It is hard to define “power” of racquet. According to [4] power could be defined as

1. racquet bounce (high coefficient of restitution)
2. high swing weight (high angular momentum)
3. low work (racquet which gives the greatest ball speed with a given player effort)

The easiest way to understand power is the coefficient of restitution (COR). The maximum power occurs when the COR is the greatest.

 

The coefficient of restitution is the ratio of the differences in velocities before and after the collision. COR is defined as difference in the velocities of the two colliding objects after the collision, divided by the difference in their velocities before the collision.

COR = coefficient of restitution

= linear velocity of the racquet mass center before impact

= linear velocity of the ball before impact (will be negative according to our convention that away from the player is positive)

= linear velocity of the racquet mass center after impact

= linear velocity of the ball after impact

From the coefficient of restitution formula, it follows that

To find the coefficient of restitution in the case of a falling object bouncing off the floor, or off a racquet on the floor, we can use the following formula:

where: is rebound height

is initial height

According to [5], the highest coefficient of restitution (power) is near the tip of the head.

COR

COR (center of mass): .74162

COR (near the throat): .63246

COR (tip of the head): .7746

Sweet spot is the position of optimum vibration. When the ball hits the sweet spot player does not feel the impact of the ball, because a minimal kick or jar is transmitted to the player's hand. The strings absorb the vibration that increases stability of the racquet in the player's hand and player has more control over the racquet.

“The sweet spot is determinative of the force from impact: the higher the sweet spot, the lower the Impact Force acting at the racquet's mass center, and the more positive the Impulse Reaction” [5]