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09-07-2012, 06:57 PM   #199
travlerajm
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Join Date: Mar 2006
Posts: 4,394

Quote:
 Originally Posted by stoneage Yes a lot of people like it, then why not be satisfied with that? Put up the specs and say "try this, I have no clue why, but it works". Instead you have decided to ice the cake with a lot of quasi physics. You are repeating time after time that it is based on simple laws of physics, but you have never been able to show it, or even tried. Wrong both from a mechanical and tennis perspective. Gravity acts downwards and is difficult to convert to the forward motion of the racquet when you hold it from the side. And even if you could the contribution would not be that great, 0.5 m drop would add 3 m/s to the swing speed at most. And the high take back is part of a circular swing so when the acceleration starts the position is fairly low Federer Djokovic Another example of the quasi physics I was talking about. When I asked about a proof or background to a similar statement earlier you replied that there was no calculation or measurement but " that you could feel it in you hand". I guess that this is about as well founded. I am trying to decide whether this statement is outrageous or just plain funny. You need a precision that would make NASA envious: The force on the hand in a normal forehand swing parallel to the ground is about 0.00003% higher in Belgium than in Buenos Aires due to difference in gravity. Do you take the position of Venus and Mars into account as well?
For someone who is so interested in equations, I'm not sure why you continue to argue against a concept based on Physics 101:
http://hyperphysics.phy-astr.gsu.edu/hbase/pendp.html

Your arm behaves very much as a physical pendulum. And so does the racquet. And yes, using the assumption that MgR/I = 21.0 to estimate the gravity contribution to the velocity of the hand at the bottom of the swing (from potential energy of the arm), you get about 3m/s. Since a typical high level forehand has forward racquet velocity of about 20m/s, gravity contributes about 15% of the forward racquet velocity of a forehand.

But that is not the point. The point is that, over the first half of the stroke (from top of backswing to the bottom of the swing), if your wrist is relaxed, almost 100% of the racquet's angular acceleration comes from the gravity contribution, which depends on the MgR/I term. So in the absence of any adjustment from the wrist muscles, the angle of the racquetface at the moment you start to apply force to further accelerate the racquet is almost entirely dependent on the MgR/I term.

The point is that tuning the racquet's natural swing frequency to match the natural swing frequency of the arm will significantly improve control. by ensuring that your racquetface naturally stays perpendicular to your target as it passes through the hitting zone.

Also, I point out again that g value can indeed vary by as much as 0.3%, depending on your location on the globe, even for two cities both at sea level. This can make a difference in MgR/I of up to 0.06, enough to throw off your timing if your racquet is perfectly tuned (as I like mine to be). I'm currently building a customized frame identical to my own racquet for a friend I met through TTW who lives in Singapore that tried my frame when he visited in Seattle. The g value in Singapore is only 9.78, so I will need to adjust for that.
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POG OS. 368 SW, 12.54" balance, 21.0 MgR/I.
Problend kevlar 16 / Prestretched SPPP 17, 72/50 lbs.

Last edited by travlerajm; 09-07-2012 at 08:25 PM.