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.