Soderling's Backhand; Video Available?

[johnyandell]

Ah another victim. Go for it and enjoy the wallow!

[airforce1]

Ah another victim. Go for it and enjoy the wallow!

Waters is going to come get you yet! LoL

[johnyandell]

Nah, he maned up...

[sejsel]

Thank you to both Brian Gordon and Rosooki for contributing your physics knowledge to this post.



I thought you were finally going to make my point at the end of your post, but instead you just made a flippant comment like many others here have chosen to do.

Not really in my eyes, they were just giving a sligthly different view, or set of arguments on the issue.
I will have to recheck through the posts you are referring to, though.
Just a first impression....

The main point I've been trying to make all along here is that if a heavier mass moves at the same rate of acceleration (or velocity) as a lighter mass, the heavier mass will contain more force (or kinetic energy) than the lighter mass will. I believe that this additional force is in the form of inertia.

Yes, but applied to this case you have to take into account the mass, or to be entirely correct (and this can be vastly different than only the mass of the tennis ball) the kinetic energy of the incoming ball.
To make the issue even more complex, please do read the material on the experience of the people trying to return Pete Sampras serve.
It appeared to one of them that he was trying to return baseball rather than tennis ball.
It says something about kinetic energy of the object vs. only its mass. (or even objects f = m * a)

In tennis terms this means that if a heavy player can swing the racket with the same amount of acceleration (and speed) as a lighter player, he will impart more force (and kinetic energy) onto the ball. Yes, this will take more effort, as BG pointed out earlier, but the effort will be rewarded with a ball that is struck harder.

Not really. The heavier player can only hit harder ball if he, due to the mass and strength of his body parts combined throughout the whole biomechanical chain (from legs upwards to the racket and the ball) does manage to create greater amount of "acceleration" (and the resulting speed eventually, which is the determining factor - much more than the acceleration, which is really a rate of increase of speed in given time interval, or frame) than the other person.
Heavier player has theoretically better chance of doing this, but only if he can translate his mass and strength into the greater resulting speed of the racquet of the same mass than the other person.
I think that Rod Cross is spot on on this point.

This applies with either the force or the kinetic energy equation, although weight is obviously less of a factor in the kinetic energy equation. This was the essence of what I've been trying to say all along here, but for some reason people are either unwilling to or unable to understand that.

And although I agree that kinetic energy is very important in tennis, I don't think it's the only relevant form of energy. There's also the amount of force that the player absorbs with his/her arm/s. Anyone who has ever suffered from tennis elbow can tell you that that is a pretty significant force. As you know this amount of force partially determines (along with kinetic energy) how much the racket will decelerate upon impact, which in turn is a factor in determining how much force will be imparted on the ball.

When talking about these issues in this manner, one has to be very carefull, and quantify the elements and their rate or amount in these equations.

When talking about the force, and "partial application" of absorption and resulting deceleration, it is simply not enough to just give one's more or less intuitive comprehension of how great a role they play in the resulting stroke.
We are talking numbers here, and assuming the racquet of about 12 oz. in weight, and tennis balls as they are, we can have a starting point for some calculations.

No, the kinetic energy is not the only element, but it is much more significant then mass of the players arm, or even the mass of the whole player (again, to a reasonable extent).
But even this has to be put in proportion and in some frame of the masses of the elements involved.
This always brings me to the dear subject of numerical analysis...

I think you would agree, especially if you've ever hit a 2 handed-backhand, that this force that is absorbed by the arm/s is significantly greater with the 2hbh,

This really doesn't make much sense.
If we are talking about the same force, than it is distributed on two arms, in some proportion depending on ratio of the dominant/non dominant arm participation in the shot, force-wise.

in which the non-dominant arm absorbs the brunt of the force,

Really? How come? It is the dominant arm which is, acording to any player, leading the shot and hitting the ball, while non-dominant is "helping out".
It should be clear then which arm should "absorb" the brunt of the force.

than with either the 1hbh or forehand. The increased energy absorption in the 2hbh is related to the shorter levers (arms) and slower racket speed/acceleration.

True only to some extent (shorter levers), but not in all cases - there are variations in extensions and individual techniques. I agree to some point.

Also, the statement about slower racket speed/acceleration on double hander is highly debatable, if not untrue.

Since velocity isn't a factor,

Let's not kid with the facts, velocity is always a factor.

the amount of force the arm absorbs must be a function of the f = m * a equation, not the k = 1/2 m * a^2 equation.

Wrong deduction, and the equation k = 1/2 m * v^2 (not a ^ 2 ) is the right one.
We should be talking kinetic energy (energy of the moving object) rather than the force as f = m * a - read again one of the posts referring to this, which is explaining how and why.

That's why body weight plays an even greater role in determining the force imparted on the ball with a 2hbh than with either a 1hbh or forehand. And, as I've said before, that's the main reason why the massive Nalbandian has such a great 2hbh.

For all his mass, Nalbandian is able to hit such a great bh due to many more other things than that.
His mass is not the main reason for the end result, nor should it play bigger or lesser role if he was hitting the one hander, for that matter.

Also, since mass is a factor in both of these equations (force and acceleration), when John said:



... he was wrong.

Only if we assume that the equation k = 1/2 m * v^2 is not applicable here.
But please, let's leave this to physicists, who would probably laugh their lives out on parts of this debate.

I am repeating, we are talking numbers and applied physics here.

I don't think that Rod Cross was born yesterday in that regard either.

[crass_lawner]

I was prepared to let this thread die, but you've left me no choice.

When talking about the force, and "partial application" of absorption and resulting deceleration, it is simply not enough to just give one's more or less intuitive comprehension of how great a role they play in the resulting stroke.

If an arm attached to a heavier body slows down deceleration AT ALL then Rod Cross is wrong. The exact amount of deceleration would of course require measurements and equations, but isn't necessary to determine the veracity of Mr. Cross's claim. Brian Gordon (another sport biomechanist) acknowledged that weight is transferred from the body to the racket, so that right there is at odds with Mr. Cross's claim, since obviously a racket with more weight (inertia) is going to decelerate less upon contact.

It is the dominant arm which is, acording to any player, leading the shot and hitting the ball, while non-dominant is "helping out".
It should be clear then which arm should "absorb" the brunt of the force.

Yes the dominant hand is leading the ball, both hands are "hitting" the ball, but the non-dominant hand is absorbing the brunt of the force, or else Paul Annacone and Mary Joe Fernandez aren't tennis players.

Paul Annocone's opinion.

http://tennis.com/yourgame/askpaulannacone/askpaul.aspx?id=1230

Mary Joe Fernandez commenting on Caroline Wozniacki's backhand. Picture #4.

http://www.tennis.com/yourgame/instructionarticles/backhand/backhand.aspx?id=163890

Let's not kid with the facts, velocity is always a factor.

No, actually velocity isn't a factor in the force = mass * acceleration equation. Force mass and acceleration are.

My quote:

the amount of force the arm absorbs must be a function of the f = m * a equation, not the k = 1/2 m * a^2 equation.

Your quote:

Wrong deduction, and the equation k = 1/2 m * v^2 (not a ^ 2 ) is the right one.
We should be talking kinetic energy (energy of the moving object) rather than the force as f = m * a - read again one of the posts referring to this, which is explaining how and why.

Yes you are correct. What I should have written is that the force the arm uses to counter the force of the tennis ball would be a function of the F = M * A equation.

I wrote:

Also, since mass is a factor in both of these equations (force and acceleration), when John said:

Intuitively working with players it's obvious the whole weight issue is a non factor, but proving it is beyond my expertise and I am afraid also that of the posters here.

... he was wrong.

You wrote:

Only if we assume that the equation k = 1/2 m * v^2 is not applicable here.
But please, let's leave this to physicists, who would probably laugh their lives out on parts of this debate.

I am repeating, we are talking numbers and applied physics here.

Why couldn't k = 1/2 m * v^2 be applicable? Mass is obviously a factor in that equation as well as the force equation. If you need a physicist to tell you that then you're in trouble. You don't always need numbers to perform mathematics. A positive number times a positive number yields a positive number. There I just did some math. The math and logic I'm employing here aren't much more complicated than that.

I think I've already explained everything else you've brought up in previous threads, so I'll leave it up to you to figure those things out if you want to.

[sejsel]

Crass, you are missreading what I wrote, and as well possibly missreading what Paul Annacone wrote - or we are using different terminology.

Dominant arm is the one leading through the shot, and "hitting the ball"; one of the ways double hander is taught is (in case of right handers) to primarily learn to hit left-handed forehand. Annacone is not saying anything explicitly about distribution of the force met by the player in terms we are discussing here (other that referring to the right hand of the player in question as the dominant) - he is giving the help in terms of getting the feel for the swing and path of the racquet through the swing and "through the ball".
The player asking the question is having his right arm as dominant, clearly indicated by his grip with the right hand.
This is not always the case - many players have the other version, where left hand is dominant and leading through the shot.

You seem to be convinced that f=m*a is the equation applicable here - I am convinced that k=1/2mv^2 is (kinetic energy of the moving object - tennis racquet) is the one applicable here, and not f=m*a in first case.
When talking about moving object - one takes the first derivative of the f = m*a, or d/dt of f = m*a, derivative in regard to the time, which yields d/dt(F) = m * d/dt(v/t) (where of course v/t = a, and m is a constant), and that is 1/2mv^2 = k.

Racquet is a moving object when hitting the ball.
Its mass does play a role, of course, but everything has to be clearly put in the right frame of values here.


The distinction between these two equations has been clearly explained to you by other member of the forum (rosooki, I believe) - you are not recognizing it s fully valid in regard to f=m*a - fine.

Go to universities and consult physicists and let's see what they say.

My last remark (in my previous post) was referring to this portion of the debate rather than directly to what John wrote (since that part wasn't visible at all in the page when I wrote the first post), although I think he was to a large extent right when it comes to the weight of the player as a factor.

I have read through the debate, the post I referred to (from you) stuck in my eyes as being "incorrect" in a number of statements.

It really boils down to not much more than physics 101.

I can adress your answer sentence by sentence later on, this is just the short version.

[airforce1]

from Rod Cross' work

Several items from the Master, Rod Cross' work that cast doubt on any assumption that a "particular" player may not swing or hold a racket in such a way so as to a more power to his groundstrokes by transfering more of his body wt.
His work depends on many assumptions and Avg player results.
The first quote shows a variance of .12 in RP or racket power, in the hands of the people he used in his control group.
That alone pretty documents the point of how some players can add more power to their shots by the ablility to transfer more of their mass.


from Rod Cross work in 2006 on raw power of rackets-

"The RP for a concrete slab is about 0.75, as specified by the rules of tennis. The RP for a hand-held racquet, when the ball impacts the middle of the strings, varies from about 0.31 to about 0.43."
OK, so seems there is nothing to indicate that some very special player couldn't be able to have a number in the .50 RP range.

from an older work-
"Further experimental studies would be
desirable to unravel the complications introduced
by the force of the player's hand on the handle, in
relation to the effect on the COP."

and

"The maximum possible ACOR of a racket is obtained when the
head is clamped, in which case there is no energy
transferred to rotation or translation of the racket
and the ACOR is then equal to the COR"

His big if here-
"If the total energy of the racket plus the arm remains
constant, "

the formula for groundstrokes he suggested is in the next paragraph, since that is what we are discussing with the backhand-

"It is also of interest to consider the effect of
additional mass on groundstrokes. If the ball is
incident normally at speed vin, then the speed of the
ball off the racket is given by v ˆ eAvin + (1 + eA)V.
Figure 11 shows an example where vin ˆ 78 km h)1,
x ˆ 30 rad s)1, A ˆ 0.2 m and where eA is given by
the experimental data in Fig. 9. It was assumed for
simplicity thatxis independent of swing weight. For
a groundstroke, this is a reasonable approximation
since (a) the player does not normally swing as fast as
possible and (b) the variation in swing weight is not
as signi®cant when the rotation axis is further from
the butt end of the handle."

[crass_lawner]

Airforce although there are some parts of your post that I am unable to or haven't taken the time to understand you have really hit upon some key points there. For example this quote from Rod Cross:

Further experimental studies would be desirable to unravel the complications introduced by the force of the player's hand on the handle, in relation to the effect on the COP.

At least at this point Mr. Cross is acknowledging that he hasn't taken the force of the player's hand on the handle into account (the COP is the "center of persussion"). I think that if he had taken the force of the player's hand into account, he would recognize that the following statement he made is untrue:

If a 100 lb male and a 200lb player both swing the same racquet at thesame speed and strike the ball at the same spot on the strings thenthe ball speed will be the same. Whoever swings the racquet thefastest will hit the ball the fastest. In fact a skinnyguy might be able to swing a racquet faster than a heavy guy because his arm is much lighter.

The following quote by Mr. Cross:

The maximum possible ACOR of a racket is obtained when the head is clamped, in which case there is no energy transferred to rotation or translation of the racket...

...pretty much proves my point if you understand what it's saying. Since ACOR is the measure of a racket's power, Cross is saying that a player with a vice grip is going to generate more power than a player with a limp grip. Notice there is no mention of racket speed or acceleration here, because he is assuming that those factors would be equal. Why is this?

It's because a vice grip absorbs more of the force that has been transferred from the ball to the racket. The difference between a tight grip and a limp grip is that the tight grip is exerting more force on the handle, which is exactly what the grip of a heavier person will do assuming the same grip tightness as a lighter person.

I'm not saying that a heavier person holds the racket tighter, or that holding the racket tighter is good (in fact in the modern game it's usually not), but merely saying that holding the racket tighter and having more weight behind your hand (as a heavier person does) have the same effect of exerting more force on the handle. And by Cross's own admission in the above quote, exerting more force on the handle maximizes the power (ACOR) of the racket.

Airforce you wrote the following quote from Cross:

If the total energy of the racket plus the arm remains
constant,

the formula for groundstrokes, since that is what we are
discussing with the backhand-

...which is also very telling if not a bit hard to read. I assume there was some formula written in there somewhere? The formula itself isn't that important but what's important is what he's basing his formula on, which as Airforce writes is a very big assumption. Cross is assuming that "the total energy of the racket plus the arm remains constant" which is a fine assumption to make if you are testing people of the same weight, but if not then the "weight" or more accurately "momentum" of the heavier person's racket will result in a more forceful groundstroke, something Cross failed to acknowledge in the second quote of his that I posted here.

I'll respond to sesjel's post later if I have time.

[airforce1]

the formula for groundstrokes, since that is what we are
discussing with the backhand-

It is also of interest to consider the effect of
additional mass on groundstrokes. If the ball is
incident normally at speed vin, then the speed of the
ball off the racket is given by v ˆ eAvin + (1 + eA)V.
Figure 11 shows an example where vin ˆ 78 km h)1,
x ˆ 30 rad s)1, A ˆ 0.2 m and where eA is given by
the experimental data in Fig. 9. It was assumed for
simplicity thatxis independent of swing weight. For
a groundstroke, this is a reasonable approximation
since (a) the player does not normally swing as fast as
possible and (b) the variation in swing weight is not
as signi®cant when the rotation axis is further from
the butt end of the handle.

thanks Crass,

I believe he is saying....

"then the speed of the
ball off the racket is given by v ˆ eAvin + (1 + eA)V"

is the formula to be used for the speed of a groundstroke. If I'm
understanding this correctly, this is different from the one mentioned
in previous posts for a serve.

He also seems to admit little or no work has been done on this aspect.

Is short, all of his works I read (4-5),
seem to admit that they take the player aspect out of it due to the myriad of variables involved, and focus entirely on the racket and how it behaves independent of a player.

For me, this statement by Cross...
"The RP for a hand-held racquet, when the ball impacts the middle of the strings, varies from about 0.31 to about 0.43".

makes it clear that an individual player can make a significant impact (excuse the pun), over and beyond what velocity he generates. And 0.31 to 0.43 was just the gap in his control subjects. Some particular pro player could possibly blow those numbers off the chart due to some quirk in his style and strength, AND that has been our point from the start.

[airforce1]

the formula for groundstrokes he suggested is in the next paragraph, since that is what we are discussing with the backhand-

"It is also of interest to consider the effect of
additional mass on groundstrokes. If the ball is
incident normally at speed vin, then the speed of the
ball off the racket is given by v ˆ eAvin + (1 + eA)V.
Figure 11 shows an example where vin ˆ 78 km h)1,
x ˆ 30 rad s)1, A ˆ 0.2 m and where eA is given by
the experimental data in Fig. 9. It was assumed for
simplicity thatxis independent of swing weight. For
a groundstroke, this is a reasonable approximation
since (a) the player does not normally swing as fast as
possible and (b) the variation in swing weight is not
as signi®cant when the rotation axis is further from
the butt end of the handle."

Sorry, but it's hard to present all this data without writing a book in the process and I was in a hurry this morn.

the first part of the above quote is where I pointed out that we are looking at backhands (and the formula for them) of Nalbandian, not the formula for the serve, which Cross says is different. The second part has the formula in there with some important info, such as reminding us that players often don't swing max vel on groundstrokes, which is significant.

[airforce1]

little more

We must remember that almost all of the work by Cross seems to be centered around serving power of a racket, and not what we are discussing, which is groundstroke power. Some may say "so what", but Cross says that is quite different due to several factors.

To illustrate my doubts on any given stand alone study, below I list 3 quotes from different studies or articles, all by the famous Rod Cross.
Each of these could be construed to have conflicting implications.

"There are other factors that influence racquet power,
such as the actual impact point on the strings,
the actual balance point and the swingweight,
but the weight of the racquet is the main factor."
or
"Any useful definition of racket power must
include both the ACOR and the swing
weight of the racket."
or
"Further studies
are also required to determine the relationship
between racket speed and swing weight so that the
concept of racket power can be more properly
assessed."

Well, which is it? Mostly these kind of statements where there to justify using a certain parameter or just choosing to leave it out or go with another in it's place.
Please don't get me wrong. I will still use and value reading his work (much like with BG on this site) and maintain great respect for what he has added to our sport. But that doesn't mean I won't question things that don't seem quite right to me. Most times these questions lead to me a better understanding, whether I'm right or wrong.

[crass_lawner]

Dominant arm is the one leading through the shot, and "hitting the ball"; one of the ways double hander is taught is (in case of right handers) to primarily learn to hit left-handed forehand. Annacone is not saying anything explicitly about distribution of the force met by the player in terms we are discussing here (other that referring to the right hand of the player in question as the dominant) - he is giving the help in terms of getting the feel for the swing and path of the racquet through the swing and "through the ball".
The player asking the question is having his right arm as dominant, clearly indicated by his grip with the right hand.
This is not always the case - many players have the other version, where left hand is dominant and leading through the shot.

It's simple really, if you're right handed, your right arm is your dominant arm, and if you're left handed your left arm is your dominant arm. Since the 2hbh is hit on the opposite side of the body as a person's dominant arm, the non-dominant arm becomes the primary force generator/absorber, and the other (dominant) arm is there mostly to guide and stabilize.

This is what I, Paul Annacone, and Mary Joe Fernandez are all saying, and what Caroline Wozniacki is doing. Obviously if you're hitting a shot like a left-handed forehand (as Annoacone suggests), your left hand/arm is going to be creating and absorbing the vast majority of force, so actually he is saying something explicitly about the distribution of force.

As for the rest of your post, it concerns things which have already been discussed ad naseum here, but I'll respond to some of it. Yes the kinetic energy of the racket is an important component of the force with which the racket meets the ball, but it's not the only component. There is also the force with which the hand/arm are is supporting the racket. This force is also composed of two forces: The kinetic energy of the hand and the momentum of the hand.

Since the hand has a great deal of body weight (due to the kinetic chain) behind it and not a great deal of velocity (compared to the racket head), I believe that the momentum of the hand/arm is the more significant of the two forces. And, since the majority of the player's body weight has been transferred to his arm/hand, this large number figures prominently in the (momentum = mass * velocity) equation used to determine the force it exerts upon the racket.

And airforce please forgive me if I don't dive into an analysis of the last portion of your post (the v ˆ eAvin + (1 + eA)V portion), but to tell you the truth I feel like I've pretty much sorted out what I wanted to sort out with regard to this topic and am a bit too burnt out to push on much further. But I totally agree with what you're saying in the rest of your post. The variations in racket power generated by different people and Rod's inability to identify the significance of swingweight are key points that detract from his view and support ours. This is a pretty key quote from him:

Further studies are also required to determine the relationship between racket speed and swing weight so that the concept of racket power can be more properly assessed.

At least he realizes what's missing, but he doesn't realize the implications of what's missing, namely the fact that a better understanding of swingweight would negate this claim that he made earlier:

If a 100 lb male and a 200lb player both swing the same racquet at thesame speed and strike the ball at the same spot on the strings thenthe ball speed will be the same. Whoever swings the racquet thefastest will hit the ball the fastest. In fact a skinnyguy might be able to swing a racquet faster than a heavy guy because his arm is much lighter.

Swingweight is very significant because it's a combination of momentum generated by the body and momentum generated by the racket. Although it was a recent trend to overemphasize racket momentum, it seems that some people are beginning to realize that it's the momentum generated by the overall system that is most significant. For example I found this quote by David Bone, TENNIS technical adviser and executive director of the United States Racquet Stringers Association:

Ideally everyone should be getting away from talking about weight and balance, and instead talking about one number, which is swingweight. If you know the swingweight of a racquet, you don’t need to know the length of the racquet, you don’t need to know the weight of the racquet, you don’t need to know the balance of the racquet. All of those get incorporated.

It was in this article: http://www.tennis.com/yourgame/gear/...aspx?id=164596. Of course you have to understand that bodyweight is a component of the amount of weight that one can put into one's swing in order to understand the full implications of Mr. Bone's statement, but that's something that we've already talked about quite a bit.

[airforce1]

Crass,
funny thing here is I'm not really convinced either way on this issue yet, and have tried to look at it with an open mind. My main aim is to support posters like you getting a fair say on an issue like this, and not being shut down by some study that may or may not address the issues at hand.
You have made some good points that I wanted to hear out.
I think we have made it pretty clear that much of the " expert comments/studies" are full of limiting assumptions and in some cases, just plain mis-applied.

My personal guess is that biggest factor of getting your wt towards the shot, adds control thru alignment, which in turn, allows you to cut loose with more of your power with confidence. This is keeping in mind that we all have swing speed in reserve on groundstrokes, that we can learn to apply as we have more control of our shots.

[crass_lawner]

O.K. airforce, sorry if I assumed more than I should have. I'm still confused about many aspects of this too, but there are some fundamental points that I'm pretty sure of. I'm sure that there are many inaccuracies in my posts, but I just see even more inaccuracies in some other people's posts. Maybe over time I'll be able to gain a clearer understanding of this issue.

[mntlblok]

One other point, you never see top players with two backhands, or at least two backhand drives, one with one hand and one with two. It's hard enough to have one.

When I've seen Andy Roddick on the practice courts, he's spent a good bit of time just fooling around, hitting left handed, etc. Saw him hitting a topspin one hander (right handed) and seriously wondered why he doesn't use that instead of his two hander. It was really impressive (to me).

Kevin