Serve toss question....

[gzhpcu]

Found the Rod Cross chapter on the internet here:

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

and here is Brody:
http://books.google.ch/books?id=iTad...ectory&f=false

[tennis_chiro]

Almost, but not quite

Don,
I feel we have gotten sidetracked on a purely theoretical point, as I have already said. We have seen the effect of gravity, drag and the magnus effect on the trajectory of the ball (the latter even causes the ball to swerve to the side, lengthening the distance between impact on the racket and hitting the service box).

In respect to your original question on tossing the ball far into the court:
- the distance to the receiver is reduced.
- the receiver has less time to react.
- the speed gained on the serve by the severe body lean (more body weight going into the serve) is minimal
- the impact on the biomechanics of the serve is (to me) unclear at this point
- the major advantage today is for doubles players wanting to get to the net fast

Would you agree?

Not quite. This is my question. Looking at how far out some of these servers actually are reaching into the court made me question the reduction in reaction time. In the old days, servers were reaching one or two feet and all the emphasis was on getting up. Now they are reaching into the court even though they don't go forward. Certainly, the receiver has less time to react and I think that may even be more benefit than the percentage of the total distance of the flight of the ball would indicate because the body doesn't move until the initial neural reflex processes the information; and by then the ball is halfway to the receiver.

So if there really is a benefit from reaching in that much, does it outweigh the reduced percentage of serves made due to the increased difficulty of this delivery? You have to weigh the gain in offensive effectiveness against the reduction in serves made. It is clear to me that for Isner and Karlovic, this is a no-brainer. But for someone 6' 1" tall or less, I am not so sure.

In the end the theoretical argument is just that, but it gives a better viewpoint from which to make the judgement call. I think it is beyond me at this point to fully numerically assess degree of difficulty of reaching forward (and all the leg thrusts etc. associated with that) vs any reduced consistency (just my guess) vs increased offensive effectiveness of the delivery.

I am just trying to get a starting point with the simple plane geometry models. My thought was that with a solid starting point there, we could guestimate (with some scientific input like the drag, etc. although I don't know how long it will take me to make sense of that paper on drag) the additional influences of spin and drag and, of course, gravity.

That is the general direction of my question here. So I don't think it is a totally bogus exercise in theoretical jibberish. I'm looking for a conclusion that influences whether I try to get my advanced players to emphasize getting forward as much as they can. Only when they are ready for that, of course.

don

[tennis_chiro]

Not a throwaway comment at all

Don,
I feel we have gotten sidetracked on a purely theoretical point, as I have already said. We have seen the effect of gravity, drag and the magnus effect on the trajectory of the ball (the latter even causes the ball to swerve to the side, lengthening the distance between impact on the racket and hitting the service box).

You make this comment kind of as an aside, but that is an important part of Sampras's serve's effectiveness. Certainly, it helped him get the ball in the court, but the spin made the ball "heavy" in more ways than one. It was difficult to read and time as the spin effected the bounce of the ball and it was also difficult to control as the spin effected the way the return came off the receiver's strings!

don

[tennis_chiro]

Wish I'd had this kind of material in Engineering school

Found the Rod Cross chapter on the internet here:

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

and here is Brody:
http://books.google.ch/books?id=iTad...ectory&f=false

Phil,
this is great stuff. But I actually have a job. Actually, a couple of them. But I will get through all this. It will just take me some time. I wish I'd had this kind of information to look at when I was going through engineering school 40 years ago. I would have been a lot more interested in my Dynamics of Elastic Systems and Fluid Dynamics classes. Might actually have become an engineer.

But I'm going to need some time.

don

[johnyandell]

Guys,

I won't pretend that I have followed this or even that I could have (or wanted to...?)

HOWEVER, I did dig back into that speed spin study of Sampras and Rusedski, and found the numbers on the net clearances that were actually measured.

The height of the contact for both was about 9' 6" Average clearances were:
Deuce Down the T 7"to 8"
Deuce Wide 5" to 9"
Ad Down the T 5"
Ad Wide 8" to 11"

Don't know if or how this may help but thought I'd throw it in.

[gzhpcu]

In the old days, servers were reaching one or two feet and all the emphasis was on getting up. Now they are reaching into the court even though they don't go forward.
.....
don

Don,
In the "old days" (I understand the days of Gonzalez and Hoad) they could not go "up", because they had to keep contact with the ground with one foot on impact. Gonzalez and Hoad both leaned into the court, 1-2feet.

Look at Federer:


Uploaded with ImageShack.us
He just jumps up and is up in the air on impact.

Compare with Sampras who is up in the air, but also well forward :

Who has the better serve? The better first serve percentage?

[gzhpcu]

Guys,

I won't pretend that I have followed this or even that I could have (or wanted to...?)

HOWEVER, I did dig back into that speed spin study of Sampras and Rusedski, and found the numbers on the net clearances that were actually measured.

The height of the contact for both was about 9' 6" Average clearances were:
Deuce Down the T 7"to 8"
Deuce Wide 5" to 9"
Ad Down the T 5"
Ad Wide 8" to 11"

Don't know if or how this may help but thought I'd throw it in.

Shows that the net clearance well over the 3" Don is using, because they have heavy spin.... Thanks, John

[johnyandell]

Exactly don't know if you guys can incorporate that into your discovery of the laws of the universe.

[gzhpcu]

It probably raises our level of confusion to greater height...

[tennis_chiro]

3" is the bottom of the range

Shows that the net clearance well over the 3" Don is using, because they have heavy spin.... Thanks, John

The 3" was meant to be the bottom of an acceptable range. The numbers John supplied show that Rusedski and Sampras's serves were right in the middle of the 16" acceptance window, about 8". This, in spite of the fact that both of them hit heavy first serves; Rusedski's was not quite as heavy, but he held the fast serve record for a while and was 6'4" tall.

I don't think Sampras's first serve percentage was that good. Anytime he got over 60% though, he was a prohibitive favorite because his percentage of points won on successful first serves was very high.

You don't have to go that far back to see more "classic" service motions. Even Becker and Lendl on this site are only one or two feet into the court. I think Sampras was the first really successful big server who threw himself into the court. It's also noteworthy that the picture of Hoad Phil posted at the beginning of this thread has Hoadie almost as far into the court as Sampras, but with one foot on the ground!

There are an awful lot of things I would try to copy from Sampras's serve, but I would not recommend copying the exact motion, not after seeing the overhead photos that were posted, I think, by Geoff Williams here recently. I've heard many people talk about Pete's "golden arm" and special gift he had there, but those pictures make me think it was more of a "golden core" as well as a "golden shoulder" that enabled him to do what he did for so long and so well. And he had that serve even when he was almost 20 pounds lighter in 1990!

I'm not saying the serve should be hit 3" over the net, but that is about the bottom limit of the range for a first serve, probably 3" to 14". But for serves as fast as Rusedski or Sampras, probably 10" or 11" is the max because they weren't hitting many serves short in the box. Remember, with a trajectory less than 7/8 inch above the net, you would be hitting a let serve.

I want to come back to what I said a couple of posts back:

"I am just trying to get a starting point with the simple plane geometry models. My thought was that with a solid starting point there, we could guestimate (with some scientific input like the drag, etc. although I don't know how long it will take me to make sense of that paper on drag) the additional influences of spin and drag and, of course, gravity.

That is the general direction of my question here. So I don't think it is a totally bogus exercise in theoretical jibberish. I'm looking for a conclusion that influences whether I try to get my advanced players to emphasize getting forward as much as they can. Only when they are ready for that, of course."

I still need to answer this question with something more than I can supply right now. Maybe I do need to write a "paper" as Julian suggests. In any case, I need to take a deeper look at some of the material I just picked up with the books from Plagenhoef, Brody and some of the papers from this thread and try to formulate my analysis a little more clearly. It will take me a while. Then I will come back to try and pick up this thread.

don

[gzhpcu]

Good luck Don... Get it peer reviewed by us and maybe John will put it up on the site....

[gzhpcu]

P.S. Vic Braden answered someone's question on why they couldn't serve fast this way:

"That's normally due to two factors. First, your palm opens up to early on the forward movement and you end up pushing your racket. The bigger issue is that your upper arm (the link from your shoulder to your elbow) needs to be moving 180 degrees forwards before impacting the ball. That means you will have to toss the much further out in front to achieve that goal. The hardest hitter in pro tennis strike the ball four to five feet into the court when striking the ball."
This quote is from an iPhone app "Vic Braden's Tennis Tips"...
in the video, he says you have to lead with the elbow on the swing. Something I don't agree with...

[julian1]

Couple remarks and questions about chapter 42 of Rod Cross

Don ,
I have some problems with reading/understanding of Rod Cross.
It is very slow reading for me.

1.I assume that v in equation 43.a1 of Rod Cross has the following meaning/definition

v=sqrt( vx*vx+vy*vy )


where sqrt stands for a square root of ....

If I am correct the right hand side of Eq.(43.a1) depends on sqrt(vx *vx+v y*vy) multiplied by vx


It looks like a very complicated behaviour/dependendence because the right hand side depends on BOTH component of a speed vector v

Nothing deep in a sentence above but it will get a bit more complex.As you see I have some problems with editing/putting indices
at correct levels/positions in my PC editor.


2.I understand that Eq.(42.a3) is obtained from Eq.(43.a2)
Please note that note that Rod Cross dropped an index vx in Eq.(42.a3)



3.A sentence "initial speed = 15 m/s downwards.... at speed v=21.006 m/s "
Is he saying that a speed at the END is HIGHER than a speed at the VERY BEGINNING?

4.Do you understand why theta disappears from Eq.(43.a1) and (43.a2) ?

[gzhpcu]

Don ,
I have some problems with reading/understanding of Rod Cross.
It is very slow reading for me.

1.I assume that v in equation 43.a1 of Rod Cross has the following meaning/definition

v=sqrt( vx*vx+vy *vy )


where sqrt stands for a square root of ....

yes

If I am correct the right hand side of Eq.(43.a1) depends on sqrt(vx * vx+v y*vy) multiplied by vx

Correct

2.I understand that Eq.(42.a3) is obtained from Eq.(43.a2)
Please note that note that Rod Cross dropped an index vx in Eq.(42.a3)

Yes, because motion is only along the y axis for a vertical drop.

3.A sentence "initial speed = 15 m/s downwards.... at speed v=21.006 m/s "
Is he saying that a speed at the END is HIGHER than a speed at the VERY BEGINNING?

Yes because the ball is dropping downwards.

4.Do you understand why theta disappears from Eq.(43.a1) and (43.a2) ?

Because Vx = V cos(theta), Vy = V sin(theta) have been substituted in the equations.