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Old 07-06-2011, 04:51 AM   #4
kaiser's Avatar
Join Date: Feb 2010
Location: Holland - Belgium
Posts: 695

Originally Posted by travlerajm View Post
Reserved for analysis of data:

The MgR/I value gives a measure of the racquet's natural swing frequency as it pivots about the wrist axis on a forehand.

A groundstroke can be simply modeled as a double pendulum, with the upper pendulum swinging from the shoulder, and the lower pendulum swinging from the wrist. The speed of the upper pendulum is mostly related to the length of the player's arm, while the speed of the lower pendulum is largely a function of the racquet's weight's distribution. The frequency of a pendulum is proportional to sqrt(MgR/I), where M is the mass of the pendulum, g is the acceleration of gravity, R is the distance from the pivot point to the center of mass, and I is the moment of inertia about the pivot point. Thus, a racquet's MgR/I value gives a measure of it's natural swing frequency. It is not necessary to take the square root, because only relative values are needed.
Trav, there is something about yopur MgR/I formula I've been wondering about for some time now. What pendulum action around the wrist are you referring to? When you look at slomo movies of e.g. the Federer forehand, you can clearly see that most of the accelleration towards the ball occurs in the horizontal plane (for an example, see So how does g, the accelleration due to gravity, which only occurs in the vertical plane, affect the pendulum around the wrist? Wouldn't the horizontal accelleration component of the racket arm, as generated by the player, be more important here?

Also, when you look at the pendulum action of the wrist, the wrist remains usually completely laid back up untill the point of contact with the ball. That is, the pendulum action around the wrist joint typically occurs after the ball is hit, during follow-through. Then how can this pendulum motion so crucially affect the stroke and, indeed, a player's ranking if it takes place after ball contact?

I'm looking forward to your explantion.

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