buoyancy

Everyday

1. (science) The upward push that water (or air) gives to an object, which makes things float or feel lighter. tree →
2. The ability of something to float: «Cork has great buoyancy.» tree →
3. Cheerfulness and the ability to recover quickly from bad times: «her buoyancy of spirit». tree →
4. (money) When prices or business stay high and strong. tree →

In the lessons

In science lessons buoyancy explains why boats float and stones sink: an object floats if the upthrust of the water is as big as its weight. Salty water gives more buoyancy, so floating in the sea is easier than in a pool. Swimmers use buoyancy aids (armbands, floats). Related: upthrust, float, sink, density.

Examples

• Buoyancy keeps the boat afloat. tree →
• A life jacket gives you buoyancy in the water. tree →
• It is easier to float in the sea because salt water gives more buoyancy. tree →
• We tested the buoyancy of different fruits: the orange floated. tree →
• Submarines change their buoyancy to dive and rise. tree →
• Despite losing the match, the team's buoyancy returned quickly. tree →
• The buoyancy of the air made his heart light. tree →

Note

Say «BOY-un-see» (UK) or «BOO-yun-see» (US). Spelling trap: «buoy» comes first (u before o). Adjective: buoyant. Myth: heavy things can float if their shape pushes away enough water — a steel ship floats.