While 'buoyant' often relates to water, it can apply to any liquid or gas where something can float. The helium balloon was buoyant in the air.
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Physics Term
'Buoyant' is used in physics to describe why objects float, relating to buoyancy force. The science project explained how the boat's design made it buoyant.
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Weight Perception
Something that's 'buoyant' often seems light or weightless. Her inflatable raft was surprisingly buoyant on the lake.