In
science,
buoyancy ( or ; also known as
upthrust) is an upward force exerted by a fluid that opposes the
weight of an immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the pressure at the bottom of a column of fluid is greater than at the top of the column. Similarly, the pressure at the bottom of an object submerged in a fluid is greater than at the top of the object. This pressure difference results in a net upwards force on the object. The magnitude of that force exerted is proportional to that pressure difference, and (as explained by
Archimedes' principle) is equivalent to the weight of the fluid that would otherwise occupy the volume of the object, i.e. the
displaced fluid.