Circular Motion in Physics

Circular motion is a very important topic in physics. Let us consider an object in uniform circular motion about the origin. The speed of the object is constant, is it accelerating? At first glance it seems like the answer is no as the speed is not changing. However acceleration is defined as change in velocity, not change in speed. Recall that velocity is a vector quantity, vectors have a magnitude and a direction. So even thought the speed is constant, the direction of the vector is in constant flux, and therefor the object is undergoing uniform acceleration. Now in what direction is the acceleration? It's always pointed to the center of the circle. As an example imagine a rock tied to the end of a string which you swing in a circle above your head. What happens if you cut the string? It would fly off in a straight line, so you can see it requires a force to keep an object in circular motion. In this case it's the tension force of the string holding the rock on the circular path. In the case of the moon orbiting the Earth it's the force of gravity holding the moon in a circular path. So the main take away is that an object in uniform circular motion requires a force to hold it in the circle and is accelerating towards the center of the circle at all times.