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Old 01-09-2011, 03:31 PM   #124
toly
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Default Why pros spread their fingers (Roddick pistol grip)?

Quote:
Originally Posted by charliefedererer View Post
But it was Systemic Anomaly that pointed out that the term "lever" is technically correct if you consider the action at the elbow as a third class lever, with the force between the fulcrum [at the elbow] and the distal load [the racquet].
So perhaps the use of the term "leverage" actually does explain the principle force/speed generated in the arm during the serve. The last bit of pronation at the end merely redirects the vector of the force.
The arm pronation rotates the racquet in horizontal plane; hence the gravity is not important. In this case we cannot use directly first-class lever etc model. But, to simplify the matter, let assume the racquet’s inertia behave like gravity force (load). Figure 1 and figure 2 demonstrate the hand’s functions, while pronation beta angle is 90.

Figure 1
The part of the hand around index finger creates force F1. The pinky could be some kind of fulcrum. It would be like third-class lever. The force F1 generates torque T = F1*D, where D is the size of hand , see fig. 1. To increase D, and thus torque, a lot of tennis players spread their fingers.


Moreover, the hand around pinky is also able to exert force F2, see figure 2.

Figure 2
The index finger would be fulcrum. The hand works like first-class lever and creates torque T2 = F2*D. Torques T1 and T2 would rotate the racquet in horizontal plane.
If pronation beta angle equal zero, the hand can treat the racquet handle as well as the handle of the screwdriver only. The racquet handle diameter (d) is usually much less than the size of the hand with spread fingers (D). And hence, the hand produces much less torque than in case as beta = 90.
if the beta angle is any value between 0 and 90, then the torque can be calculated according to formula T =F((D-d)sin(β) +d).
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Last edited by toly : 02-29-2012 at 08:16 AM.
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