Question

Give reasons for the following,

Giant hot-air balloons rise up.

Answer 1

Giant hot-air balloons rise up

1. The force which is responsible for a hot air balloon to rise is the buoyant force.
2. All liquids and gases in the presence of gravity apply an upward force called buoyant force on any object.
3. Hot-air balloons can float in the air due to the force of buoyancy.
4. Since the balloon is heavier than air, it should be filled with a large volume of much lighter things—either hot air or a light gas such as Helium.
5. Because the combined weight of the balloon and the gas the balloon is less than the weight of an equal volume of the surrounding air leads the balloon to rise.
6. So, we notice that hot air balloons have hot air inside and hot air is less dense than cooler air that surrounds the hot air balloon.
7. This means hot air is lighter than cold air.
8. Hence, due to buoyant force, the balloon rises.