|MadSci Network: Physics|
Hi Ruth, A hot air baloon rises because the density of air in the balloon is less than the density of air outside it (Density is essentially the number of particles of air in a given volume). When that happens the balloon floats upwards. If your question was how the density of the air in the balloon gets lowered when it heats up read on... When air is heated, the particles of air gain energy. When that happens they start bumping into each other and trnasferring their energies between themselves. So the particles in the centre will start to push the surrounding particles outwards while those outside will continue moving outwards since they have no other particles to collide with. So the same number of particles will now occupy a larger space and hence have a lower density. I hope you have understood what I meant to convey. If not please do write back to us and we'd be glad to help you out. Cheers, Nauzad
Try the links in the MadSci Library for more information on Physics.