I forgot to buy the plasticine for the measuring density experiment I always do at the start of the course. I forgot last year too so used potatoes. This wasn't particularly successful so this year I decide to use balls of aluminium foil. They are a bit rough but that's the point of the experiment. The balls also contain some air so I expect a value of density lower than the actual value. It will be interesting to find out how much air is in the balls. One thing I like about this alternative is that the experimental value can be compared to the accepted density of aluminium. It was interesting making the balls, doubling the side length of square of foil results in 4 times the area and 8 times the volume but the volume doesn't look that much bigger.