11.2Floating and Sinking

BuoyancyWhen 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

Archimedes’ PrincipleSubmerged objects displace, or take the place of, a

volume of fluid equal to its own volumeArchimedes, 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

DensityThe density of a substance is its mass per unit

volumeBy comparing densities, you can predict whether

an object will float or sink in a fluidAn object that is more dense than the fluid in

which it is immersed will sinkAn object that is less dense than the fluid in which

it is immersed will floatIf the density of the object is equal to the fluid, it

will float at a constant depth

http://www.google.com/url?sa=i&rct=j&q=density&source=images&cd=&cad=rja&docid=ZPX2x34JCDvlAM&tbnid=2eSlI1PXYXhPaM:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.stevespanglerscience.com%2Flab%2Fexperiments%2Fdensity-tower-magic-with-science&ei=HEX5UrrwHuLy0gHz14HIAQ&bvm=bv.60983673,d.eW0&psig=AFQjCNEDVYfR8-ZUYsdMkY7xyhvCDkrbbQ&ust=1392154258254976

Changing DensitiesSubmarines are a prime example of changing

densitiesWhen 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