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09-05-2012, 11:47 PM   #175
stoneage
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Join Date: Apr 2010
Location: Stockholm, Sweden
Posts: 243

Quote:
 Originally Posted by jmnk I do not think there's anything particularly theoretically special about claiming that a racket with MgR/I = 21 is 'the best'. If I follow travlerajm posts properly he just observed statistical correlation between player's rank and player's rackets MgR/I value, and from that he therefore deducted that 21 is the optimal value. Now, it is interesting but in my opinion unfortunately a bit far fetched. Per his own data the accuracy of MgR/I needs to be calculated with 0.1 precision. that means to back up his claims with empirical data (that is player's rackets specs) that data must be pretty darn accurate. However per his own admission he just estimated the mass and swing weight of the player's rackets based on available specs for mass and balance for unstrung rackets (see http://tt.tennis-warehouse.com/showthread.php?t=387620). Is that possible - well, estimation is, but you can't really use the result of the approximation in cases where the very exact number is needed. Or in other words - the formula used to calculate swing weight based on mass and balance of the racket, and assumption about racket's weight distribution, developed by Cross (I think), while indeed gives pretty decent result as far as swingweight is concerned, is by no means an absolute theoretical truth in the sense for example the parallel axim theorem is. Now if you add to this the fact that you are supposed to adjust the value if you wear a sweatband - than I think we are leaving the realm of physics....
I most wholeheartedly agree and it should never have tried to enter the realm of physics

It is a pity since there are obviously a lot of data behind it (even if you doubt the accuracy of some of it) and there are people who are happy with the result when using it. So can you use it as some kind of rule of thumb if you leave all that unfounded talk about double pendulum and zero moment on the wrist behind? Maybe.

Start by dividing by g, since it is only there to confuse things. You then get:
MR/I= 2.14

Now invert it to get a more practical unit, you then get:
I/MR = 0.467 m or 46.7 cm

Call it a normalized balance (NB) or something like that and say that a rule of thumb is that NB should be around 47 cm, without claiming any physical background. It would be like a BMI for a racquet. BMI doesn't claim any deeper background, just based on observations it says that a healthy normal person has a BMI between 20 and 25.

But as a rule of thumb you should also open up for other values. Why should recreational player have the same value as a pro?

Last edited by stoneage; 09-06-2012 at 12:00 AM.