What Causes Centripetal Acceleration and Centripetal Force?

Direct Answer

Centripetal acceleration occurs because an object's velocity continuously changes direction as it moves in a circle. A resultant centripetal force directed toward the centre causes this acceleration; it is not an additional type of force.

This content is part of IB Physics A.2 Forces and momentum for both SL and HL.

The Mechanism

Velocity is a vector, so it changes whenever its magnitude or direction changes. During uniform circular motion, speed remains constant, but the velocity direction changes continuously; therefore, the object accelerates toward the centre of the circle.

Over a short time interval, subtracting the initial velocity vector from the final velocity vector gives a change in velocity, $\Delta v$, directed approximately inward. As the interval becomes smaller, this direction approaches the radius toward the centre. Since acceleration is $\Delta v/\Delta t$, the acceleration is inward even though the speed is unchanged.

The acceleration magnitude is