The Physics of Hot Air Balloons

     A hot air balloon is a large bag filled with hot air or gas that allows it to rise. Although hot air or gas helps the balloon rise, physics is behind it all. The physics that deals with a hot air balloon is called buoyancy. Buoyancy allows certain things the ability to float in water, air, or any other fluid. The way buoyancy works with a hot air balloon is the upward buoyancy force is equal to the mass of the cooler surrounding air that is displaced by the hot air balloon. Therefore since the air inside the envelope is less dense than the surrounding air, which causes buoyant force because the cooler surrounding air is greater than the heated air. Although floating a hot air balloon is not so simple. When flying a hot air balloon the atmosphere will change depending on how far you are from earth, which causes a change in pressure. Along with that gravity has a part in flying a hot air balloon too. Gravity will pull the air molecules down which creates more molecules in the air. But buoyant force keeps the balloon lifted by using the air molecules to keep the weight equal.