View Single Post
Old 07-12-2011, 01:58 PM   #49
Hall Of Fame
Join Date: Dec 2006
Location: Bedford,Massachusetts,US
Posts: 2,014
Default C1 and C2 both equal zero

Originally Posted by travlerajm View Post
The double-pendulum stroke represented in Fig. 4 of the Cross paper is a reasonable simulation for a golf swing or a tennis serve, but not for a forehand.

For a golf swing (or a tennis serve), the ball is stationary (or almost stationary). This means that small errors in timing will not lead to large errors in direction, as they would if the stroke modeled in Fig 4 was used for a forehand.

The stroke of Fig 4 shows that maximum angular velocity of the clubhead is reached right at impact. This is what you want to achieve when hitting a golf ball, because increased angular velocity leads to more power.

On a tennis serve, the same goal applies - maximum racquethead speed is the ideal. So the stroke of Fig is a good model.

But for a forehand, whipping the racquet toward the ball with maximum angular velocity is not a good way to hit the ball. If you are a fraction of a second late with your timing, the incoming ball will travel further before making contact with the racquet. And when it does, the racquetface will have a much different angle (because it is rotating at maximum angular velocity), causing a big error in shot direction and the ball to spray off to your right (if you are righthanded).

I would be interested to see if Cross can set the couples C1 and C2 in his model both to zero (or have C1 increase after the bottom of the swing), and then find values for the weights and lengths of the arm and racquet that permit the hand and racquet to move at the same forward speed through the impact zone.

1.His paper can be transferred from his Web site if you do NOT have it

2.He his an appendex with equations for "both pendula"
I have to see what will happen with C1 and C2 both set to zero
I have a paper copy on me.
3.I disagree with your sentence starting with "But for a forehand"-
there are some experimental data disagreeing with you.
See references in the paper,PROBABLY one of them by Brian Gordon.
He maybe discussing a related issue,but I am NOT sure.
I will do some checking and I will correct my post if necessary
Please see
post #31
It refers to FOREHAND,I believe.
You may want to check with John Yandell

Last edited by julian : 07-12-2011 at 02:20 PM.
julian is online now   Reply With Quote