While all the biology and ESS students were away on a field trip I decided to organise a practical morning for my EE students. It's one thing to have an idea but until you start to experiment its difficult to know what to expect. Here are a few of the questions of the day. Mazen, researching the resolving power of lenses was interested to know how the aperture size is adjusted as a zoom lens is zoomed. Antonio noticed some interesting effects produced when a magnet is held close to a vibrating guitar string. The uneven oscillation produced seems to split the frequency of the harmonics resulting in beats. Tim wants to know which what caused gear systems to lose energy, seems like its all to do with slipping as the cogs mesh. Filip tried to build coupled pendulums with Algodoo but they don't seem to work in 2D, maybe springs are better. Wassim is interested in how a robot is programmed to compensate for the state of the batteries. The first stage is to find out how the terminal pd of the battery changes with time. This involves measuring the pd as the batteries run down. This could take a long time with no load being lifted by the motor, maybe I should've told him.