Suspended Ball Movement After Service Contact?

[doctorhl]

John, I finally viewed one of your incredible super high videos that confirmed my observations of a seemingly brief period of suspended ball movement after contact on certain serves. The rate of movement of the ball immediately after contact looks almost zero in your video, then speeds up in a steep angle of descent ......maybe descending quickly down to the T on this ad court view.

High Speed Videos Archive
Ball Racket Interactions
Serve
Roger Federer 2ndS Arm Action Rear 10000fps

I visually compared the arm path and racket face angle, ball compression, and rate of ball movement after contact with:
Roger Federer 1stS Arm Action Rear 10000fps

The slight differences in variables between these two serves, while maintaining racket head speed , seem to account for that "late breaking curve" the pros get without losing much ball speed.

[jimlosaltos]

Amazing, huh? And some great video in the archives, indeed.

As the strings stretch, they're going to move backwards, relatively to the frame, all while the ball compresses. i think John's mentioned somewhere in the vast archives how long the ball stays on the strings 0.5 millisecond, perhaps? Complete guess.

Somebody must have calculated the racket speed and when the ball stands still, and dwell time - but what a mess that would be: Elasticity of the ball, elasticity of the strings, deceleration of the racket head on impact.

Just for your interest, here's a still where that appears to happen, although I suspect the still spot of the ball is simply caught before impact. Shutter speed is 1/80th of a second. You can also see the ball blur as it takes off, moving faster than the racket head.

A tennis ball in flight is more like a blob of wax in a lava lamp than a billiard ball on a pool table, particularly as it first leaves the racket.

There are videos of tennis balls after impact where the back of the ball is actually moving backwards. A longitudinal, compressoin wave, like a slinky, moves forward, hits the front of the tennis ball and bounces back, stretching the back of the ball in the opposite direction from where it is going. Bounces again, reversing direction and stretching the front of the ball. All while it is also spinning. I think John/ TPN has one such video with a forehand.

My head hurts <g>

Caption: Johanna Konta at Bank of the West/ Stanford Taube WTA, 2016. (c)jf

filedata/fetch?id=101538&d=1689271695&type=thumb

[johnyandell]

Doctor,
I don't see that myself in the clips. Is that even possible according to laws of physics...(I got a B in high school physics...) Personally I see the compression of the ball on the strings for a couple or few high speed frames and as it comes off the ball takes off. Your spin hypothesis is interesting. Someone who undertands curve balls in baseball might be able to comment, but that's not me.

[doctorhl]

I just looked at the writing on the wall behind the toss in that Fed clip and noticed that the ball was hardly moving, but spinning on the first dozen(?) or so frames... need a frame counter! I don't know the physics either. My observation of " quick curve breaking" serves is that the ball appears to move slowly as it comes toward you( suspended), then quickly curves,.All I know is that kind of quick breaking curve is hard to track and not time the contact too early, as returners often fail to step in, as well as forward to adjust for the break Jim, I have noticed the lava lamp ball, particularly when we played with balls heavy with humidity! Help, my friends question my sanity.

[doctorhl]

This topic may have something to do with pitch tunneling. Tunneling is a concept that repeatability in delivery components is what fools the striker, no so much the ball path. If applicable, this might explain some of Fed's serve success since he was a master of repeatability....extremely difficult to read his serve delivery!

https://tht.fangraphs.com/pitch-tunneling-is-it-real-and-how-do-pitchers-actually-pitch/

[doctorhl]

John, Jim, does tennis have available software similar to StatCast 3d for baseball. Viewing cataloged 3d flight paths of a player's pitches than can be viewed from either the pitcher or batter's view is pretty neat. Just move the image with your finger to get a 360 degree view of comparative flight paths.

https://baseballsavant.mlb.com/visuals/pitch3d?player_id=477132#v=1&mainView=tracking&pov=umpire&hitterSide=all&marks=none&plays1=all&plays2=all&pitchColors=pitch_type&dualActive=false&summaryViewActive=false

[johnyandell]

Not that I know of.

[jimlosaltos]

Way out of my sphere. But ...

StatCast, as I understand it, is a far more sophisticated version of Hawkeye. Used to use Doppler radar, but now use multiple Hawkeye cameras to "stereocast" every player.

More cameras and way more expensive than tennis Hawkeye, but mandated in every ball park.

In Tennis, thinking out loud, Dart Fish is all that comes to mind. And that's not close. But it can now do overlays of pitches to compare motions.

https://www.dartfish.com/mobile

Tangentially, not what you're referring to, Rapsodo is a system I've read about but never seen that is used in baseball measures ball spin components. Let's see if I can find a link:

baseball pitching gurus talk a lot about gyro spin instead of just being sidespin or topspin. There's a device they use to measure it in real time called a Rapsodo.

https://rapsodo.com/pages/baseball

But I fear late at night I'm digressing again <g>

[doctorhl]

Information overload may make us all live to regret technology in sports.

[jimlosaltos]

Information overload may make us all live to regret technology in sports.

Hah! Quite possibly.

How to strike the perfect balance?

Watching Wimbledon I often found a network logo covering the serve speed read out. TV producers have dumbed down coverage so much to get the "non-tennis, general interest fan" it seems as if we're supposed to be grateful if they let us see the score.

At the other end of the spectrum, baseball showed off its Statcast. There's a squirrel that regularly runs across the field at one stadium. TV zoomed in on the squirrel and showed not just the speed at which it was running but the squirrel's current, peak speed, and average speed. Seriously.

Surely there must be a middle ground between having to rewind to find out what the score is, and knowing a squirrel's speed <g> ?

But here is a set of stats that changed baseball, a sport that has been around at least since 1837. Balls hit at a "launch angle" of 15-36 deg and an exit velocity of at least 100 MPH will be home runs in every park. After decades of teaching batters to hit flat or actually down on the ball (Rod Carew school of hitting), they now swing to match the math. Similarly, NBA games / tactics/ player drafts have been completely changed by quants concluding that a 2 point jumper is a wasted shot - either step back for a 3 point shot or go to the rim.

I wonder what we're missing in tennis for lack of this analysis?

Shohei Ohtani, a player that is redefining baseball, hit a home run 454 ft, by hitting the ball at an exit velocity of 115.4 MPH, at a launch angle of 28 deg.

filedata/fetch?id=101553&d=1689442222&type=thumb

[doctorhl]

Yes, serve exit velocity, velocity at bounce and velocity at opponent racket contact would be interesting data points. One could see the effect of court surface and spin rate on velocity.

[johnyandell]

Check the heavy ball section on Sampras and Rusedski that answers those questions.

[doctorhl]

Check the heavy ball section on Sampras and Rusedski that answers those questions.

Perfect. I forgot about that data... ahead of its time.

[arturohernandez]

Perfect. I forgot about that data... ahead of its time.

johnyandell Could we think of serving more like flinging the ball rather than striking it? For the longest time I thought about all my strokes in that way. Certainly, the stiff new strings also give that feel. But I have been experimenting with gut for two years and just find it too springy to control. And yet the feel I get is different. Rather than strike the ball it is as if I was catching it and throwing it rather than striking it.

It seems that the late breaking serve would use this catch and fling idea to its max. Since the fling happens only on contact, it makes it hard to read.

Just a thought about how to make all these stats into some kind of digestible concept that I could actually implement in a stroke.

[johnyandell]

Fling away... just make sure you continue the rotation of the hand and arm through contact and out to extension as in my current article