Why does a tennis racket have a springy web of strings?

A tennis ball seems to strike a flat racket face, but the strings briefly dip into a shallow pocket. Both the ball and the string bed deform. That momentary change of shape helps determine the speed, direction, and feel of the returning shot.

The strings are stretched under tension before the ball arrives. Impact bends them out of their original plane and stretches them further. They store elastic energy: energy associated with a change of shape. As they recover, they push on the ball and return some of that energy.

The ball also compresses, but it does not return all the energy used to squash it. The relative stiffness of ball and strings affects how the deformation is shared. A softer string bed may allow more movement in the strings and less compression in the ball. That does not guarantee that every softer racket produces a faster shot; the swing and impact location still matter.

Strings can also move sideways during a brushing impact. Friction between ball and strings, along with sideways string movement and recovery, can change the ball’s spin. Rebound and spin are related but different effects. A racket is therefore a temporary energy store and a carefully controlled contact surface, not merely a net that blocks the ball.