The Benouilli effect, used by aeroplanes, race cars and of course blowing pieces of paper. OK, In the case of an aeroplane wing, the air flowing over the top of the wing has a greater distance to travel than the air flowing under the wing, therefore the air travels faster over the top and has a greater Kinetic Energy. The gain in Kinetic energy comes from a loss of Gravitational Potential Energy, (I think it's GPE, at least that's what my teacher fobbed me off with). It is this drop in Gravitational Potential Energy that (somehow) causes lower pressure on top of the wing and therefore the aircraft is pushed up by the higher pressure from underneath the wing. These are the bits I need explaining: * Why does a drop in GPE cause lower pressure over the top of the wing. * If there is a drop in GPE, then surely the air will be lower than it was before, but it isn't, it's still at the same height (ie: the height of the top of the wing above the ground). * Why does the GPE decrease? I understand that the energy must come from somewhere, but why GPE? * Also, I have trouble applying this example to other situations, for example, blowing over the top of a piece of paper. Try this yourself, get a piece of A4 paper, hold it at two corners that are next to each other (it's better if the corners are close together), and blow, gently, just over the top of the paper. Unless it's very thick paper, it should rise up due to the Benoulli effect. Well, where is the GPE loss here? You give it the KE needed by blowing the air. If you can think of any other uses for the Benouilli effect, feel free to keep them to yourself. Alternatively you can write them down on a piece of paper, screw it up, then throw it away. Joke. But seriously, if you can answer all or part of this question, please respond.