Here's why:
* Centripetal means "center-seeking."
* Acceleration is the rate of change of velocity.
* Velocity has both speed and direction.
When an object moves in a circle, its direction is constantly changing, even if its speed is constant. This change in direction means the object's velocity is changing, which requires acceleration. That acceleration is always pointed towards the center of the circle, hence the term "centripetal."
Think of a ball on a string being swung in a circle. The string is constantly pulling the ball inwards, causing it to accelerate towards the center of the circle.
