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01-07-2013, 02:33 AM   #88
stoneage
Rookie

Join Date: Apr 2010
Location: Stockholm, Sweden
Posts: 243

Quote:
 Originally Posted by Technatic The formulas for the SW are: Balance point: Bp = W head * L/(W head + W throat)*10^3 Swingweight: SW = Tot Weight * (Bp – Oset)^2 + Tot Weight *( 3*1,5^2*L^2)/12000
You can't calculate swing weight/moment of inertia from weight and balance (as JMNK already pointed out). The formula you give might be used to approximate the swing weight for some racquets. But it assumes a certain weight distribution in the racquet so you can never know whether it is correct or not. And in contrast to the real swing weight it doesn't add any new information about the mechanical properties of the racquet.

To give an example why this doesn't work lets consider three racquets, all 70 cm long and with a mass of 250 gram evenly distributed. Then:
to A: Add 50 g evenly distributed
to B: Add 50 g to the midpoint
to C: Add 25 g each to the top and bottom

You end up with three racquets that have that same mass (300 g) and the same balance point. So if you try to calculate the swing weight from these two values you will end up with the same swing weight, independent of which formula you use. With your method all three will be identical.

If you instead calculate the actual swing weight for these racquets you will get:
A: 310 kg cm^2
B: 290 kg cm^2
C: 350 kg cm^2

Which clearly is a significant difference.

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Last edited by stoneage; 01-07-2013 at 06:09 AM.