How Does Buoyancy Lift a Balloon?

Since air pressure decreases with height, air presses harder against the bottom of a balloon than against its top. This difference in pressure creates an upward push. As long as this upward force is greater than the balloon's weight, the balloon will rise. But as it rises, the density and pressure of the air around it decrease, so the buoyant force decreases too. When the balloon reaches a height where the buoyant force equals the balloon's weight, it stops rising.

Hot-air balloons use heated air to provide buoyancy, because warm air is less dense than cool air.

(Rev. 1/9/99)