The host of bubbles that come off photosynthesising elodea can be more or less impossible for students to count. iPads solve the problem. By using iMovie a film of the experiment can easily be obtained – the students can then count the bubbles from the film. At low light levels this counting can occur directly from playback – still better as the students are able to be far more certain of whether they have seen a bubble or not. At higher light levels where oxygen bubble production is more vigorous it is better to use frame by frame analysis to do the count. This degrees a degree of accuracy which simply isn’t possible with the naked eye or with ordinary ‘on-phone’ video applications. Whilst it is possible to do the experiment where the gas is caught and measured – this approach is rather faster and more fun.
Other similar uses might include speed measurement; assessing acceleration and checking he rates of reaction of metals such as tin and zinc – in the latter case you may want to use an app that allows you to mark bubbles as they are counted.