Buoyant

Buoyant is an adjective with two common uses. In physical terms, it denotes the ability of an object to float or rise when submerged in a surrounding fluid. It is also used metaphorically to describe a cheerful, optimistic, or resilient mood or attitude.

Physically, the buoyant force equals the weight of the displaced fluid (Archimedes’ principle). The net force is this buoyant force minus the object's weight. Objects with density lower than the surrounding fluid exhibit positive buoyancy and rise; those with higher density exhibit negative buoyancy and sink; equal densities produce neutral buoyancy, where the object remains at a constant depth.

Many everyday systems exploit buoyancy. Ships and submarines regulate buoyancy with ballast to control depth; hot air and gas balloons rise because the lighter-than-air gas or heated air reduces overall density. In biology, fish and other organisms adjust buoyancy with swim bladders or fats to maintain depth with minimal energy.

In figurative use, buoyant describes an economy or market that is lively and strong, or a person described as buoyant has a cheerful disposition.