Interactive Forum April 2015: Gulbis Poly String

[johnyandell]

Gulbis Poly String

We've studied the ball interacting with poly string on a forehand before--but not an actual top 20 player hitting a huge forehand. What exactly happens in that invisible event when the ball is on the strings? Well here is what happens when Ernests Gulbis hits his forehand.

It's the best imagery yet of how poly works--shot this time at over 10,000 frames per second. And it's still not easy to see!

Some of the vociferous posters on the Tennis Warehouse message boards have been claiming the ball "rolls" down the string (they claim they can see this watching youtube video...). Uh, no.

But what really happens is hard to see even in the animation which is more than 30 times slower than real time.

So take the time to go frame by frame in the Quick Time version if you want to see the invisible.

Watch how quickly the incoming spin stops. Instead of rolling down the face, the ball pockets itself deeply in the string bed and flattens it's shape dramatically. Now watch the "snap back" as the poly strings kick the ball off the string bed...woah...what do you think?

[johnyandell]

Quicktime

Gulbis Poly String

[klacr]

Wow! Technology is a marvelous thing.
Gulbis actually hits this ball closer to bottom of the frame than the top of it. Also, his grip does not appear to be as extrme as I thought it would be.

What is also pretty cool as that much like the Nadal serve clip a few months back, this ball seems to pulsate as it leaves the string bed. Thanks for this clip John.

Kyle LaCroix USPTA
Boca Raton

[don_budge]

The Grip…the V and the Bevel. It's Western!

Also, his grip does not appear to be as extrme as I thought it would be.

Kyle LaCroix USPTA
Boca Raton

Geez…how much further can his hand be under the racquet. The V between his forefinger and his thumb appears to clearly be on bevel whatever it is. Clearly a Western forehand.

But the question remains…is it a strong, weak or moderate…Western forehand.

Btw Kyle…the racquet head is below his hand. See that? Guess what my next question is?

[stotty]

Also, his grip does not appear to be as extrme as I thought it would be.

Kyle LaCroix USPTA
Boca Raton

Ditto...I thought it would tad be further round also.

[johnyandell]

Kyle,

Go frame by frame and look closer at the contact point on the string bed.

[klacr]

Kyle,

Go frame by frame and look closer at the contact point on the string bed.

I went back to look. Ball flattens out a bit on the string bed as well.

Kyle LaCroix USPTA
Boca Raton

[stroke]

I would think looking at this footage that Gulbis has the heel of his hand on bevel 5, which would put him in more of a western grip than even somone like Jack Sock. Gulbis' palm, if he were to open his hand up in his forehand grip at his contact point, I would think would be completely facing the sky.

[ClassicStrokes]

Stroke,

Do you think that is a good grip? If so for who would it be best?

[stroke]

No, I am not a fan of that grip. I am a fan of forehand grips that put your hand in a strong position at your contact point. Look at Federer's and Nadal's hand/palm position at contact. That is the range I would go with, whatever you want to call the grip.

[jimlosaltos]

Fed impact stills

I went back to look. Ball flattens out a bit on the string bed as well.

Kyle LaCroix USPTA
Boca Raton

You might find these 2 stills of Fed I took at BNP Indian Wells interesting.

1) What strikes me here is how asymmetrical the back of the ball is against the closing racket face. This is at 1/3200 sec

Also, if one wants to get real geeky <g>, what I noticed in a prior one of John's extreme slowmo video's was that the ball coming off the racket is wobbling and undulating like a blob of wax in a lava lamp for the first 20 feet or so. A transverse wave from the impact surges forward, extrudes out the front of the ball, then bounces back and stretches the back of the ball again -- all while it's revolving. That means the physics are less like the Magnus effect on a curve ball and more like those of a flopping Doodoo bird <g>> Tough math to model.

FedFhdBallDeformation by james.fawcette, on Flickr

2) On this second one, you again see how severely the ball is flattened (59 lb mains, I believe) and how perhaps 4 of the cross strings are pushed down.

FedFhdBallDeformation2 by james.fawcette, on Flickr

end.

[tennis_chiro]

You might find these 2 stills of Fed I took at BNP Indian Wells interesting.

1) What strikes me here is how asymmetrical the back of the ball is against the closing racket face. This is at 1/3200 sec

Also, if one wants to get real geeky <g>, what I noticed in a prior one of John's extreme slowmo video's was that the ball coming off the racket is wobbling and undulating like a blob of wax in a lava lamp for the first 20 feet or so. A transverse wave from the impact surges forward, extrudes out the front of the ball, then bounces back and stretches the back of the ball again -- all while it's revolving. That means the physics are less like the Magnus effect on a curve ball and more like those of a flopping Doodoo bird <g>> Tough math to model.

FedFhdBallDeformation by james.fawcette, on Flickr

2) On this second one, you again see how severely the ball is flattened (59 lb mains, I believe) and how perhaps 4 of the cross strings are pushed down.

FedFhdBallDeformation2 by james.fawcette, on Flickr

end.

Fabulous pictures, Jim. How do you shoot those? What do you use?

don

[jimlosaltos]

thx

Fabulous pictures, Jim. How do you shoot those? What do you use?

don

Thanks, Don! Appreciate it.

Rented Nikon D810 and used with a 300mm 2.8 lens, which is a beast to carry but can be used in crowded stands where the 400mm lenses might not fit. Also carried a 1.7 and a 1.4x teleconverter, but don't think I used those on these 2 images.

The D810 isn't really designed for sports (not nearly as many images or as fast to focus on Nikon D4 or Canon equivalent) but the sheer pixels and sharpness help if you have to crop, as I do when sitting in the stands. And the 810 has a good dynamic range, since the light in Indian Wells is a problem (blown out highlights and dark shadows)

Let's look this up if you like the nitty gritty: ISO 100 f2.8 1/3200 -0.33ev

[klacr]

Jim,

Love the pics. Great stuff. Appreciate you sharing these for the knowledge and benefit of the rest of us tennis geeks and fans.

Kyle LaCroix USPTA
Boca Raton

[tennis_chiro]

Thanks, Don! Appreciate it.

Rented Nikon D810 and used with a 300mm 2.8 lens, which is a beast to carry but can be used in crowded stands where the 400mm lenses might not fit. Also carried a 1.7 and a 1.4x teleconverter, but don't think I used those on these 2 images.

The D810 isn't really designed for sports (not nearly as many images or as fast to focus on Nikon D4 or Canon equivalent) but the sheer pixels and sharpness help if you have to crop, as I do when sitting in the stands. And the 810 has a good dynamic range, since the light in Indian Wells is a problem (blown out highlights and dark shadows)

Let's look this up if you like the nitty gritty: ISO 100 f2.8 1/3200 -0.33ev

Jim,

I'm not much of a photographer. I let the videocamera do most of the work for me, but I am fascinated by the difficulty in catching the shot at just the right moment as you have. The fact that the picture has such high clarity tells me you can't be shooting 100's of frames per second with a mechanical shutter and we all know that ball is only on the strings for 4 thousanths of a second at most. Your timing in catching that shot has to be better than the player's timing in actually hitting it.

I'll have to look up some of your references when I get the chance, but those are just great pics!

don