February 15, 2013

F=MA?

[NOTE - See comments below by physicist Dave Bernstein. Since some of my physics wasn't quite right - though my conclusions were correct - I've deleted much of this blog, including the references to F=MA, which don't really apply here.] I'm not a physicist, although I do have a bachelor's in math from way back (Univ. of Maryland, 1986). But the physics of creating a powerful shot in table tennis, especially a loop, are seemingly right out of basic physics. (Any physicists reading this, feel free to elaborate, correct, or explain any of this. I know this more from a coaching point of view.)

When players loop, they often try to muscle the ball, resulting in using only a few muscles instead of timing them all together. To get mass behind your shot, you have to put your body weight into the shot. You can't do this with the upper body alone. It comes by rotating the body into the shot, almost with a rocking motion, starting with the legs and moving upward as each part of your body uncoils into the shot. You need the legs to get the hips to rotate, and you need the hips to get the rest of the body to rotate into the shot. Many players do not get this lower body rotation - especially the hip rotation - and so most of their body weight does not rotate into the shot. 

To get maximum velocity, you have to smoothly accelerate your body's mass into the shot. Watch the best players, and you'll see how they effortlessly generate power. They do this because they accelerate their body into the shot. This goes together with getting the mass behind the shot - it's the smooth acceleration of the body's mass into the shot, starting with the legs and then the hips, that gives such effortless power. 

It's not quite this simple. With sponge rubber, even without acceleration the ball sinks into the sponge and is catapulted out. This is true even with a plain wood bat, which also bends and then catapults a ball out. Around here is where I would love to have a physicist chime in.

If you want natural power in table tennis (especially when looping), focus on smoothly accelerating your body weight into the ball, focusing on the hip rotation, to maximize velocity at contact. Watch top players as they loop and see how they do this. When done properly you get great power with ease, and so, as I like to demonstrate for students and in clinics, you should be able to loop at seemingly full power while carrying on a conversation.

The above should also apply to smashing. However, since the contact with the ball is quicker on a smash - as opposed to a loop, where the ball sinks into the sponge at an angle and stays in contact much longer - I think the power transfer is much quicker, and so you can get great power without using the full body weight, though that helps. I know I can smash extremely fast with minimal body rotation and a powerful arm snap (from the forearm), but this doesn't work for looping.

Pings and Pongs

I've written so much recently about Table Tennis Tactics for Thinkers (Buy it! Now!) that it's been a while since I've mentioned that "Pings and Pongs: The Best Science Fiction & Fantasy of Larry Hodges" is also sold on Amazon. These are the 30 best short stories I've sold (out of 65), compiled in one volume. One of the stories is a table tennis fantasy, and table tennis shows up in passing in other stories. $15.95 or $9.99 for Kindle. (Buy it! Now!)

Here's a short description of "Ping-Pong Ambition," the table tennis story: "A table tennis player gets stuck in a ping-pong ball for 10,000 years, where he studies to be a genie - only to discover a surprising truth. Originally published in Sporty Spec: Games of the Fantastic Anthology, 2007."

What, you didn't know that outside table tennis I write science fiction & fantasy? Here's my SF&F page. C'mon people, sales of the Tactics book is way outpacing sales of Pings and Pongs, leading to some hard feelings between the two. Here's your chance to get in a little F&SF between your TT reading!

Update - Tim Boggan's History of U.S. Table Tennis, Vol. 13

We did three more chapters yesterday, bringing totals to 26 chapters and 409 pages. I've now cleaned up, placed, and captioned 826 graphics. The book is now projected to be 29 chapters and 456 pages, with 918 graphics. Chapter 26 ended with narratives of Americans in Europe, including Eric & Scott Boggan, Mike Bush, Brian Masters, Charles Butler, and Kasia Dawidowicz, as well as tributes to first ITTF president Ivor Montagu, who had just died. (This is 1985.) We should finish all 29 chapters tomorrow. Then, over the weekend while I'm off coaching all day, Tim will proof all the pages. On Monday we input the corrections. It's going to be a looong Monday.

I've also updated his web page and created the ad and flyer for the book. However, neither will go public until the book is complete. It should go to the printer on Monday or Tuesday, and copies should be available a couple weeks later.

Update - Table Tennis Tactics for Thinkers

Now it's on sale at Barnes and Noble, as well as Amazon. Complicating factor - both are selling it for $11.45 instead of the retail price of $17.95. I don't think table tennis dealers can match that price. I'll look into this next week.

USA Team Trials

Here's the ITTF article on the USA Team Trials held last weekend, focusing on the top finishers, Timothy Wang and Lily Zhang.

Women in Table Tennis

Here's a gallery of table tennis women.

Corrugated Table Tennis

This'll have some weird bounces!

What's on Your Mind?

One is on love, the other on ping-pong. And guess what is in the heart of this person?

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david.bernstein Sat, 02/16/2013 - 00:37

Hi Larry, I'm a physicist and I've had many conversations (and some arguments) over this issue with non-physicist table tennis players over the years.  The physics of inelastic collisions is more appropriate for analyzing this than Newton's second law.  When you think about it in terms of a collision there are really only two things that matter when ball meets bat: the first is the racket speed and the second is the energy lost in the deformation of the racket material.  Since the ball mass is so small compared to what it's being hit with it doesn't really matter (in terms of change of the ball momentum) what the ball is doing.

So strong shots mean maximum racket speed and using a racket material (blade and rubber) with small energy losses due to deformation.  How you generate a high racket speed is another matter, which you discuss very well, but it has nothing to do with the mass of your body or arm or racket or the time of collision (dwell) or the acceleration of the racket at the time of collision.  Table tennis rackets are light and it doesn't take much force to accelerate them.  This is why a 68 lb kid can hit a monster forehand.  The opposite is also true: once a racket is going fast it doesn't take much to deccelerate it. Hence the hard part of getting power into the ball is the timing.  You have to time all the components of your body so that racket meets ball at the moment of maximum racket speed.  This is the tricky part that takes years of training and it also explains why good players make it look so easy: they can intuitively time the impact exactly so that the racket is at its maximum velocity for a very short period of time during which the ball is struck.  So the reason why using your legs, trunk, hips, etc., works in creating power is mainly that it helps your timing.  I've seen very big strong guys get over powered by kids with limbs like pencils because the kids intuitively understand how to coordinate their pencils to get a maximum velocity at impact and the big guy doesn't (yet!).

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Larry Hodges Sat, 02/16/2013 - 01:06

Hi David, thanks for commenting on this. Sounds like my conclusions were basically right, but for the wrong reasons. As I noted, I know it more from a coaching point of view, and it is the inability to use the legs and (even more) the hip rotation that costs players power - or, as you put it, coordinating it with the rest of the body. Players who cannot generate good power when looping usually are trying to muscle the ball with their upper body, and so while I got the F=MA thing wrong, it means they aren't getting the velocity needed for power because they aren't using the lower body to generate the acceleration needed to get high velocity. Sound right?

david.bernstein Wed, 02/20/2013 - 07:07

I think so.  It seems to me that there are two important things going on: generating high racket speed and timing the impact for the moment of maximum speed.  Both are crucial and the theory suggests that using all the muscles in your body in the stroke helps generate the highest maximum velocity as long as you coordinate the movements correctly to translate all that power into your racket at exactly the right moment.  My guess is that using your legs and trunk helps in both respects.  You get more power from more muscle and the necessity to coordinate all those moving parts help you time the impact better.  The first is physical, the second psychological.  The big guy with all the muscle is probably generating a pretty high racket speed but doesn't get any speed on the ball because he's not timing it right, i.e., he's hitting the ball some time before or after its maximum speed.  This is not hard to do considering even a basement player can move their racket such that the velocity changes from zero to 70-80 miles per hour and then back to zero, in maybe one second.  Where in that one second does the racket hit its maximum velocity?  That period may be only tens of milliseconds long and thinking about that makes you see how critical the timing is.