I'm trying to be more specific. I described the wrist behavior during last moment (pronation phase) of the kick serve. Yes, I copied the part of my article to save my time. What particular question do you have about my text?
I can answer on your post step by step only, because there too much bits and pieces to discuss. This is about kick serve. We are trying to use Whip Effect to increase the racquet velocity. We want to use our arm like speed multiplier. But, our main concern is ball velocity. In case of the kick serve, the wrist cannot contribute anything to the ball velocity, because it is in stable position (except ulnar deviation). Ulnar deviation produces just spin. The main contributor to the ball velocity would be pronation. But, pronation mostly generated by shoulder joint (handle). Angular speed of the pronation of the upper arm is equal to the angular speed of the wrist. It means efficiency of the Whip Effect =0. There is no Whip Effect at all.
Give me some prove please. I don't want speculation.
Now, you are going to include trunk motion in our discussion. You are also talking about legs and so on. In this case you should describe Kinetic Chain. It looks you have to define new handle (trunk, or legs, or so on) of our passive whip model.
The wrist ulnar deviation does. I stated it many times.
I discribed this motion a little bit in my first post on this website. See http://tt.tennis-warehouse.com/showthread.php?t=251543
I’m sorry. This all staff is very complicated for me. I’m just trying to simplify the matter as much as possible. This is my simple question. Suppose I have two strait pieces of wood, and I connected them end by end, but allow them to rotate with 360 degrees range without friction. There is no gravity. The angle between them is 90 degrees. I move them along the straight line with speed V. There are two linear momentums: M1xV and M2xV. I stop the first one. How many percents of the first stick energy will be transferred to the second one?
The wrist ulnar deviation can be much faster motion then elbow extension. That’s why, it should be used as main contributor (not elbow)to the spin.
According to my calculation, the pronation can generate angular speed around ΩH=6000°/sec. Legs (knees bend, jump, or whatever), shoulders seesaw movement, trunk rotation, and fast elbow joint with forearm, all together produce just ΩV=600°/sec. It would be much more useful to discuss first the arm motion, because it can be the main contributor to the any tennis stroke.
I believe, it could be completely different result. First I should think about the expression “I stop the first stick". What way I can do it? Imagine, it hits tennis net post. This action produces some damage to the post and we lose some stick’s kinetic energy. The stick also gets some damage, again some lost of energy. Then post makes stick to bounce back. I want to prevent this from happening. By using my hand I press the stick back to the post. The stick hits my hand and also creates some damage to it. I push stick back to the post and so on. All this process is harmful for all participants and energy consuming. I believe the stick can lose all its kinetic energy during this struggle. I assume, the joint between sticks allows the second one rotates in the plane perpendicular to the first stick. One end of the second stick abruptly stopped. There also would be damaging and energy consuming fight between joint and second stick, but not so dramatic. Because, the second stick has option, to convert its linear energy to angular one. This energy would be equal m2xVxV/2 minus some lost of energy, because of the struggle with joint and first stick. The second stick without friction will rotate forever. So far, I do not see any energy transfer from first stick to the second one, but everybody got hurt. Right now I understand stuff like tennis elbow, wrist and shoulder injuries. That why Federer never straightens his elbow. He is really smart guy.
I agree, except, you have to keep boll near 3 o’clock. If it’s near 9 o’clock, the racquet runs away from the ball. But, in case of the flat serve you can completely lose the ball direction control. The pros never use this idea for flat serve. In case of the slice serve pros usually keep ball near 9 o’clock and during impact they just brush it in 3 o’clock direction. They are using the same approach to any spin serve. To create good efficiency of the pronation (it is = sin(beta)) you should provide proper value of the angle beta. The angle beta is angle between long axis of the racket and forearm. I describe this matter in details in my first post on this site. I already recommended you to read this post. You also can watch the videos: http://www.vimeo.com/10566621 [URL]http://www.youtube.com/watch?v=1t6bL...eature=related[/URL][/
Usually the racket’s weight is much more than the ball’s weight. That’s why there is no problem. The racket speed practically is not affected by the ball.
I agree about green patch. The linear speed of the any racquet patch is |V|= Ω x R, where: Ω - angular racquet speed, R - rotation radius. R is the shortest distance between the long axis of the racquet and particular patch. In case of the green patch R=0, hence |V|=0.
I’m absolutely agreed with you. But, when I analyze frame by frame 300 fps video, I do not see any racquet deceleration. Hence, something should compensate the inevitable lose of the kinetic energy. What it can be? I think, arm muscles (including wrist muscles) provide this compensation. This is one more argument that wrist cannot be passive. But, I’m not 100% sure about it.
I agree, that racquet should never rotate along its longitudinal axis, because in this case radius of the rotation could be zero (if ball is on green patch it is exactly zero) and pronation component of the racquet speed will be zero. But, it is extreme that during forearm pronation on a serve the racquet should be close to perpendicular (angle beta=90) to the axis of the forearm. The best servers usually keep angle beta around 30-45. If the angle beta = 90, pronation efficiency =100%.
Which time moment are talking about?
Let me analyze one more very simple example. I’m driving car. The car speed is V. My speed is also V. Then the car collides with mountain. Will the car transfer any its kinetic energy to me? If it did I would be definitely killed, even save belt doesn’t save me. Thanks god, the car just cannot do it. My speed still be equal V. I believe the same result would be in case any tennis shot. Our body just cannot transfer kinetic energy of the trunk, knees, shoulder (whatever) to the wrist. Otherwise, our wrist would be completely destroyed. What do you think about this matter?
Let’s analyze the example. The ball (during impact) stays on the racquet bed around 2 msec. Assume, it leave racquet with speed equal 125 mph (200 km/h). The mass of the ball is 57 grams. I calculated kinetic energy of the ball and divided it by time = 2 msec. It would be the power of the racquet produced during impact and it is 60 hp. The result is astonishing! Assume the racquet lost 20% of its the kinetic energy. To compensate it, the arm muscles (or just wrist muscles???) should generate power = 12hp. I believe it is completely impossible. In this case, it doesn’t matter the wrist is active or not. Maybe my analyses of the 300 fps were wrong? To make it accurate I need at list 1000 fps videos. But, I cannot find them.
If forearm (by using elbow extension) rotates in plane parallel to the racquet string plane, it can produce brushing motion only, which mostly can create just spin. You stated it already many times.
