11.2

1. 11.2 Floating and Sinking

2. Buoyancy • When you pick up an object underwater it seems much lighter due to the upward force that water and other fluids exert known as the buoyant force • The buoyant force acts in the direction opposite to the force of gravity, so it makes an object feel lighter • Since the pressure of a fluid increases with depth, the upward pressure on the bottom of the object is greater that the downward pressure on the top, resulting in the buoyant force • The weight of a submerged object is a downward force • An object sinks if its weight is greater than the buoyant force • If the weight of the submerged object is equal to the buoyant force, the object floats

4. Archimedes’ Principle • Submerged objects displace, or take the place of, a volume of fluid equal to its own volume • Archimedes, a Greek mathematician discovered a connection between the weight of a fluid displaced by an object and the buoyant force acting on it • Archimedes’ Principle states that the buoyant force acting on a submerged object is equal to the weight of the fluid the object displaces

5. Density • The density of a substance is its mass per unit volume • By comparing densities, you can predict whether an object will float or sink in a fluid • An object that is more dense than the fluid in which it is immersed will sink • An object that is less dense than the fluid in which it is immersed will float • If the density of the object is equal to the fluid, it will float at a constant depth

7. Changing Densities • Submarines are a prime example of changing densities • When a submarine dives, it takes on water increasing density and making its weight greater than the buoyant force • When a submarine surfaces, it releases water decreasing the density and making it weight less than the buoyant force