"Accelerate evenly through the ball"

[SystemicAnomaly]

Originally Posted by 5263

... Also did you notice that Cross' appears to support some accel even slightly after contact according to his charts and confirmed by Julian if I understood both of them.

Originally Posted by julian

He is referring to the paper of American Journal of Physics-my first link in one of my posts above
Fig 4

http://www.physics.usyd.edu.au/~cros...ennisDPend.pdf

Compare Fig 4 of the link above with Fig 10 of the TWU link below. Why do they differ? Is one of them incorrect? Am I overlooking something here?

http://twu.tennis-warehouse.com/lear...lependulum.php

This graph from the TWU link makes more sense to me than Fig 4 from the 1st link. I would expect a reduction in the speed magnitude of the racquet (head) during contact. Fig 4 does not appear to indicate any consequence of the impact at contact time. The TWU graph seems to confirm what we see in the animation below. Can you guys pls enlighten me on why the other graph appears to contradict these other 2 sources?

http://www.science-animations.com/support-files/tennis.swf
.

[skiracer55]

...this is what matters...

Originally Posted by LeeD

You were the only one.
Everyone knows the finish is just as important as the start, which forces you to complete your stroke each and every time.

[julian]

Originally Posted by SystemicAnomaly

I believe that we let the racket decelerate rather than abruptly stopping it (unless we are volleying). To me, "during contact" would be that 4 ms or so of contact. The racquet head would be slowing down during that time.

I suppose that we tell the student what we feel that they need to hear. Some students might like all the dirty (physics) details while most would probably not. We tell students what is needed to elicit a desired result. Sometimes, as coaches, we even will say things that we know might not be technically correct to elicit a desire action.

g2g, I'll have to look at your other questions later.

A bit related
http://www.youtube.com/watch?v=p913f...ature=youtu.be
1.I may try to start a different thread if necessary
2.I did NOT see a device.racket described in the thread
3.See as well
http://www.sportstechreview.com/2012...tennis-racket/
http://tt.tennis-warehouse.com/showthread.php?t=419169
http://tt.tennis-warehouse.com/showthread.php?t=412968

[5263]

Originally Posted by SystemicAnomaly

Compare Fig 4 of the link above with Fig 10 of the TWU link below. Why do they differ? Is one of them incorrect? Am I overlooking something here?
.

I think the ones that don't show the short continuation of the accel just after contact are not detailed enough. I expect the duration is so short, that it leads
to this whole discussion.

I must say, that to "not intend to accel" thru to penetrate to some extent is a very foreign idea to me. In MA when breaking boards as well and kicking and punting in football, every sport teaches to seek to accel thru the impact a short distance for most powerful result. Often those who don't when breaking boards, not only don't succeed in the board break, but also injure their hands in the effort. I feel pretty sure that accel thru the contact is best to avoid injury and shock in tennis as well.

[julian]

Originally Posted by 5263

I think the ones that don't show the short continuation of the accel just after contact are not detailed enough. I expect the duration is so short, that it leads
to this whole discussion.

I must say, that to "not intend to accel" thru to penetrate to some extent is a very foreign idea to me. In MA when breaking boards as well and kicking and punting in football, every sport teaches to seek to accel thru the impact a short distance for most powerful result. Often those who don't when breaking boards, not only don't succeed in the board break, but also injure their hands in the effort. I feel pretty sure that accel thru the contact is best to avoid injury and shock in tennis as well.

Two very different points:
Please specify whether
"not intend to accel" does refer to a RACKET or HAND or both?
Does it refer to FOREHAND or SERVE or BOTH?

Comment:
Once more Rod Cross says that his graphs are in agreement with the pro data
Additionally data are are the ROTATIONAL part ONLY
Do we doubt pro data?

[5263]

Originally Posted by julian

Two very different points:
Please specify whether
"not intend to accel" does refer to a RACKET or HAND or both?
Does it refer to FOREHAND or SERVE or BOTH?

Comment:
Once more Rod Cross says that his graphs are in agreement with the pro data
Additionally data are are the ROTATIONAL part ONLY
Do we doubt pro data?

Honestly, I care far more about intention and am focused there.
I think Cross does the best job with the data and would use his, but
I still think I see problems with all the data collection. It is very hard
to do well! Collecting data and making best use of it is a huge challenge
presently. I see a lot of poor instruction based on what folks take for facts,
but is really only evidence.

What we intend on our strokes is the key to our performance, and
way more important than what evidence shows is happening.
As coaches, we need to know what intentions get best results IMO.

[julian]

Originally Posted by 5263

Honestly, I care far more about intention and am focused there.
I think Cross does the best job with the data and would use his, but
I still think I see problems with all the data collection. It is very hard
to do well! Collecting data and making best use of it is a huge challenge
presently. I see a lot of poor instruction based on what folks take for facts,
but is really only evidence.

What we intend on our strokes is the key to our performance, and
way more important than what evidence shows is happening.
As coaches, we need to know what intentions get best results IMO.

Did you answer my FIRST question?please see post #45

[5263]

Originally Posted by julian

Did you answer my FIRST question?please see post #45

Hand/handle, as
that is what we manipulate.

[julian]

Originally Posted by 5263

Hand/handle, as
that is what we manipulate.

5263,

so we have a SIGNIFICANT DISAGREEMENT here.
Rod CROSS "suggests" that the HAND SLOWS .5 of sec before the CONTACT
Once more "his pro DATA" are for ROTATIONAL part only ( I use quotations marks to be careful).
As a coach I agree with Rod
I can try to figure out how pro data were collected
Whether we can get videos supporting these pro data is completely different issue

[5263]

Originally Posted by julian

So we have a SIGNIFICANT DISAGREEMENT here.
Rod CROSS "suggests" that the HAND SLOWS .5 of sec before the CONTACT
Once more DATA are for ROTATIONAL part only
As a coach I agree with Rod

And this is why I focus on the players intent.
We can find data that shows lots of bits and pieces.

Maybe the intent to accel the hand only results in less Decel, so
that is fine as well.

[bhupaes]

First and foremost, all this physics stuff should be purged out of one's mind while playing - let's be clear about that!

That said, I make sense out of all of this as follows. If you recall how I defined extension (in the extension discussion a few days ago), I said extension reaches a maximum just before impact. At that point, be it a forehand or serve, the hand can go no further, and reaches a maximal point where it slows down a lot. This sudden slowing down of the hand releases the wrist, and the racquet head accelerates to impact. At some point after impact, the wrist can release no further and starts dragging the hand/forearm, which causes the hand/forearm to pick up speed after impact into the follow through.

Well, what does this imply for coaches... that's a good question! I would say a really relaxed wrist, and a good runway into extension by laying the wrist back so there's enough room to accelerate the racquet head. I know I'm not being precise here, but you get the idea.

Originally Posted by 5263

And this is why I focus on the players intent.
We can find data that shows lots of bits and pieces.

Maybe the intent to accel the hand only results in less Decel, so
that is fine as well.

If i understand you correctly, then I'd hate to see you use a hammer, or axe, or any other tool. Does the handle move at the same speed as the end point?

[5263]

Originally Posted by chico9166

Does the handle move at the same speed as the end point?

This is exactly what we are trying to avoid from traditional tennis.

Not sure how you got that from me saying the hand is what we directly control, but the control of the hand and the technique is what brings the racket face around with acceleration beyond the hand.
We don't have direct control of the racket face, but control thru technique and
via the handle thru the shaft.

[TennisCJC]

Man, this has gone off the deep end.

If you want to hit a controlled rally shot, accelerate thru the contact zone with a smooth stroke. If you want to hit a harder shot, accelerate thru the the contact zone at a faster pace. Neither is slow and neither is out of control. The concept of accelerating thru eliminates deceleration which is the kiss of death on groundstrokes and serves.

I think the charts and graphs probably say the same thing but they hurt my head. Swing thru the damn ball and finish strong.

[5263]

Originally Posted by TennisCJC

Man, this has gone off the deep end.

If you want to hit a controlled rally shot, accelerate thru the contact zone with a smooth stroke. If you want to hit a harder shot, accelerate thru the the contact zone at a faster pace. Neither is slow and neither is out of control. The concept of accelerating thru eliminates deceleration which is the kiss of death on groundstrokes and serves.

I think the charts and graphs probably say the same thing but they hurt my head. Swing thru the damn ball and finish strong.

Pretty good way to say it.

[sureshs]

Double pendulum seems to be the wrong model. Look at the clip - the bar representing the lower arm almost stops while the racket continues moving up into the ball. It happens because the racket has energy from its swing on the other side.

Now, try to hit a top spin forehand by decelerating and then stopping the lower arm when it is about vertical and tell me whether the racket moved up by itself and hit the ball!

That is why you get the wrong plot that hand velocity is 0 when racket velocity is maximum.

I have objected to the pendulum analysis when it was put forward in the polarization threads.

[5263]

Originally Posted by sureshs

Double pendulum seems to be the wrong model. Look at the clip - the bar representing the lower arm almost stops while the racket continues moving up into the ball. It happens because the racket has energy from its swing on the other side.

Now, try to hit a top spin forehand by decelerating and then stopping the lower arm when it is about vertical and tell me whether the racket moved up by itself and hit the ball!

.

I was noticing this too.
You can do it and many beginners start something like this with very poor results, lol.

[sureshs]

Originally Posted by 5263

I was noticing this too.
You can do it and many beginners start something like this with very poor results, lol.

In the light racket clip, the racket does not move up much. I was kind of OK with that, except I felt what purpose does it serve. Then the heavy racket clip showed the racket moving up much more, and again I was like, OK, but who hits the ball like that?

I can imagine that this model MIGHT describe a golf put, but not a tennis shot. Even feeding the ball requires more effort than that.

The hand and the racket have to move together - one cannot stop and hope that inertia will swing the racket up into the ball just by keeping a loose wrist.

[5263]

Originally Posted by sureshs

Double pendulum seems to be the wrong model. Look at the clip - the bar representing the lower arm almost stops while the racket continues moving up into the ball. It happens because the racket has energy from its swing on the other side..

THis is also why I did not feel I could depend on the data, especially
in reference to the hand slowing in the graph.
I think with a true modern swing, you will see the speed stay up there better
with the hands and the racket, also
for a slightly longer time than Cross' graph shows.

[sureshs]

Originally Posted by 5263

THis is also why I did not feel I could depend on the data, especially
in reference to the hand slowing in the graph.
I think with a true modern swing, you will see the speed stay up there better
with the hands and the racket, also
for a slightly longer time than Cross' graph shows.

I think it was a case of picking the only studied mathematical problem which even remotely resembles the real case. You see this in textbooks, where the purpose is to give the student a very broad idea of the actual thing to help them visualize. But in this case, the analysis does not seem to be useful to anyone.