Uniform circular motion can be described as the motion of an object in a
circle at a constant speed. As an object moves in a circle, it is constantly
changing its direction. Because of this direction change, you can be certain
that an object undergoing circular motion is accelerating (even if it is moving
at constant speed). And in accord with Newton's second law of motion, an accelerating
object must be acted upon by an unbalanced force. This unbalanced force is
in the same direction as the direction of the acceleration. For objects in
uniform circular motion, the net force and subsequent acceleration is directed
inwards. It is often said that circular motion requires an inward (or "centripetal")
force.
Without a centripetal force, an object cannot travel in circular motion. In
fact, if the forces are balanced, then an object in motion continues in motion
in a straight line at constant speed
Without
a centripetal force, an object in motion continues along a straightline path.
