Interactive Forum August 2012: The Invisible Collision

[johnyandell]

The Invisible Collision

What does the interaction between a tennis ball and the copoly strings that dominate pro tennis actually look like on a high velocity forehand? Here is another Tennisplayer first. Two views of huge forehands hit by our contributing editor Peter McCraw, filmed at 4000 frames a second using a new camera technology available exclusively to Tennisplayer.

Although you can see a lot in the animations, stepping through frame by frame in the Quick Time movies is highly recommended. Watch from the rear view how the strings slide down and then "snap back," a phenomenon first described on Tennisplayer article by Josh Speckman (Click Here.) Now check out the depth of the penetration of the string bed by the ball on the side view--and the oscillations in the ball's shape after it leaves the string bed. Crazy! Your thoughts please!

Peter, by the way, is an Australian high performance coach who is also involved in the development of a new generation of copoly that increases the current spin effects by yet another increment. Those are his new strings in the racket. Stay tuned for more on their progress on the tour and their availability in the commercial market!

[johnyandell]

Quicktime version

[stotty]

Now that is bloody amazing! I can't believe the distortion to the ball at impact, let alone the depth of the ball pocket. That really is amazing.

[vrc10s]

Spin

Amazing video!

On the side view you can see the ball spinning on the way in but the label hardly moves as the ball is leaving the racquet. The swing looks like it should have topspin. Are we just not seeing the ball long enough?

Great work as usual, John!

[vrc10s]

spin

I watched the video several more times on a bigger screen and you can see some spin, just not as much as I expected considering the swing angle.

[tennis_chiro]

More spin than you think

Amazing video!

On the side view you can see the ball spinning on the way in but the label hardly moves as the ball is leaving the racquet. The swing looks like it should have topspin. Are we just not seeing the ball long enough?

Great work as usual, John!

I'm just using the click action on the browser and it seems to move the clip one frame every 4 clicks. It took about 36 frames to move the label a quarter turn. That's one revolution per 144 frames. 4000 fps works out to almost 28 revolutions per second and 1666 RPM. Pretty good for a teaching pro forehand, even a high performance one!

It seems the ball doesn't slide at all on these strings!

don

[don_budge]

Sliding Strings...

...and I like the way the strings slide as the ball imbeds itself into the string bed.

[TimX]

Hmm, those look suspiciously like Rod's Flex Infinity CP+ in the 1.30...

[holzi]

Am I wrong or isn`t the racket slightly closed at impact. All my teaching carrier I`ve been telling my students that the racketface should be neutral when hitting a shot from baseline to baseline. John what´s your idea on that?

[julian1]

Three different stages

Am I wrong or isn`t the racket slightly closed at impact. All my teaching carrier I`ve been telling my students that the racketface should be neutral when hitting a shot from baseline to baseline. John what´s your idea on that?

A racketface can be SLIGHTLY closed at ALL three stages-
before the contact
during the contact
after the contact

[jimlosaltos]

Ball slides -- 2 inches? Milliseconds

Amazing. Looks like the ball slides down the racket face about 4 grommets, maybe 2 inches. If I remember, Crossley wrote about the ball sliding 4 inches on some serves.

How many milliseconds is the ball on the strings? I'm guessing I clicked through 75 frames, but since some don't show motion I'm not sure. Is that 18 milliseconds dwell time? 4000 fps = 4 frames / millisecond. 75 frames/4 ms = 18.75? Hate doing math in a comment window <g>.

Thanks for sharing

Just FYI -- At the risk of exposing my ignorance, I couldn't see the Quicktime version, but it showed up in the Preview of this post. Using Safari 6 in Mt. Lion. No problem for me, just saying. Nothing less compatible with Apple video than Apple software <g>.

[julian1]

Do you mean Cross?

Amazing. Looks like the ball slides down the racket face about 4 grommets, maybe 2 inches. If I remember, Crossley wrote about the ball sliding 4 inches on some serves.

How many milliseconds is the ball on the strings? I'm guessing I clicked through 75 frames, but since some don't show motion I'm not sure. Is that 18 milliseconds dwell time? 4000 fps = 4 frames / millisecond. 75 frames/4 ms = 18.75? Hate doing math in a comment window <g>.

Thanks for sharing

Just FYI -- At the risk of exposing my ignorance, I couldn't see the Quicktime version, but it showed up in the Preview of this post. Using Safari 6 in Mt. Lion. No problem for me, just saying. Nothing less compatible with Apple video than Apple software <g>.

Do you mean Cross?

[stumphges]

Am I wrong or isn`t the racket slightly closed at impact. All my teaching carrier I`ve been telling my students that the racketface should be neutral when hitting a shot from baseline to baseline. John what´s your idea on that?

The racquet face on a topspin shot is often slightly "closed" at impact, especially if the incoming shot has a lot of topspin and/or is hit on the rise. Both conditions result in high launch angles that can be countered by closing the racquet face, which a) lowers the launch angle and shot trajectory, and b) produces more spin, which will help the ball dip down inside the baseline.

Great videos! Thanks to John and Peter!

[johnyandell]

4 milliseconds on the contact and no the ball is not sliding nearly that much in my view--look at the pocketing on the side view--the strings are sliding--this is the snap back effect...

On the Apple thing Firefox will solves the problem.

[TMMTennis]

Flex Infinity

Hmm, those look suspiciously like Rod's Flex Infinity CP+ in the 1.30...

In fact they are Flex Infinity strings 1.25 White. You can find out more at www.flexinfinity.com.au. Be sure to check out the additional info about each strings performance by clicking on the pic of string. Very interesting reading - give comparison of dynamic tension (most important), tension loss and energy return. There are graphs also showing comparison.