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09-04-2012, 08:18 PM   #171
corners
Legend

Join Date: Jul 2008
Posts: 5,440

The following were questions posed to Travlerajm, but I'd like to add a bit of response as well.

Quote:
 Originally Posted by stoneage Thanks for the clarification! I have had two problems with MgR/I: 1. I have yet to hear an explanation why this parameter is relevant to the mechanical behavior of the racquet in tennis. MgR/I describes how the racquet swings freely in a gravitational field, i.e. like a pendulum. MgR/I=21 means that frequency of a racquet swinging from the but is 0.73 Hz. But unless you are building a cuckoo clock of the racquet I have difficulties to see the relevance. Gravity is the least of forces involved in a tennis swing. But if you have some explanation that could shed some light on this I would be most interested (no irony intended).
Rod Cross has been modeling tennis strokes, including the serve, as double pendulums for several years, with two papers appearing in the past twelve months.

Quote:
 2. There are an infinite number of racquet configurations that fulfill MgR/I=21 most of them very strange and unplayable. So if you use only that to find an optimal racquet you could easily go wrong.
This isn't the case. Many racquets on the market are reasonably close to 21.0, especially traditional players' frames like the Pro Staff 6.0 and the Prestiges. I support your skepticism but I think you're misinterpreting this notion of MgR/I and its use. It's not meant as a stand-alone, be all/end all.

I suspect that if you try some on-court experiments, like the following two, you'll find some value in the approach:

Experiment #1: Alternate between two frames with very different MgR/I values but with very similar swingweights and static weights. The two frames will differ only in balance point.

For example: Racquet A at 335 grams / 31.5 cm balance / 320 swingweight (MgR/I = 20.8 ) and Racquet B at 335 grams / 33.0 cm balance / 320 swingweight (MgRI = 21.37).

Experiment #2: Alternate between two frames with the same MgR/I values (how about 21.0?) but with very different static weight, balance and swingweights, such as:

Racquet A at 350 grams / 31.5 cm balance / 330 swingweight (MgRI = 21.0), and Racquet B at 335 grams / 32.0 cm balance /320 swingweight (MgRI = 21.0). Or better yet, your preferred specs and another very different configuration with the same MgR/I ratio as your preferred specs.

If the ratio doesn't make some sense to you after these experiments then we can confidently add your report to the "MgR/I is rubbish." pile of anecdotes.

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