Up until now, our Newton’s second law problems have focused on objects that moved along a line. If the velocity and acceleration vectors pointed in the same direction, the object would speed up.  If they pointed in opposite directions, the object would slow down.  If the acceleration was zero, it motion wouldn’t change.  But what our object hasn’t done before now is turn off of the line it was initially traveling along.

Allowing our object to turn gives us a new type of motion, one that is no longer just linear. To start with, we will consider the simplest type of motion where an object turns, uniform circular motion.  In uniform circular motion, an object moves along a circle at a constant speed because the velocity and acceleration vectors are always perpendicular to each other.  The acceleration always points towards the center of the circle, making it a centripetal acceleration.  As we will see, we can relate the centripetal acceleration to the centripetal force which causes the object to move along a circular path.