Planes fly because of the shape of the wing. The wing on an airplane is curved on the top side and flat on the under side. When air moves over the wing it causes the air to move faster over the top of the wing than under it. This causes negative pressure on the top side of the wing. Since air wants to move from a place of higher pressure to a place of lower pressure it causes a lifting or a ‘vacuum effect’ which creates lift on the wing allowing the plane to fly.