Interactive Forum: September 2014: The Egg at 11000 Frames Per Second

[johnyandell]

The Egg at 11000 Frames Per Second

The tennis ball is round, correct? Many observers know it flattens out and imbeds on the string bed. But what happens as it leaves the string bed? The answer may surprise and fascinate now. Check out this Rafa Nadal serve from the practice courts at Indian Wells filmed at more than 11,000 frames per second. Surprised by what you see?

[johnyandell]

Quicktime version

The Egg at 11000 Frames Per Second

[gzhpcu]

Interesting how the ball seems to oscilate after leaving the racket.

The racket is practically perpendicular at impact, then starts moving downward as the ball rebounds.

Great footage.

[stotty]

The only other guy who could possibly do that to a ball is probably Geoff Williams.

[khaled01]

Speaker at the ITF worldwide conferences

Interestingly enough the racket didn't bend at all during impact like what happens to some of my players in 100 frame/sec clips. Is this due to Nadal using a super stiff racket and hitting the ball in the sweet spot comparing to softer rackets and off center contact point by all other mortal players. Although they are using the same brand and model of Nadal's racket ;also I have seen the bending of the racket backwards during first serves in some in other models.

[johnyandell]

Good question! In the regular stroke archive you see some racket bending but that's an artifact from the codec in some of the cameras. Have you got a url of a clip from the high speed archive that shows this?

[klacr]

Very cool video John. Who knew the ball did this! Then again, does the ball react like this for everyone? Do you have video from other players at this speed? Is there a certain speed or terminal velocity the racquet needs to be traveling to produce this egg shape on the ball. Is it a mix of speed and spin and what is that ratio? So many questions this short clip brings up. Such a Tease.

Kyle LaCroix USPTA
Boca Raton

[khaled01]

Good question! In the regular stroke archive you see some racket bending but that's an artifact from the codec in some of the cameras. Have you got a url of a clip from the high speed archive that shows this?

Thanks for the info I think it is an artifact because it only happened when I am using the slow motion iphone app which is why I don't have a url of the clip

[johnyandell]

Kyle,
I do think it happens in pro tennis all the time. Great questions....what speed what strokes what spins? Just a small peak into the invisible world. It's like the bottom of the ocean, 5% explored...

[johnyandell]

Khale,

We found that to be the case in a couple of the cameras we used in the middle stretch of building up that amazing archive...(only 65,000 strokes...)

[giancarlo]

Interestingly enough the racket didn't bend at all during impact like what happens to some of my players in 100 frame/sec clips. Is this due to Nadal using a super stiff racket and hitting the ball in the sweet spot comparing to softer rackets and off center contact point by all other mortal players. Although they are using the same brand and model of Nadal's racket ;also I have seen the bending of the racket backwards during first serves in some in other models.

From all the videos I have edited for the archive, the bending of the racket is most noticable for Federer (before the switch to new racket) and Berdych. Since Djokovic switched to his new racket a few years back, there is almost no bending at all for the serve or ground strokes (same is true for Nadal).

What's interesting, is that Federer's new racket also no longer bends like the old one, which explains the extra pop on the serve on easy power.

[shiuey]

Flat serve?

Great video. I was curious, was this a flat serve? Does the ball do this with every type of spin and how does the changing shape of the ball affect it's trajectory?

[johnyandell]

S,
Good questions. The answer is we think there is this type of deformation on all high velocitity serves and other shots as well. There really is no such thing as a truly flat serve in pro tennis, but one of the questions is does the shape change with the type and amount? Maybe we will be able to do additional filming in the future to answer some of these questions. But one point is clear: tennis has invisible dimensions...

[klacr]

tennis has invisible dimensions for sure. The rabbit hole runs deeper than many of us will ever realize.

Other question to add to the laundry list of queries this short clip has produced.
- How much of an impact does the string have on creating the egg shape? Full poly to a syn gut? Probably a question for Geoff.

- The amount or minimum of racquet head speed and rpm's needed to create this? Will need a larger sample size for this probably.

- Atmospheric conditions that could aid in this effect? Video was shot in Indian Wells, in dry desert air in altitude. Would egg shape be as pronounced in more humid conditions, at sea level?

Not sure if any of these can be answered but always good to put them out there and maybe I'll learn something new.

Kyle LaCroix USPTA
Boca Raton