Middle School Physical Science: Fluid Forces - Buoyancy of Fluids — Flashcards

Buoyancy, or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid.

Archimedes' Law    
Did you ever notice that when you get into a bathtub of water the level of the water rises? More than 2200 years ago, a Greek mathematician named Archimedes noticed the same thing. He observed that a body and the water in a tub can't occupy the same space at the same time. As a result, some of the water is displaced, or moved out of the way.    
How much water is displaced? Archimedes determined that the volume of displaced water equals the volume of the submerged object. So more water is displaced by a bigger body than a smaller one.    
Archimedes discovered that the buoyant force acting on an object equals the weight of the fluid displaced by the object. This is known as Archimedes' law. It explains why some objects float in fluids even though they are very heavy.

For example, an extremely heavy ship is able to stay afloat because the design of its hull causes it to displace a lot of water. The weight of the displaced water is greater than the weight of the ship, so the buoyant force is greater than the force of gravity acting on the ship. As a result, the ship floats.