centripetal force

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The component of force acting on a body in curvilinear motion that is directed toward the center of curvature or axis of rotation. Centripetal force is necessary for an object to move with circular motion.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun physics The force on a rotating or orbiting body in the direction of the centre of rotation.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the inward force on a body moving in a curved path around another body