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01-30-2013, 03:44 PM   #47
sureshs
Bionic Poster

Join Date: Oct 2005
Posts: 34,075

Quote:
 Originally Posted by TheCheese Just because you pull up and across, does not mean there is no forward motion on the swing, Frisbee. What the pulling up and across does is let you impart a ton of topspin AS you drive the ball. It gives much more margin for error and control. Just go out and try it yourself, everyone. It clearly is the way to play.
Of course. That is what everyone does. It is the finer details which are exciting.

When you pull something up and across, where does it go? Take your cell phone right now and pull it up and across as you toss it. What happened? It went up and across and crashed against the wall and shattered.

Does the tennis ball go up and across like that?

No.

That is because most of the energy is in the forward direction with the up and across component coming from forces below the center of mass, and friction with the strings, which create the spin.

One of them is like flicking a vertical wheel on the lower side with an upwards and forwards force. As long as the line of force does not pass through the center of mass (axle) but above it, the wheel will rotate. Another way is to grip the wheel and turn it. These two are analogous to the strike on the ball followed by friction during the dwell time, and both require the across and up component.

If the direction of the force (and hence the swing just prior to it) was merely normal to the ball, it would just go straight. If the across and up direction passed through the center of mass, the ball would also be launched across and up. So it is a combination of the force in the forward direction which also acts up and across in a glancing way, which makes the combination of pace and spin possible.