will see signs warning that you are going to be hit on the head by snow falling off the roof. Its an interesting projectile problem when it happens, the first bit isn't going very fast so drops vertically, as the sliding snow picks up speed it falls further and further from the wall but not very far since the angle of the roof means that the horizontal component of velocity isn't that big. One of my students wrote an EE on it some years ago attempting to find a function for the distribution of snow.
I took this picture to illustrate the blog entry but when I made the image smaller an even more interesting phenomenon was revealed. Can you see the pattern on the wall in the middle of the photo? The wall actually is made of vertical planks. I think this is a sort of Moiré fringe due to the slight angle between the rows (or columns) of pixels in the camera and the planks. I will have to experiment with different camera angles to see if there is any change.
Deadlines
Posted on 15 February 2011 at 19:57h
Why is it that some students t
hink that a deadline is the time you are supposed to hand something in rather than the last possible time you can hand it in. I believe the word comes from an imaginary line on the battle field that if you crossed you would die. If my students were in battle they would all be standing on the line seeing how close they could get to the bullets. Well the IB learner profile does mention risk takers I suppose. maybe its time that education started doing what they do in most other walks of life to reward people that complete jobs ahead of time, pay bonuses. I don't mean paying actual money or anything but maybe awarding extra IB points to students who hand in early. I proposed this to a group of students but they didn't think it fair since some students need more time than others due to language problems. Hmm, hadn't spotted that correlation but point taken.
The not so Big Bang
Posted on 14 February 2011 at 15:27h
Astrophysics with SL again. Started by discussing Newtons static model of the Universe and they quickly got the idea that if the universe is static then it must be infinitely big and time must be infinite, one student then made an interesting observation. " remember what you said about the end fate of the universe being the point at which energy had completely spread out then there would be non temperature gradients so no work could be done? Well if time was infinite then we would have reached that state already:"
Good point.
After that I decided to build the universe in Interactive physics so set about arranging particles for the big bang. The students got a bit bored so I pointed ou that the original had taken 7 days so what's a few minutes when the result will be the most important event in history. The idea ids to group some particles in the middle of the screen, turn off gravity switch on electrostatic force the POW they fly apart. Completely fake of course but the purpose is to show that if you make any of the particles the frame of reference then all the others will move away from it. It worked last time as you can see here.
This time the force was a bit big and all the particles flew apart so quickly you couldn't see anything. Quite realistic really
Snow branch
Posted on 13 February 2011 at 13:45h
Another day another branch. The weather has been superb so today called for a longer walk with once again snow covered branches on my mind. The photo shows another interesting aspect of snowy branches, notice how there is more snow on the tree end of the branch than the tip. My first thought was that it was to do with the angle of the branch, there is more snow where the angle to horizontal is least. The night it snowed there wasn't much wind so the snow fell vertically down, the lower angle part of the branch would have presented a larger area then the steep part. On observing more trees I could see that maybe there was another reason, the branch is thicker at the tree end so maybe that's why the snow is able to pile up higher.
Snowed under
Posted on 12 February 2011 at 10:29h
The day after we decided to make snow the theme for our Gp 4 project it snowed, the project isn't for another 2 weeks so we shouldn't get too excited though. When we were discussing the project one of the other science teachers suggested that student might look at the bending of tree branches like the one in the photo (taken whilst walking the dog an hour ago). This is quite a complex problem, if the snow forms an even layer along the whole branch then the bit of snow on the tip will exert a greater toque than the bit at the tree end. Its the sort of complicated cantilever that engineers love to get to grips with, the solution would almost certainly involve a differential equation and would be a great investigation for an extended essay but is maybe a bit complex for a Gp 4 project.
How did they do that?
Posted on 11 February 2011 at 11:46h
Today I was teaching about binary stars to my second year SL class. It's often interesting to think about how some of these discoveries were made without the help of modern technology, In the case of astronomy the Greeks simply looked at the stars but by the early 1900 astronomers looked at photographs of stars. What Henrietta Leavitt ( I wonder if she is related to Randy Leavitt the famous climber?) did was to first take a photograph of the stars, this would be black dots on a white background since the photo plate turned black when exposed to light. The size of the dots is related to the brightness of the star but how did she notice which ones had variable brightness? What she did was to make a positive out of the negative and lay it over the original. The effect is that the black and white dots cancel each other out and you get a totally black sky unless one of the dots has changed size. I thought I'd try to simulate this using paint, it works quite well I think.
Not over yet
Posted on 9 February 2011 at 15:15h
Sometimes I just can't get things out of my head like this problem with the minimas in sound intensity around the room, they are definitely there, I heard them. They are about 20 or 30cm apart so if you move your head from side to side you hear a couple but according to the theory they shouldn't be there or at least if they are (with the lower notes) they should be further apart. What I normally do at times like this is look for a simulation so I can see what's going on. Paul Falstad's ripple tank is a good place to start. So I set up two sources about 1/2 a wavelength apart and got the result on the left, a bit of cancellation in the line of the sources but not complete, certainly no minima and maxima.
I tried adding some walls to see if I'd get any cancellation but all got was this. Hmm, maybe there are some areas. I think I'm going to have to try it again in the class room.
Don't think
Posted on 9 February 2011 at 14:19h
The other day I got my students moving there heads around whilst I played the same note through the speakers of my laptop. If you try it you can hear a marked difference as you move from a quite loud spot to a quite one. It seems to due to the interference of the sound waves coming from the speakers like Young's slits for sound. I thought it would be nice to turn this into a class practical so set about playing with possibilities. I tied an equal length string to the position of each speaker and walked around my study listening for changes of intensity, I was hoping to measure the path difference at my ear using the string and then find the wavelength, repeat for different values of f and you've got a graph that can be used for assessment lah de dah. I thought I could do this with a whole class by simply giving each student a pair of strings that were attached to my computer, I can imagine it could have been fun if I hadn't started to think.
Lets take a typical frequency 660Hz, this gives a wavelength of 50cm, my speakers are about 25cm apart so the only place that there will be destructive interference is in line with the speakers so what's causing the loud and quiet regions that the students (and me) were hearing, were we simply imagining it because that's what we expected? Or was it due to interference between the sound and the reflection off the walls?
Head bangers
Posted on 7 February 2011 at 14:05h
Its amazing what you can get students to do, today I got them to put one finger in an ear and shake their heads from side to side. The point of it was to listen for minimums and maximums in sound intensity due to the interference of sound from the two speakers in my laptop. I used the phet fourier transform simulation to produce the sounds and it worked really well. The sound isn't very loud so there wasn't much of a problem with reflection off the walls, The higher the note the closer were the minima. Could probably base a really good practical on it but I don't think it would be so good with 15 students trying to do it at the same time. maybe In could set up my computer at the front and everyone could take measurements on the same sound. Hmm I think i'll get to work on it.
Bath time
Posted on 6 February 2011 at 19:30h
I've just been marking some of the reports my students have written about the "resonance in a bucket" experiment. The idea is that they measure the velocity of shallow water waves travelling back and forth across a carton. It reminds me of being in the bath when I was a child. I used to like swishing backwards and forwards making waves travel up and down the bath. The problem was that if you got the right frequency resonance occurred and the bath water spilled over the end of the bath making its way through the kitchen ceiling (In Britain many houses do not have waterproof floors unlike Norway where bath time is much safer). The wave in the carton has a speed that is dependent on the depth of water, once the side is pushed the wave travels across. The question is; "is the speed of the wave dependant on the size of the push?" If the wave was a ball then it would be but since its a wave I don't think it is. Its hard to believe that the speed of the wave is not influenced by the person pushing, it seems like you could make the frequency whatever you like but you can't.
raining in silicon valley
Posted on 4 February 2011 at 10:58h
Now it's raining again so I'm glad that got a new jacket for Christmas. My old jacket was 15 years old and although still sort of functional was looking a bit warn out. The new one is a top of the range Bergans jacket with all modern features. I am amazed at the progress in this time, my new jacket has been designed the old one was sewn. The hood on the old one was like putting a bag on your head the new ones hood is like a hat, the biggest news however is the material it's made out of, the water simply runs of it. This is particulary noticeable when I take the coat off and give it a shake, this would have no effect on the old coat but the water flies off the new one leaving it almost dry. Apparently its all to do with silicon, what a useful element this seems to be.
The VSBT
Posted on 3 February 2011 at 18:30h
Today I was teaching some Astrophysics to my SL class. I made a binary star with interactive physics and they thought it was out of this world (haha). I am always amazed by how much we know from such little information, take the Cepheid variable for example. Watching documentaries on TV you might get the impression that these are quite impressive flashing lights in the heavens rather like the flashing Christmas tree lights that my wife bought by mistake this Christmas. The reality is rather less impressive as can be seen on the video from the Hubble site. Focusing in on that tiny dot for several days and you see some sort of variation in brightness. I read in the paper that there are plans to build bigger and bigger telescopes its just a pity that they have run out of imaginative names, two of the new ones will be called; TMT- thirty meter telescope and ELT- extremely large telescope, do they lack imagination or are they being ironic?
I've got a VSBT - very small broken telescope.
On the pull
Posted on 2 February 2011 at 10:58h
Last post I mentioned that we have a Gordon setter, his name is Ben and he keeps me sane by making me get away from the computer to go for walks. He is our first dog and we have not managed to train him very well and one area we have failed in is teaching him to walk nicely on the lead. I already had long arms before we had Ben but now they are even longer, there is one advantage though and that is when going uphill. A couple of years ago read a book about fell running (Feet in the clouds) and for a while I was inspired to run up mountains, naturally I did this with Ben who loved to pull me upwards. What I didn't like to admit was how much my times were affected by this upward force, I thought it must be due to my natural fitness but when I tried without Ben my times were no where near so good. Would make an interesting investigation.
Do the Shake and vac
Posted on 1 February 2011 at 15:44h
The dog hair in our house acts a bit like the lycopodium powder in the classic Kundt's tube experiment, it seems to accumulate in places where the air is undisturbed like behind doors and under chairs. When we bought Ben we read in a book that Gordon Setters don't lose their hair, THIS IS A LIE or else someone keeps sneaking into our house at night throwing in handfuls of black dog hair. Because of the dog hair we have to vacuum quite a lot so we have several small vacuum cleaners strewn around the house like the one in the photo. When ever I plug the vac into that plug the circuit breaker switches off, however I discovered that if I reduce the speed of the motor before I plug it in then the circuit breaker doesn't pop, once started I can turn up the speed and hoover away. It's a classic example of back EMF, when the motor coil isn't turning their is no induced EMF to oppose the increasing current so the current flowing through the coil is large, large enough to pop the circuit breaker. The speed control is probably a potential divider which reduces the PD across the coil and hence the current. The thing I don't understand is why the manufacturer added the speed control. Maybe they were expected problems with circuit breakers as this is the only time I turn it down from full speed.
What's real
Posted on 31 January 2011 at 18:48h
Apparently, in the film 2012, the world is destroyed by neutrinos which is interesting because if they could then they already would have given that we have in the order of 1014 of the things passing through us every second. If Hollywood are going to make up physics then I wish they'd make it all up rather than mixing the made up with the real. The Science and Entertainment Exchange, an advisory body run by the US National Academy of Sciences, don't like this distorted science either and would like Hollywood to stick to the facts. Just imagine if it was reversed and Hollywood tried to tell us that they would like us to teach the physics they portray in their films instead of the real stuff, hmm.
More is more
Posted on 30 January 2011 at 09:35h
Yesterday evening I watched a re-run of a Top Gear programme where Richard Hammond races a ford mustang against a G-wiz electric car. The first run with normal power is predictably won by the mustang but then they put in 10 times more batteries and the electric car wins. To get more power the batteries must be connected in parallel so that the pd is 10x bigger, this would give 100 times more power (V2/R) but wouldn't it also burn all the wiring and the motor. I guess that's why this version of the car was radio controlled. The extra weight of all the batteries might also be a problem. I have a friend who helped set up the cameras when Top Gear did a race between some climbers and a car driving up the Verdon Gorge, he said it was a complete fix, maybe this is too. Got to be careful where you get information from.
Ripples in the cosmic ice cream carton
Posted on 28 January 2011 at 12:17h
My first year classes have been trying out one of the new practicals "resonance in a bucket". I've been looking for a good waves practical that doesn't rely on knowledge about standing waves ever since that went out of the syllabus. In this experiment a wave is sent back and forth across a plastic box. This ties in nicely (or gets students confused horribly) with SHM, since this isn't SHM its a wave travelling back and forth with constant velocity. The students seem to see this practical as something to do with oscillations and saw the time for two crossings as the time period rather than the time taken for the wave to cross the box twice. When asked to calculate velocity they didn't immediately see that the distance travelled for 10 "cycles" was 10 x the width of the box. Interesting how students find it difficult to change their train of thought.
Some of the results were very good by the way.
Completely wired
Posted on 28 January 2011 at 11:52h
Yesterday I decided to do another design experiment with my second year class. This is hopefully the last. I don't say hopefully because I don't like doing them but because I think its time to start concentrating on the exam. Anyway the theme was NiChrome wire. I bought 20m of 5 different diameter wire from Ebay last year and have been saving it for a special occasion. The idea was that the students would devise a research question related to the wire. There were quite a few interesting ones but I'm not going to write about them here because some of my students haven't exactly finished (started) yet. I think it was a successful theme but there was one thing that I had not foreseen. The wire was delivered in a loose coil not a spool, as soon as the coil was released it went haywire (so that's what haywire means) as you can see in the photo. Next time I will wind the wire onto spools before the lesson.
Ripples never come back
Posted on 27 January 2011 at 07:16h
When I was at university my favourite band was Genesis , in fact I rarely listened to anything but Genesis. My love of the band had an abrupt end when Peter Gabriel left however the new light version still had a couple of good tracks one of which was ripples. It was the ripples in the fjord on the way home yesterday that reminded me of the track. There are always interesting difficult to explain patterns on the fjord like the one here. Is that gap in the waves due to interference or is it something with reflection of light? The patterns look very much like the sort of things you get in a ripple tank (simulation).
I looked up the lyrics for ripples;
Look into the pool,
Ripples never come back.
They've gone to the other side.
I dive to the bottom and go to the top to see where they have gone.
Oh, they've gone to the other side
Hmm.If its a pool then the ripples do come back because they reflect of the other side and why were they diving to the bottom to find out where they had gone, ripples are surface waves. Ding goes the TOK bell.
True Grit
Posted on 25 January 2011 at 15:13h
I may seem to be a bit obsessed with the weather and its effect on the roads at the moment but you have to realise I walk to and from work about 4 times a day so spend a lot of time thinking about it. When its pure water ice there is so little friction that its simply impossible to walk unless the road is completely flat (not common in Norway). The only hope is that the council has spread some grit on the surface and this make an incredible difference, even just a few grains. I suppose its because the pressure under a few grains will cause them to really bite into the ice. Might be interesting to study the relationship between the number of grains and the frictional force. Pity EE's don't start until after Easter.
Ice-shrooms
Posted on 25 January 2011 at 11:20h
We have had snow on the ground for the past 2 months but its now starting to melt. This has been helped no end by the fact that it has been raining for a week. Walking to work I spotted a couple of these strange ice mushrooms which have formed underneath accumulations of grit. It seems that the the grit hhas protected the ice from the rain preventing it from melting. Its like speeded up geology.
The view from here
Posted on 23 January 2011 at 13:45h
I started teaching the astro option to my second year SL class last week and discovered something interesting. Very few students (and I guess very few people in general) know that the planets are not fixed in their position relative to the stars but move around on a sort of spiral path. However they all knew that if you were to look at the solar system from a long way away you would see the planets orbiting the sun. So students know what the solar system looks from from a place that no one has ever been to but do not know what it looks like from home. That struck me as quite odd but is a nice example of how we get knowledge, not from our own observation it seems.
Stop detractors
Posted on 22 January 2011 at 16:02h
I've just completed the 57th online multiple choice quiz, that's 570 questions with 3 more to go so that the whole core and AHL is covered. After a while you start to get a bit obsessed with multiple choice and begin to think entirely in terms of 4 choices, the problem is that not everything has 4 choices so you have to make up some stupid ones
Shall I eat that piece of pizza?
A. Yes
B. No
C. Cow
D. Frog.
However if using multiple choice questions to test knowledge having 2 stupid choices narrows it down to one of two possibles either yes or no which means that a student could get 50% by choosing randomly, that's why question setters have to make up detractors which makes the job that bit more time consuming. I think detractors in questions like the definition of momentum is........are fine, but when the answer is a number I think they are unfair, they lead the student to believe that they have got the right answer when in fact they have made a simple mistake. So I have abandoned numerical detractors which has certainly made my life easier. Maybe I should start a campaign, stop detracting our students.
Met with septicism
Posted on 20 January 2011 at 15:01h
Do you see that bit where the snow has melted well that's our neighbours septic tank, actually it's the flat rocks that cover the top of it to be more exact. The reason the snow has melted is due to all the heat that is released from the tank. Some of this is due to the hot water that is flushed through it every day but some must also be due to the chemical reactions that are taking place as bacteria break down the stuff inside. Its bad when the water coming to the house freezes in the winter but much worse when the septic tank freezes, fortunately this is more rare which I guess is because of the hot water and heat producing bacteria. Its a pity all this heat goes to waste, it would be much better if the septic tank was inside the house, or maybe not.
Negative skates
Posted on 19 January 2011 at 13:55h
I always wanted a pair of roller skates but as far as I remember I never got any, as a result I am not very well practised at walking around with reduced friction between my feet and the pavement. I have already broken one ankle when I slipped on the ice on the way to work and don't intend to break the other so I am contemplating the purchase of what Norwegians call brodder and what I call Granny crampons. There are two main types the ones with spikes in them, which seems like an obvious way to stop the feet slipping, and the ones that are springs as in the picture. The thing that interests me is how anyone found out that wrapping springs round your shoes stopped you falling over on the ice, what will they think of next.
Launch party
Posted on 18 January 2011 at 16:19h
Well today the website went live so hello to anyone who has just been redirected here from the old site. I guess I should be having a party but there's no one home at the moment so I'll have to put the celebrations on hold. The problem is I'm not really finished yet, still trying to think up multiple choice questions then I've got the rest of the past papers to wade through. If you can't afford the 150 quid then you'll have to make do with the old site which is still hosted on the school server. Seems ages ago since I made the original.
Star bright
Posted on 17 January 2011 at 14:22h
I've been noticing a very bright planet visible in the South east every morning for the past couple of weeks so apparently its Venus and the one in the evenings is Jupiter. On Thursday I started my journey from Flekke to Cardiff to attend a meeting about setting up an online physics course, to cut a long story short i was still travelling on Friday morning and was able to see Venus from the plane. It was just before sunrise and was the only thing visible in the morning sky the rest being lost in the emerging blueness of the suns scattered light. it was such an impressive sight that I took a photo with my phone (switched onto flight mode of course). As you can see the photo is not very impressive although you can just make out the planet, its at about 2 o'clock. How is it that to my eyes the planet looked very bright but on the photo its not? A fweek ago i was commenting that when one takes photos of the aurora the result is usualy more impressive than reality this is the opposite. I guess its something to do with the non linear response of the eye (sounds convincing anyway). I don't know how the ancient astronomers judged that some stars were x times brighter than others I can tell which are brighter but struggle to say how bright.
I thought I'd try to zoom in on Venus to see what is revealed. The result is quite interesting although being colour blind I might lose some of the subtleties of the image. One of my students this year has written his EE on how to use a digital camera to measure the intensity of light from point sources like this. Here you can see that there is infact guite a lot of information to work with.
Time to start revising
Posted on 10 January 2011 at 12:13h
The holidays are over and its time to start the process of revising first for the trial exams then the real thing. That's not to say that I have finished the course because I haven't. I always hope that my students will have started revising over the Christmas holidays but this year I've been doing it for then in a series of over 50 multiple choice quizzes that will lead them right through the course. They shouldn't be thought of as practice for paper 1, they're much more than that. They are a set of structured questions that are designed to test a students knowledge on every part of the course. Each question has a properly explained answer so students should learn from their mistakes and there are a lot of animations to help.
Here is a free example Waves
Aurorasome
Posted on 6 January 2011 at 10:25h
Last night I saw the Aurora Borealis. It was nothing like this picture by one of our students (Matthew Enger) of the aurora over the college last year. Photos usually look better than the real thing as the camera takes in more light that our eyes, especially if a long exposure is used however last night was particularly poor due to that fact that the sky was completely covered by cloud so all I saw was a slight glow towards the North behind the clouds. Coincidently yesterday I got sent a link to the NASA website with an article about the Aurora. Actually it's not really coincidental as reading that was probably what made me look up last night instead of keeping my eyes fixed on the icy surface of the road. How is it that even an institution like NASA can write sentences like "energy stirs up the particles and energy trapped in Earth’s space". Hmm
Flushed with success
Posted on 3 January 2011 at 11:08h
Last week our water froze which means we have to carry in water and flush the toilet with a bucket. It's amazing how much more efficient the real flush is compared to using a bucket. I have experimented with all angles and flow rates but I can't beat the hundreds of years of design that went in to the WC. The reason we have no water is because the temperature has been down to -18°C and the water froze in pipe leading to our house. The interesting thing was that the water didn't freeze when it was -18°C but some days later when the temperature rose to about -1°C, apparently that's the way it always is (Why does everyone always tell you these things after the event) which is quite strange. Why should the water freeze when the temp rises? the only explanation I have is that its to do with air currents but that's as far as have got. I can see an EE coming out of this. The only alternative explanation I have heard was that the rising temperature forces the coldness back into the pipes but I'm not saying who it was that said that.
Snow shoes
Posted on 3 January 2011 at 10:52h
I bought myself a pair of snow shoes and have just been out on the hill to try them. When buying snow shoes you have to get the correct length, this is calculated on your weight, the heavier you are the bigger area shoes you need. Bigger area also means more expensive so I am lucky that I fall into the lightest category. There's quite an overlap in the sizing chart though from 54 to 91 kg you should use 25 inch shoes but from 77 to 114 kg you should use 30 inch. Quite a big uncertainty!
Two clocks
Posted on 19 November 2010 at 15:03h
I was chatting to another physics teacher, Chris Folland, at a workshop in Malta the other week. We were talking about how we physics teachers like neat solutions to simple problems and he told me about a really neat idea some of his students came up with. It's a way of accurately measuring a time with two stop clocks. Its so good that you could do a g experiment with drops of as short as 50cm (maybe less) and still get a good result. You need two students one starts clock 1 when the ball is dropped the other starts clock 2 when the ball lands. They then put the clocks together and stop them at the same time, the difference gives the time of the drop. Neat.
Lollipops
Posted on 19 November 2010 at 14:51h
Not exactly a lollipop but it is ice on a stick. I've noticed this phenomenon for many years and often wondered what caused it. On cold mornings , even when there isn't frost on the ground, large crystals of ice grow out of small twigs. The only explanation can think of is that the twig contacts squeezing sap out of small pores (twigs have pores I think) as the liquid squeezes out it freezes. Well not much of an explanation but its all I can think of.
Chernobyl on Wheels
Posted on 19 November 2010 at 14:38h
The Guardian again but this time an article about transporting of nuclear waste. It's said to be like "Chernobyl on wheels" by some observers but Chernobyl was a rather outdated nuclear power station and this is spent fuel rods so not quite the same thing.What interested me most was the photograph (which wasn't explained) that accompanied the article. It looks like there must be radiation coming from the container and indeed there is radiation, IR radiation.
Fast Orbits
Posted on 18 November 2010 at 09:35h
I was reading the weekly Guardian and noticed an article on the International Space Station that said it orbited the earth 16 times an hour, thought this was a bit fast and it is. The actual rate is 16 times a day. I'll use this with my class when we do orbits.
i dough
Posted on 3 November 2010 at 12:11h
last week I visited the local toy shop to buy some play dough and was interested to find a new version called idough, obviously cashing in on the iphone/ipod generation, well it worked on me and I bought 12 pots. Its actually just the same as play dough, squashy stuff made of oil flour with a strong salty taste. the high salt content gives it a measureable resistance so it can be used for electrical experiments. I set about designing a DCP practical using the dough but found that the resistance jumped all over the place. The best results were achieved by squashing a sample between the plates of a variable gap capacitor which hasn't been used since capacitance came off the syllabus (ok I know its back on now). The experiment worked quite well but the results were not as expected. Since my students might be reading this part of the website i'm not going to reveal all here's the worksheet.
Wood Chopping
Posted on 2 November 2010 at 16:00h
As one of my CAS activities with the students (all teachers are involved with CAS in UWC schools) I cut wood. If no one cut down trees around the college then we would be overrun with them so its environmentally sound. The wood is cut into logs sold to teachers and burned on their wood burning stoves so they can heat their houses with a renewable source of energy instead of electricity which in Norway is all produced from hydro hmmm.
Anyway, there is an interesting bit of physics in wood chopping. The best way to split a log is to first set the axe into it then turn it the other way round and hit the blunt end of the axe against a big log (as shown in the photo). This uses the momentum of the log to split it rather than the smaller momentum of the axe head. But according to newtons 3rd law the force on the axe should be the same as the force on the wood so how come the wood splits more easily when hit in this way?
I reckon its because when the stump is hit the way shown it is the axe that is slowing down the log so the force on the log is large. When hit the other way up the axe is slowed down by the log which requires a smaller force since the axe has a smaller mass than the log. The force on the tree stump is the same in each case.
Paint the rooftops white
Posted on 2 November 2010 at 06:52h
I've always thought that a way to combat global warming would be to paint all the rooftops on the earth white (or silver) this would increase the albedo of the earth and reduce the temperature. I present this as a bit of a joke to my students who always think its a crazy idea but I read today that it has some serious followers although the idea is a bit more sinister. Depositing shiny metallic particles into the stratosphere is the idea, this would have the same effect as the white rooftops but is more difficult to reverse. What if the result was not as expected?
Driving a formula 1 car
Posted on 1 November 2010 at 16:49h
Top gear is one of my favourite programmes in fact it's one of the few programmes that I watch apart from "master chef and "coming to dinner". In Norway we don't get the up to date programmes but lots of re runs however I didn't see them first time around so that's ok. Recently I saw an edition from about 2 years ago where Richard Hammond tries to drive a formula 1 car. The problem is that its impossible to drive slowly. Formula 1 cars are pretty light so the friction between tyres and road is small (F=μN) however their design is such that when they go fast the air pushed them downwards increasing N and hence the friction. This reminds of my first winter driving on the snow covered roads of Norway when I tried to follow a bus round a corner and ended up in a field.
Slinky
Posted on 28 October 2010 at 20:29h
I was doing a design lab with a slinky today. Students have to come up with a research question related to a slinky spring. always like the students to choose something different so as the lesson progresses it becomes harder and harder to get one that I accept. One group investigated the relationship between the frequency of the oscillation of a vertical slinky and the displacement of the end. I of course thought that the frequency would be constant but it turned out to be linearly related. The only explanation is that its something to do with the fact that the slinky is oscillating under its own mass so doesn't behave like a massless spring with a mass hanging on the end. I think I am going to have to try this one myself.
It reminds me of a recent discussion on the OCC about whether design experiments can encourage students to learn wrong physics. I think they simply enable student to see what the reality is like. All the experiments that we set up for them are incredibly contrived so that they show just the thing we want them to.
Neurosky
Posted on 27 October 2010 at 17:12h
I like to keep up to date with the use of technology in the classroom but I was just reading an article in the Guardian weekly about the latest developments in the game world and it bought it home to me how far education is from the cutting edge.
Apparently there is now an interface called a "Neurosky" that allows the gamer to control the game directly with their brain. If they concentrate they can blow things up or if they relax they can make objects float.
Next they'll be making us imagine things when we are asleep, dream on.
Polarisation
Posted on 8 December 2009 at 17:01h
Was doing polarisation with my class and unusualy for me I did a couple of real demos rather than simulated ones. First I did a demo passing a laser through some sugar solution placed between crosses polaroids. Not exremely convincing, would have been better to put the solution into a glass cube rather than a beaker. The other demo was looking at a piece of perspex through a polaroid filter, the perspex was held in front of my computer screen to provide polarised light. Students liked this one as you can see. They liked the hologram of a dog even more, pity this isn't on the syllabus.
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