Objects in fluids have more pressure on bottom surface than on top surface {buoyancy}|, because bottom surface is deeper in fluid. The greater force on bottom pushes object up. Buoyancy equals difference between object-bottom pressure and object-top pressure. Buoyant force is in opposite direction from gravity. Objects that sink have more force than fluid weight pushed up. Objects that sink are denser than fluid.
If objects float in fluid, fluid weight pushed up around object equals upward buoyant force on object {Archimedes principle, buoyancy}|.
Object in fluid pushes fluid out {displacement, fluid}|. Fluid tries to return to original position by gravity. Displaced fluid and object both want to occupy same place. Equilibrium happens when both forces push down equally.
Objects can sink until buoyant force balances gravity {floating}|. Displaced fluid and object both want to occupy same place, so object is at equilibrium when fluid force pushing down equals object force pushing down. Object that floats is less dense, including air spaces, than fluid. Submarines, fish, boats, balloons, and ice cubes demonstrate buoyancy. If floating-object mass center is not along buoyant-force line, object rotates around mass center.
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Date Modified: 2022.0225