where'd the bent arm come from anyway?

[oliensis]

Rosooki,
Well described, thanks. That's roughly what I was trying to get at when I mentioned in some of my earlier posts that the double bend created a more complicated series of fulcrums that might create more acceleration!

But your physics description was much better than mine.
Bravo.

[uspta146749877]

Application to serve

Sorry to be late to the party, but I just found this thread. I guess it falls to me to be the physics police.

It has been stated here that it requires less force to hit the straight arm forehand. That's simply untrue from a mechanics point of view. The longer the lever, the more force that must be used to swing it. A simple balance where a weight is balanced on one end shows how this works. A given amount of force on one end will raise the weight on the other end. The longer you make the end where the weight is, the more force must be applied to raise it. When swinging a tennis racket, and you want to accelerate the racket, it will take more force to accelerate a racket at the end of a longer arm than at the end of a shorter one. Imagine a children's merry-go-round at a park that you have to push to get going. The longer the radius of the merry-go-round the harder it is to accelerate it to a given speed.

The second issue is racket head speed. If you swing a stiff rod (an extended arm) at a given rate that is the velocity you will get. All points of a rigid body have the same angular speed. Points with a greater radius have a greater linear speed, and that's the benefit straight-armers are referring to - the end of the racket will be traveling faster. Now if you put a joint in the middle of it so that the joint can swing freely, and swing it again, but block the swing mid-swing, below the joint, so that one part stops and the remainder of the rod continues to swing, what happens to the angular velocity of the section still swinging? Ask a tetherball player (remember that fun game?) or a figure skater. Angular momentum makes it speed up. And another point of rotation is added. The bent-armer who uses his arm/shoulder/chest muscles as well as body rotation to pull the racket across his body has two engines, two short rotational points working together, and a lot less force required on each.

One side issue with this is that if you have already spent the energy to accelerate a straight arm, shortening the length of the arm mid-swing should make the arm really speed up with the same energy expenditure involved. If you start with a straighter arm in the backswing and shorten it through the swing the acceleration will be appreciable. I think that is a significant advantage to a bent-armer as well as to a baseball batter. Instinctively, hitters pull their arms into their chest when really trying hard to accelerate the bat.

A last remark can be applied to serve-
for example to a stage between a maximal upward stretch and a contact point

julian mielniczuk
usptapro 27873
Courtside Tennis Club,Bedford,NA

https://www.julianmielniczuk.usptapro.com

http://www.ndatyngsboro.org/page.cfm?p=271

juliantennis@comcast.net

[bottle]

Faulty Assumption?

The discussion of physics is good, but I think the writer may be assuming that the arm swats through the ball like too many double-benders. I see the energy running straight out the tangent through deceleration-acceleration. At the same time, though, he is right that a lot of energy, more energy is needed to move a long lever through the ball than a short one, and that comes from the huge spiraling body leap. It applies great weight on the ball. These shots go fast and heavy whether it's Federer, Del Potro or even me or my present student, who is really beautiful, and she speaks seven languages, is half Czech, half Swiss. (I pick my students very carefully.)

She and I, naturally, have been doing the demonstration of relative arm strength where the student pushes on the instructor's hand first with a straight arm and then with a bent one. No contest at all. But energy running out the tangent is a totally different concept. I won't say it's a right cross or a right jab because I think there's light quickness more than power in the way the passive forearm and wrist undo the Mondo when hand rejoins original body orbit at original body speed. Just bowled racket head unfurls to the right. One can mime this with no body rotation at all.

Similarly, one can mime the smooth body rotation with no mondo or unfurling
and even hit nice mediocre shots and put the two elements together later.
Yes, the long, weak lever (the speed lever, the longer part with Archimedes
hanging on the end) can't compare with bent arm architecture so superior
for a big push. But I don't care at all whether some cellar door stays stuck or not. That sounds like work, not play, and my interest is in winning in tennis. Now, how can I put this? "A rolling stone gathers no moss?" How about, "The arm is stronger than it otherwise would be since energy is running out through it and the racket tip is tracking toward the right fence?" In any case, arm goes one direction, body another, and most human arms are strong enough to bear the strain the smoothly whirling body puts on them so long as they don't try anything foolish.

I do think smoothness of body whirl is essential to this enterprise. That's why I jeer at discussions of kinetic chain in this kind of shot (Should I apologize for being so opinionated? Maybe. I must admit some people might get interesting results if they fired hips marginally before shoulders, but I may not be at that stage right now, may never be, am more interested in precision since I already seem to have as much power as I want.) Arm applies the spin, body the weight. Steady smoothness of body is best and most adjustable, I think. I'm putting the Zen of the thing on accelerating the arm along a tangent while keeping body at constant speed to take racket through the ball.

[bottle]

Egads, anabelleEnads, I'm not even sure how much of what I wrote 14 years ago I still believe or have ever fully comprehended, e.g., Brian Gordon has disabused me of the notion that deceleration-acceleration is something valid to think about for a person with gonads when it comes to tennis strokes. But Peter Burwash did point out long ago that if you have a bent arm you can then make last instant adjustment in two different directions, i.e., squunch arm still more if crowded and make it longer to reach a wide ball. Of course, the tennis establishment would prefer that all such precision come from arrangement of thy feet. Brent Abel has advised that I think less about mechanics and more about strategy. He likes to serve right at the bottle to screw up his lugubrious stroking thoughts. Lastly, I warn against law school unless you plan on earning a loot.

[bottle]

Hmmm, annabelleEnads is gone. But before she disappeared, she brought back a whole, long, fabulously interesting thread for anyone like me who likes stroke technique on its own recognizance (whatever that means). Thinking about it may very well make you a worse player. That seems the consensus. But forget that! The further back you go in this thread the more interesting you should find it to be. (Also, what does the consensus know, ever, other than that Trump is an idiot.)