Centrifugal
inertia of an object moving in circular motion, causing it to move away from the center. It is not really a force.
Velocity is a vector quantity (it adds according to the Parallelogram law). A velocity vector will have a magnitude component (speed) and an orientation component (direction). If a body has constant velocity, it is traveling at a constant speed in a constant direction (i.e. in a straight line). If a body is traveling at a constant speed in a circle, its direction and thus its velocity is constantly changing. A time rated change in a velocity vector is acceleration, even though the speed component of the velocity vector remains constant.
We know from Newton's first law of motion that a body will maintain a constant velocity unless a net force (the sum of all the forces acting) acts upon it. Thus when a body travels in a circle a net force must be applied to stop it from traveling in a straight line. This force is the centripetal force, the only action force necessary for a circular motion. It is accompanied by a reaction force - on the object providing the centripetal force - by Newton's third law of motion.
What is sometimes interpreted as a "centrifugal force" is its inertia, which would cause it to move in a straight line, tangent to the circle, if not for the centripetal force.
Physics teachers are keen to teach that the real force is centripetal force and that centrifugal force is the reactionary force which balances it. Conversion of angular momentum into linear momentum is used in a number of ways, the most obvious is perhaps a sling.
See also: Coriolis force, centrifugation, trebuchet
