Uniform Circular Motion

Objects moving in circular motion must be accelerating, since acceleration includes both speed and direction. The objects are accelerated by real forces that add up to a center-directed net force called the centripetal force. Any object moving in a circular path at constant speed is subject to a net force equal to the mass times the velocity squared divided by the radius of the circle, and is accelerating at a rate equal to the velocity squared divided by the radius.

To gain more insight into the relationship between the tension and the gravitational force in vertical circles, explore this simulation from the Department of Physics at the University of Toronto. 

For more information on circular motion view the video clip Tangential Speed and Centripetal Force from Discovery Education™ streaming.