In uniform circular motion, a particle moves in a circle at constant speed. However, the acceleration is constantly changing. This is because acceleration is a change in velocity, the velocity vector is changing direction. The acceleration vector is always perpindicular to the path and always points toward the center of te circle. This is centripetal acceleration, and its magnitude is defined by the equation below. r represents the radius of the circle. The subscript on the acceleration symbol means that the acceleration is centripetal.

a_c = v²/r