Centripetal Force
Centripetal Force is the inward pull that keeps something moving in a curve.
Think of it this way
When you swing a ball on a string in a circle, the string pulls the ball inward toward your hand. That inward pull is centripetal force. Without it, the ball would fly off in a straight line. The tighter you pull the string, the sharper the curve the ball follows.
Explaining centripetal force by grade level
When a go-kart turns a corner, it wants to keep going straight. Something has to pull it toward the inside of the turn. The tires grip the road and pull the kart inward. Without that grip, the kart would slide off the track.