Momentum Transfer

At impact, the clubhead slams a stationary ball in a collision lasting about half a millisecond. In that instant, the ball compresses against the face and stores elastic energy like a spring, then snaps back to launch.

The coefficient of restitution describes how elastic the collision is - how much speed survives rather than disappearing into heat, sound, and deformation. Golf's rules do not let equipment become arbitrarily springy: driver faces are limited through spring-effect tests such as COR or characteristic time, while golf balls are controlled by separate initial-velocity and distance standards.

Clubhead mass matters because momentum equals mass times velocity. A heavier head at the same speed transfers more momentum to the ball. But heavier heads are harder to swing fast, so the best design balances mass and speed for maximum energy transfer at impact.