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Old 10-04-2012, 05:09 PM   #232
bhupaes
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Join Date: Aug 2007
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Quote:
Originally Posted by toly View Post
The Oscar Wegner in video http://www.youtube.com/watch?v=MxUPDHegz98 around 2.50 demonstrates across motion and side spin. In our example Nadal create mostly topspin, see original video. You also can ask JY about sidespin in this particular Nadal FH video.
Well, he's talking about Federer - and I would expect Federer to produce more sidespin. Again, remember, you have shown us one example of Nadal. I have seen him hit vicious sidespin on many occasions. But I still maintain the sidespin is a side effect of the technique used, and may or may not always happen.

Quote:
Wegner also said, around 6.30, that Federer slowly goes to the ball then all acceleration occurs sideway. IMO there is no correlation among his explanations and videos of Federer and Nadal FH.
I think you've misunderstood. Oscar doesn't say all acceleration is sideways. He only points out that there is a strong sideways pull near the point of contact. Also, "slowly" is relative - all it means is that in the initial phase, RHS is considerably slower than the contact phase, as far as I am concerned.

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Tell me please, in what frame exactly Nadal begins sideway acceleration.
In the picture I included in my post, assuming each overlay is a frame, probably around the 18th frame.

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When Nadal rotates the arm around shoulder, he creates centrifugal force which has normal component to the racquet string plane. This force normal component (motion dependent torque) automatically rotates the racquet in clockwise direction, see Rod Cross article http://www.racquetsportsindustry.com...the_serve.html.
This normal component is function of angle (ϕ) between arm and racquet. If ϕ=0, this component is zero. This normal component is also function of arm angular acceleration. The more we accelerate angular rotation the less is motion dependent torque.
Okay...

Quote:
On other hand, Nadal applies extremely hard arm pronation/ISR. This is also angular rotation, which also creates its own centrifugal force and motion dependent torque. Rod Cross completely ignored this fact.

Moreover, this motion dependent torque pushes the hand to rotate the racquet in clockwise direction, opposite to the torque created by arm rotation. So, there is no automatic motion dependent whip effect. I believe, Nadal creates very fast wrist/hand swing, by using extremely actively hand’s (or whatever) muscles.
I think you still remember the physics, you can get it.
Ah, there you go again, toly! We've hit on our fundamental area of disagreement one more time... passive vs. active wrist! Unfortunately, neither you nor I can prove our points from photographs!

Let me also point out that in the video of Oscar you have posted, he shows a combination of upper arm rotation and biceps action when he is pulling the racquet in. I think this is natural for most people, and we have an extreme example in Nadal.

Last edited by bhupaes : 10-04-2012 at 05:16 PM. Reason: Changed 15 to 18.
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