Buoyancy

The Simple English Wiktionary has a definition for: buoyancy.

In physics, buoyancy (lit: float force) (pronounced /ˈbɔɪ.ənsi/) is a force on an object making that object rise or move upward. It comes from the Spanish word for "float", boyar. Buoyancy is made by the difference in pressure put on the object by the Fluid or air that the object is in.

The net upward buoyancy force is equal to the magnitude of the weight of fluid that is displaced by the body. This force enables the object to float or at least to seem lighter. Buoyancy is important for many vehicles such as boats, ships, balloons, and blimps.