The duration the ball remains in contact with the rubber on a table tennis racket – also called dwell time – determines how much momentum and energy is transferred to the ball from the force exerted by the racket on the ball. If the racket accelerates simultaneously as the ball accelerates, the duration the ball remains in contact with the rubber is larger. The timing of racket head acceleration is very important as it should closely match the time the ball stops moving away from the net and start moving toward the net again. This means the stroke should transition from slow to fast (accelerate or snap) on impact with the ball to transfer a larger amount of energy and momentum to the ball.