"Accelerate evenly through the ball"

Bergboy123 · Apr 27, 2012

I saw someone on these forums say "accelerate EVENLY through the ball" on groundstrokes. I tried it today and liked the results.

I know this sounds elementary, but I realized that I tend to accelerate quickly up until contact with the ball but then I eased off the acceleration and let momentum carry the stroke through.

I went out and specifically made it a very fluid and equal motion from start to finish, without slowing down until my arm was across my chest, and with my forehand especially I felt like it made it better. Definitely seemed to give me a bit more depth and control.

Has anyone else thought of this? Was I the only one who didn't know this fact?

LeeD · Apr 27, 2012

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.

Cheetah · Apr 27, 2012

Bergboy123 said:
I saw someone on these forums say "accelerate EVENLY through the ball" on groundstrokes. I tried it today and liked the results.

I know this sounds elementary, but I realized that I tend to accelerate quickly up until contact with the ball but then I eased off the acceleration and let momentum carry the stroke through.

I went out and specifically made it a very fluid and equal motion from start to finish, without slowing down until my arm was across my chest, and with my forehand especially I felt like it made it better. Definitely seemed to give me a bit more depth and control.

Has anyone else thought of this? Was I the only one who didn't know this fact?

sounds like with your new stroke you are swinging at the same, constant speed thru the whole stroke. if that's what you did then probably this eliminated some flaw you had and probably your rhs was slower so you were more consistent or whatever.

however, if you want to strike ball correctly you should be accelerating from slot position through contact. that means the rhs should be always increasing. you want a 'constate rate of acceleration'. not a 'constant swing speed' which is what it sounds like you are doing. doing it that way you will have a slower rhs and less control because you will be swinging as fast as you can from the start. not good.

the racquet head should be accelerating as you make contact. that means the racquet is going faster at contact than it was 5 cm before contact. and rhs at 5cm before contact is faster than it was 15 cm before contact and so on and so on.

ipodtennispro · Apr 27, 2012

Flat or topspin?

Bergboy123 said:
I saw someone on these forums say "accelerate EVENLY through the ball" on groundstrokes. I tried it today and liked the results.

I know this sounds elementary, but I realized that I tend to accelerate quickly up until contact with the ball but then I eased off the acceleration and let momentum carry the stroke through.

I went out and specifically made it a very fluid and equal motion from start to finish, without slowing down until my arm was across my chest, and with my forehand especially I felt like it made it better. Definitely seemed to give me a bit more depth and control.

Has anyone else thought of this? Was I the only one who didn't know this fact?

This sounds like a very old school type forehand. Yes, this is a good idea if you are opening the racket face and you are just lifting the ball, otherwise you will be retrieving balls over the back fence if you accelerate the finish.

This is bad idea if you are trying to learn any type of topspin. As Cheetah mentioned, there is never one speed throughout the swing. In fact, you want to get some kind of whip rhythm at the finish.

fuzz nation · Apr 28, 2012

Without seeing you hit some shots, it sounds as though you were thinking about swinging through contact instead of only to contact. That's really important for getting a good, consistent aspect on your racquet through the hitting zone, but it doesn't necessarily happen naturally for everyone.

Think about how the racquet passes your arm and hand more quickly when you stop accelerating your swing at one point or another. As the racquet "releases" in that action of passing your gripping hand, it sort of turns over as it travels forward. Accelerating though the contact zone is better for making that "turning over" of the racquet happen more consistently - depending on your swing, it might even delay that action until later in your stroke.

Compare that swing to another where your racquet is in the middle of turning over more quickly while it's in the hitting zone (only accelerating to the ball). Meeting the ball with a predictable angle on your racquet face becomes a lot more tricky that way. If your acceleration quits a little early or a hair late, the racquet angle won't be the same. Getting much control with that sort of hitting demands timing that's almost impossible to sustain.

5263 · Apr 28, 2012

Cheetah said:
sounds like with your new stroke you are swinging at the same, constant speed thru the whole stroke.

however, if you want to strike ball correctly you should be accelerating from slot position through contact. .

I'm hoping you misunderstood him here. He seems like he was trying to take Limps good advice of using a steady "Accel" into the ball, much like you describe in the last sentence above.
THe way he wrote it leaves it unclear though, so maybe he will come back and straighten this out for us.

Bergboy123 · Apr 28, 2012

Sorry for the confusion guys. Yes, with my new stroke I indeed was continuing acceleration and swinging faster and faster throughout the stroke. What was new was that I continued speeding up AFTER contact with ball, whereas before I would accelerate to contact but then just kinda stop and flick my wrist a little bit.

pvaudio · Apr 28, 2012

I would say that's a good intuitive tool, but not exactly accurate. Accelerate through contact, and then let the racquet follow through. If you try to force the follow through, you'll end up muscling the whole stroke.

5263 · Apr 28, 2012

pvaudio said:
I would say that's a good intuitive tool, but not exactly accurate. Accelerate through contact, and then let the racquet follow through. If you try to force the follow through, you'll end up muscling the whole stroke.

I would just say I don't find that the case in my instruction and play, but
things my work different for some and based on the instruction as a whole.

tlm · Apr 28, 2012

Bergboy123 said:
Sorry for the confusion guys. Yes, with my new stroke I indeed was continuing acceleration and swinging faster and faster throughout the stroke. What was new was that I continued speeding up AFTER contact with ball, whereas before I would accelerate to contact but then just kinda stop and flick my wrist a little bit.

This sounds to me like you are doing it correctly. I think that if the acceleration is started to early it can cause problems, but right before during and after you hit the ball you should be accelerating.

SystemicAnomaly · Apr 29, 2012

It's all an illusion. I do not believe that it is possible to increase the speed (the tangential velocity) of the racquet during contact. If I understand the physics of the collision correctly, the racquet head loses tangential speed (and angular speed?) at contact. However, the hand/wrist holding the racquet does not necessarily lose speed.

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

Also consider the conservation of momentum:

https://www.msu.edu/~jochmans/physicsoftennis.html
.

5263 · Apr 29, 2012

SystemicAnomaly said:
It's all an illusion. I do not believe that it is possible to increase the speed (the tangential velocity) of the racquet during contact. If I understand the physics of the collision correctly, the racquet head loses tangential speed (and angular speed?) at contact. However, the hand/wrist holding the racquet does not necessarily lose speed.

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

.

Really like that graphic.
Shows how the racket speed is increase going around the horn there due to having to keep up with the hand while traveling a longer distance than the hand, which results in greater speed for that segment. Once it makes that
wide turn at speed it is back to normal speed.
I don't see the illusion though. The hand/handle is what we have to control and direct when pulling the head, which is then affected.
Racket head is so much like a water skier outside the wake in a turn. That is fun to do and the force out there is quite a kick.

But back to the point, the hand is what we intend to accel thru contact. If we
make that effort, it matters little where it slows or stays constant. If we don't make that effort that will have an effect though.

julian · Apr 29, 2012

Do me a favour

SystemicAnomaly said:
It's all an illusion. I do not believe that it is possible to increase the speed (the tangential velocity) of the racquet during contact. If I understand the physics of the collision correctly, the racquet head loses tangential speed (and angular speed?) at contact. However, the hand/wrist holding the racquet does not necessarily lose speed.

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

Also consider the conservation of momentum:

https://www.msu.edu/~jochmans/physicsoftennis.html
.

Hi,
please go to
http://www.physics.usyd.edu.au/~cross/publications.html
please click the title of the paper
R. Cross, A double pendulum model of tennis strokes, Am. J. Phys. 79, 470-476 (2011). See also http://twu.tennis-warehouse.com/learning_center/doublependulum.php for videos of double pendulum action.
Please see Fig 4
The lower curve address the topic of your post in the case of the angular velocity ( FOR THE ELASTIC COLLISION)
Please let me know whether it helps in any way
http://twu.tennis-warehouse.com/learning_center/doublependulum.php
illustrates the same point
Please see Figure 10.

julian · Apr 29, 2012

Angular velocity

5263 said:
Really like that graphic.
Shows how the racket speed is increase going around the horn there due to having to keep up with the hand while traveling a longer distance than the hand, which results in greater speed for that segment. Once it makes that
wide turn at speed it is back to normal speed.
I don't see the illusion though. The hand/handle is what we have to control and direct when pulling the head, which is then affected.
Racket head is so much like a water skier outside the wake in a turn. That is fun to do and the force out there is quite a kick.

But back to the point, the hand is what we intend to accel thru contact. If we
make that effort, it matters little where it slows or stays constant. If we don't make that effort that will have an effect though.

To be exact:
1.Angular velocity of the HAND is max around .6 of sec BEFORE the contact
2.Next it gets slower/smaller close to contact
3.Next it gets bigger after the contact
See a picture from my post above (it resembles the letter V)
Please note the word HAND above
Another variable is the fact that THE INCOMING BALL has some speed

5263 · Apr 29, 2012

julian said:
Hi,
please go to
http://www.physics.usyd.edu.au/~cross/publications.html
please click the title of the paper
R. Cross, A double pendulum model of tennis strokes, Am. J. Phys. 79, 470-476 (2011). See also http://twu.tennis-warehouse.com/learning_center/doublependulum.php for videos of double pendulum action.
Please see Fig 4
The lower curve address the topic of your post in the case of the angular velocity ( FOR THE ELASTIC COLLISION)
Please let me know whether it helps in any way

Cross's work does seem to indicate some racket accel up until just after impact.

5263 · Apr 29, 2012

julian said:
To be exact:
1.Angular velocity of the HAND is max around .6 of sec BEFORE the contact
2.Next it gets slower/smaller close to contact
3.Next it gets bigger after the contact
See a picture from my post above (it resembles the letter V)
Please note the word HAND above

But the racket is fastest just after contact on the double pendulum, right?
top of pg 474

julian · Apr 29, 2012

It is more or less correct

5263 said:
Cross's work does seem to indicate some racket accel up until just after impact.

The ANGULAR SPEED of the RACKET resembles the inverted V
i.e
1.it grows BEFORE contact
2.it has the MAX at the contact
3.it decreases AFTER the contact
Rod says that his results/calculations are confirmed by biomechanical data
I do NOT have data about the TANGENTIAL speed of either THE RACKET or the HAND.
Therefore I do NOT know whether the second sentence of the post #11 above is valid or NOT.
Once more:
another variable is the fact that THE INCOMING BALL has some speed

5263 · Apr 29, 2012

julian said:
The ANGULAR SPEED of the RACKET resembles the inverted V
i.e
1.it grows BEFORE contact
2.it has the MAX at the contact
3.it decreases AFTER the contact
Rod says that his results/calculations are confirmed by biomechanical data
I do NOT have data about the TANGENTIAL speed of either THE RACKET or the HAND

Check for me on p.474
doesn't the inverted V go still higher after contact?
for just a bit?
doesn't that mean max is just after contact?

julian · Apr 29, 2012

I can agree with what you are saying

5263 said:
Check for me on p.474
doesn't the inverted V go still higher after contact?
for just a bit?
doesn't that mean max is just after contact?

I can agree with what you are saying.
Switching gears:
The basic problem with the OP was that there was NO DEFINITION
of the phrase
"accelerate EVENLY through the ball"
The partial answers above bring as closer to the issue but one should take the ball into account as well.
The original question is OK if one can define the question a bit better.
It comes without saying that similar questions can be phrased for the SERVE AS WELL.
The role of the WRIST is "hidden" somehow as well

The paper quoted simplifies the movement to:
1.two dimensions ONLY
2.BALANCED rackets only,I believe

julian · Apr 29, 2012

acceleration is NOT CONSTANT

5263 said:
Check for me on p.474
doesn't the inverted V go still higher after contact?
for just a bit?
doesn't that mean max is just after contact?

BTW: acceleration is NOT CONSTANT NEITHER for THE HAND or THE RACKET

5263 · Apr 29, 2012

julian said:
BTW: acceleration is NOT CONSTANT NEITHER for THE HAND or THE RACKET

Lay people and even scientist don't always word things just right.

Like here for instance. Do you mean it is not constant in Cross's work or

that is cannot be constant?

I would say that no speed is truly constant, therefore these "constant" changes
in speed would indicate that acceleration (change in speed) is the constant state of things. I mean if you want to get picky like that?

My point is that I think that the OP is trying to say that he means to accel slightly
before, thru the contact phase and slightly beyond.

julian · Apr 29, 2012

Two places

5263 said:
Lay people and even scientist don't always word things just right.

Like here for instance. Do you mean it is not constant in Cross's work or

that is cannot be constant?

I would say that no speed is truly constant, therefore these "constant" changes
in speed would indicate that acceleration (change in speed) is the constant state of things. I mean if you want to get picky like that?

My point is that I think that he is trying to say that he means to accel slightly
before, thru the contact phase and slightly beyond.

1.The Rod's work says that acceleration is NOT constant in THE CASE of
angular speed.
It is worse than this-acceleration is changing SIGN for both the hand and the racket
2.He says that his graphs are "documented in the literature"
I understand that he means pro players observation but I could be wrong

julian · Apr 29, 2012

A very minor comment

SystemicAnomaly said:
It's all an illusion. I do not believe that it is possible to increase the speed (the tangential velocity) of the racquet during contact. If I understand the physics of the collision correctly, the racquet head loses tangential speed (and angular speed?) at contact. However, the hand/wrist holding the racquet does not necessarily lose speed.

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

Also consider the conservation of momentum:

https://www.msu.edu/~jochmans/physicsoftennis.html
.

Hi,
I believe there are two POSSIBLE models:
1.an elastic collision - the conservation of momentum is satisfied
2.an inelastic collision-a ball is deformed during the collision
the conservation of momentum is NOT satisfied

5263 · Apr 29, 2012

julian said:
1.The Rod's work says that acceleration is NOT constant in THE CASE of
angular speed.
It is worse than this-acceleration is changing SIGN for both the hand and the racket
2.He says that his graphs are "documented in the literature"
I understand that he means pro players observation but I could be wrong

When I said he in the last post, I should have stated the poster who made the OP related to constant accel-- not Cross.
I will edit.

Limpinhitter · Apr 29, 2012

Bergboy123 said:
I saw someone on these forums say "accelerate EVENLY through the ball" on groundstrokes. I tried it today and liked the results.

I know this sounds elementary, but I realized that I tend to accelerate quickly up until contact with the ball but then I eased off the acceleration and let momentum carry the stroke through.

I went out and specifically made it a very fluid and equal motion from start to finish, without slowing down until my arm was across my chest, and with my forehand especially I felt like it made it better. Definitely seemed to give me a bit more depth and control.

Has anyone else thought of this? Was I the only one who didn't know this fact?

IMO, accelerating too early in the swing, or too abruptly, is a common error among many players, even higher level rec players. I would describe the better approach as a gradual acceleration through contact. One effective way to accomplish that is to delay acceleration until just before contact. That description seems to help players achieve the execution of gradual acceleration.

5263 · Apr 29, 2012

Limpinhitter said:
IMO, accelerating too early in the swing, or too abruptly, is a common error among many players, even higher level rec players. I would describe the better approach as a gradual acceleration through contact. One effective way to accomplish that is to delay acceleration until just before contact. That description seems to help players achieve the execution of gradual acceleration.

well stated...

pvaudio · Apr 29, 2012

5263 said:
I would just say I don't find that the case in my instruction and play, but
things my work different for some and based on the instruction as a whole.

SystemicAnomaly said:
It's all an illusion. I do not believe that it is possible to increase the speed (the tangential velocity) of the racquet during contact. If I understand the physics of the collision correctly, the racquet head loses tangential speed (and angular speed?) at contact. However, the hand/wrist holding the racquet does not necessarily lose speed.

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

Also consider the conservation of momentum:

https://www.msu.edu/~jochmans/physicsoftennis.html
.

5263, this is exactly what I was implying without wanting to start another physics discussion. Since it's not exactly impossible, but absolutely pointless to continue accelerating after contact, I don't want people to end up swinging extra hard just to get that effect. Rather, what you're implying is in fact right. It's more or less swinging through the stroke and not braking it after contact. I've seen many fellow club players swing hard through the ball to get that effect, while the ball coming off the college players is 100x bigger and they simply let their body take the racquet through and decelerate naturally. Nonetheless, I'm with you, just wanted to put that in a different wording so people don't start arming their strokes.

pvaudio · Apr 29, 2012

And guys, as much as I love sciency stuff, the physics papers really aren't necessary here. This is why: it's very easy to get mixed up with your terms. Velocity and acceleration, while closely related, are extremely different concepts. I'm assuming you know this already. The reason the literature is going to add confusion is that for your pendulum thing, the acceleration is at its minimum when your velocity is at its highest. If you apply that to a tennis stroke, that means that you should have stopped accelerating the racquet so that you have max RHS at contact. That is correct. The notion by the OP, however, is to accelerate through the ball. This gives you nothing but the potential to start muscling the ball. By simply saying swing through the entire stroke, you'll get the exact same result without the confusion. Hope that made what I was saying clearer.

pvaudio · Apr 29, 2012

Bergboy123 said:
I saw someone on these forums say "accelerate EVENLY through the ball" on groundstrokes. I tried it today and liked the results.

I know this sounds elementary, but I realized that I tend to accelerate quickly up until contact with the ball but then I eased off the acceleration and let momentum carry the stroke through.

I went out and specifically made it a very fluid and equal motion from start to finish, without slowing down until my arm was across my chest, and with my forehand especially I felt like it made it better. Definitely seemed to give me a bit more depth and control.

Has anyone else thought of this? Was I the only one who didn't know this fact?

This is exactly it. If it's a fluid and equal motion from start to finish, there is zero acceleration through the stroke. The RHS is constant. In other words, you accelerated the racquet up to your desired RHS, kept it there and hit through the ball. That's what you want. When people talking "generating racquet head speed", they're talking about the acceleration of the racquet. That occurs before contact only.

chico9166 · Apr 29, 2012

Limpinhitter said:
IMO, accelerating too early in the swing, or too abruptly, is a common error among many players, even higher level rec players. I would describe the better approach as a gradual acceleration through contact. One effective way to accomplish that is to delay acceleration until just before contact. That description seems to help players achieve the execution of gradual acceleration.

Agree with this, and I believe the RHS profiles will back this up as the bulk occurs shortly before contact. I too have seen tempo/timing messed up due to a desire to get the racquet moving too early in the forward swing.(and worse yet in the transition stage)

In my mind as the racquet starts to change directions(from downward to forward) there is almost a feeling of suppressing RHS as one tries to line up the ball. And then "releasing" the racquet/arm as close to contact as possible.

julian · Apr 29, 2012

Power release in golf

5263 said:
well stated...

see as well
http://perfectgolfswingreview.net/HandRelease.htm

sureshs · Apr 29, 2012

You can hit a pretty decent and solid old-style flattish shot with a uniform smooth swing. But if you want topspin, such a swing will result in a very weak sitter. You have to accelerate into the stroke for top-spin.

SystemicAnomaly · Apr 29, 2012

5263, the illusion that I was referring to is that the racket head speed does not increase during/after contact as the OP and others appeared to imply. It looks like I opened up a whole can of worms with my "illusion" post.

julian said:
Hi, please go to
http://www.physics.usyd.edu.au/~cross/publications.html
please click the title of the paper
R. Cross, A double pendulum model of tennis strokes, Am. J. Phys. 79, 470-476 (2011). See also http://twu.tennis-warehouse.com/learning_center/doublependulum.php for videos of double pendulum action.
Please see Fig 4
The lower curve address the topic of your post in the case of the angular velocity ( FOR THE ELASTIC COLLISION)
Please let me know whether it helps in any way
http://twu.tennis-warehouse.com/learning_center/doublependulum.php
illustrates the same point
Please see Figure 10.

Thanks for the links, julian. It was 4 in the morning when I wrote that post, my brain was in a fog and I was having trouble trying to find something by Rod Cross in his book, Technical Tennis. Did not find exactly what I was looking for.

julian said:
Hi,
I believe there are two POSSIBLE models:
1.an elastic collision - the conservation of momentum is satisfied
2.an inelastic collision-a ball is deformed during the collision
the conservation of momentum is NOT satisfied

Actually momentum is conserved for both type of collisions. It is kinetic energy that is not conserved for inelastic collisions. Some heat (energy) is lost due to compression.

As a side note, the coefficient of restitution (COR) for a ball-racket (string) collision is about 0.4 whereas an elastic collision would have a COR =1 (and a perfectly inelastic collision, where the 2 objects remain stuck together, would have a COR = 0).

Ain't science wonderful? I l love how physics tends to violate intuition.
.

SystemicAnomaly · Apr 29, 2012

pvaudio said:
5263, this is exactly what I was implying without wanting to start another physics discussion. Since it's not exactly impossible, but absolutely pointless to continue accelerating after contact, I don't want people to end up swinging extra hard just to get that effect...

Good points. Yes, I suppose it is possible to accelerate the racket head again after contact but, as you say, it is probably pointless and possibly detrimental to the arm.

Limpinhitter said:
IMO, accelerating too early in the swing, or too abruptly, is a common error among many players, even higher level rec players. I would describe the better approach as a gradual acceleration through contact. One effective way to accomplish that is to delay acceleration until just before contact. That description seems to help players achieve the execution of gradual acceleration.

julian said:
see as well
http://perfectgolfswingreview.net/HandRelease.htm

A lot of interesting stuff in this thread. But it may be more than the OP bargained for.
.

netguy · Apr 29, 2012

Gradual accelaration goes hand in hand with hitting through the ball.

5263 · Apr 29, 2012

SystemicAnomaly said:
5263, the illusion that I was referring to is that the racket head speed does not increase during/after contact as the OP and others appeared to imply. It looks like I opened up a whole can of worms with my "illusion" post.

Ain't science wonderful? I l love how physics tends to violate intuition.
.

I get your point and was prepared to accept that illusion, but I do think he was speaking more of his intention than his true action, but I could be wrong.

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.

julian · Apr 29, 2012

Illusion

SystemicAnomaly said:
5263, the illusion that I was referring to is that the racket head speed does not increase during/after contact as the OP and others appeared to imply. It looks like I opened up a whole can of worms with my "illusion" post.

Thanks for the links, julian. It was 4 in the morning when I wrote that post, my brain was in a fog and I was having trouble trying to find something by Rod Cross in his book, Technical Tennis. Did not find exactly what I was looking for.

Actually momentum is conserved for both type of collisions. It is kinetic energy that is not conserved for inelastic collisions. Some heat (energy) is lost due to compression.

As a side note, the coefficient of restitution (COR) for a ball-racket (string) collision is about 0.4 whereas an elastic collision would have a COR =1 (and a perfectly inelastic collision, where the 2 objects remain stuck together, would have a COR = 0).

Ain't science wonderful? I l love how physics tends to violate intuition.
.

You raised probably NOT by design couple more interesting points from the point of view of coaching
1.do we attempt to deaccelarate a racket after the contact?
2.what does it mean "during the contact"?
Is it 2-4 milliseconds?
3.Does the angular speed of a racket relate easy to the angular speed of the arm?
4.What is the role of the wrist if the arm plus the arm is slower than the racket?
5.Is the balance of the racket important for #1,#3 and #4 above?
6.What do we explain to a student teaching forehand AND/OR serve?
7.If you say "momentum is preserved" you have to specify the system
of which the momentum is preserved
Is it the arm plus the wrist plus the ball (with the air inside) plus the racket/frame plus strings?

SystemicAnomaly · Apr 29, 2012

5263 said:
I get your point and was prepared to accept that illusion, but I do think he was speaking more of his intention than his true action, but I could be wrong.

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.

Yes, I can appreciate your comment about the OP's intent.

Which charts, in particular, are your referring to? Fig 10 on this page shows that the angular velocity (magnitude) of the racket decreases after contact while the angular arm velocity increases again.

I'm a bit reluctant to use the term, acceleration, since it is a vector. Acceleration describes the rate of change of both the magnitude and the direction of velocity. The magnitude of the velocity can be constant while the direction is changing -- this would still be considered acceleration.

julian · Apr 29, 2012

The Annals of Physics paper

SystemicAnomaly said:
Yes, I can appreciate your comment about the OP's intent.

Which charts, in particular, are your referring to? Fig 10 on this page shows that the angular velocity (magnitude) of the racket decreases after contact while the angular arm velocity increases again.

I'm a bit reluctant to use the term, acceleration, since it is a vector. Acceleration describes the rate of change of both the magnitude and the direction of velocity. The magnitude of the velocity can be constant while the direction is changing -- this would still be considered acceleration.

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

SystemicAnomaly · Apr 29, 2012

julian said:
You raised probably NOT by design couple more interesting points from the point of view of coaching
1.do we attempt to deaccelarate a racket after the contact?
2.what does it mean "during the contact"?
Is it 2-4 milliseconds?
3.Does the angular speed of a racket relate easy to the angular speed of the arm?
4.What is the role of the wrist if the arm plus the arm is slower than the racket?
5.Is the balance of the racket important for #1,#3 and #4 above?
6.What do we explain to a student teaching forehand AND/OR serve?

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.

SystemicAnomaly · Apr 30, 2012

5263 said:
... 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.

julian said:
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/~cross/PUBLICATIONS/49.%20TennisDPend.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/learning_center/doublependulum.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 · Apr 30, 2012

Forget the physics...

...this is what matters...

LeeD said:
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 · Apr 30, 2012

Babolat Play &Connect

SystemicAnomaly said:
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=p913fGx6zV4&feature=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/201...onnect-data-straight-from-your-tennis-racket/
http://tt.tennis-warehouse.com/showthread.php?t=419169
http://tt.tennis-warehouse.com/showthread.php?t=412968

5263 · Apr 30, 2012

SystemicAnomaly said:
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 · Apr 30, 2012

"not intend to accel"

5263 said:
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 · Apr 30, 2012

julian said:
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 · Apr 30, 2012

Did you answer my FIRST question?

5263 said:
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 · Apr 30, 2012

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

Hand/handle, as
that is what we manipulate.

julian · Apr 30, 2012

So we have a SIGNIFICANT DISAGREEMENT

5263 said:
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 · Apr 30, 2012

julian said:
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.

"Accelerate evenly through the ball"

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