A centrifuge is a machine designed to apply a sustained centrifugal force to an object or experimental sample. These devices range from bucket on a rope swung around in circles to large metal devices with motors that spin on a shaft rotating samples in a lab. They have a number of uses, ranging from subjecting astronauts to high G forces to separating molecules in chemical samples of different masses. Due to the fact that Earth's gravitational force and centrifugal force have the same properties, the for exerted on an object in the centrifuge is measured in how many times the pull of normal gravity it is or "Gs".

Isaac Newton's first law of motion states that moving object continues in a straight line unless a force is exerted to deflect it. Objects moved in a circular path with the reaction against the deflecting force is said to have centrifugal force. The amount of force exerted by a centrifuge on an object can be give with the equation

F = 0.00001117n2 × R × M

with force F expressed in grams, n being the rotational speed in RPMs, R being the radius in centimeters, and M being the object's mass in grams. High speed centrifuges are limited by the strength of the materials used to make them because as the speed increases, the diameter must decrease. Centrifugal force is proportional to the square of the speed and because of this strong gravitational fields can be formed in very small centrifuges.

One of the more notable centrifuge derived inventions is the analytical ultracentrifuge, a device invented by Theodor Svedberg in 1925. It is optimized for spinning at very high speeds and can produce G forces up to 1,000,000 Gs and is used for observing macromolecules. When done correctly, you can tell the shape, stoichiometry, approximate molecular weight, and the conformational changes in macromolecules.

Sources:
http://www.wikipedia.org/
http://go.grolier.com/uni.html