Posted on 05 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.