Ball trajectory on a serve around impact...

[stotty]

Take a look at John Isner's second serve. Around the moment the ball is leaving the racket, is the ball travelling downwards, slightly upwards, or horizontal for a brief spell? You can use the wall where stadium seating starts as a reference point. Tell me what you think...

http://www.tennisplayer.net/members/high_speed_archive/phantom/John_Isner_HD_HS/index.html?dir=Serve/JI_Toss&stroke=JI_2ndS%20Ad%20Toss%20Side1%20500fps.mp4

I always assumed the ball travelled slightly upwards as it leaves the racket on a second serve. Am I wrong? Any thoughts, anyone?

[klacr]

The video is great, but still not 100% clear as we would need an even closer and slower look. With that said, perhaps the ball does all three things, albeit the upwards part for a brief and minimal rotation. With Isner, he's got the height so it may not be as pronounced as someone that may really need to get it up and over (Ferrer, Kohlschreiber, Rochus, Michael Russell).

To me, this video looks as though it goes horizontal, then downwards.
Many coaches may tell students to swing up on the ball, but that upwards motion may only impact the flight of the ball for the first fraction of a second as it sends it outward with just enough topspin to hold off the inevitable effects of gravity wile producing some air pressure underneath the ball and not just on top of the ball.

But what the hell do I know? It's a question that has been around for years and I simply am just guessing. Is there one solid concrete answer or is there some variance amongst player, if so, how much? The laws of physics certainly applies to everyone, but perhaps some players are capable of stretching those laws just enough to give us the illusion that something very different is happening.

The more I type in this post the more confused and curious I am getting as I'm just digging a deeper hole in search of answers.

Kyle LaCroix USPTA
Boca Raton

[tasbaron]

Nice observation. I can only imagine what it would be like to be that tall.
I'll have a go...but I'm not 100% sure. Also the parallex error makes things tricky - plus there is a missing 2 ms.

He's so tall that he can hit down on the ball with pure side spin as an option and still have the ball go in. His arm looks straight at contact so the racket head is only going sideways and forwards. It's not going upwards. The racket arm is forward and the face is pointing down. So the ball is going downwards with vicious side spin.

Could be wrong.

[stotty]

Nice observation

He's so tall that he can hit down on the ball with pure side spin as an option and still have the ball go in.

Could be wrong.

Nadal is much shorter than Isner yet the ball seems to be more clearly travelling directing down than Isner's...certainly not up it seems

http://www.tennisplayer.net/members/high_speed_archive/phantom/Rafael_Nadal_HD_HS/index.html?dir=Serve/RN_Toss&stroke=RN_2ndS_Ad_Toss_Side1_500fps.mp4

Interesting how early Nadal seems to be taking his eye off the ball....

[tasbaron]

Nadal is much shorter than Isner yet the ball seems to be more clearly travelling directing down than Isner's...certainly not up it seems

http://www.tennisplayer.net/members/high_speed_archive/phantom/Rafael_Nadal_HD_HS/index.html?dir=Serve/RN_Toss&stroke=RN_2ndS_Ad_Toss_Side1_500fps.mp4

Interesting how early Nadal seems to be taking his eye off the ball....

I think the parallex error here is even worse due to the elevated camera view point. Note the horizontal line in the background falls to the left. So a horizontally moving ball will appear to fall as it moves to the left.

Plus, in the missing two milli-seconds between frames, the ball may have dropped below its apparent exit height, and we miss the slight rise.

Or maybe, he's just hitting slice. He is left handed, hitting to the adv side.
The angle of elevation may only be a fraction of a degree.

Maybe that's the secret... Don't watch the ball!?

[bottle]

Fantastic that you (Stotty) presented some shorter guy-- never heard of him-- effectively hitting down on the ball. Revise: Hitting up on a ball with slant in the racket that is about to make that ball go down.

(Just saw Barra's post. But am not ready to buy into the fanciful notion that ball is going up before it goes down in two microseconds we can't see. Am remembering that Australian sport scientist and my best doubles partner also showing to get the racket slanting forward but maybe have forgotten whether this advice was aimed only at tallbies. Judging from Stotty's video of Nadal probably not. On the other hand maybe any ball carrying topspin tries to go up and if so why not at the moment when topspin is greatest as ball comes off strings except for that other moment when the court adds to the topspin? Because ball has also been smacked besides scraped to answer my own question and may have to slow down for the spin to take effect. But only a thirst for the truth would make one concerned with some rise after contact that none of us can see, and hey, is this physics or tennis and what does truth have to do with tennis? Well, a lot. The best truth here though may be the simple advice to slant the racket forward so that a perpendicular from it points slightly down. Note: the slant may get the racket to pass over the ball's upper right quadrant. Try in office when boss, who doesn't know you have a racket in office, isn't there. More upward component occurs when racket passes over that quadrant.)

[lobndropshot]

It is geometrically possible to hit down on the ball from 8.6 feet above the baseline. This doesn't take gravity or air resistance into account when those two elements are added to the equation that actually lowers the minimum height at which you can hit the ball at a downward angle.


TAN^-1((3/21)) = 8.13 Degrees

so

TAN(8.13)*60=X
X= 8.57 feet

[stotty]

A riddle

I find it a little intriguing that when a player hits up on the ball to hit a kick serve, the ball does not go up initially as it leaves the racket: otherwise how does he get such high net clearance typical of a good second serve? It doesn't make sense.

None it matters a whole hill of beans really, as players have always done these things without needing to know the science. Nevertheless, I'd like answers...

[johnyandell]

Yes clear answers are good.

[tennis_chiro]

Isner's racket face ascending at contact!

Look carefully at Isner's racket against the wall in the background. At first contact with the ball, it is only slightly above the wall in this view. A couple of frames later as the ball leaves the strings, the tip of the racket actually is at least 2 or 3 inches higher as John reaches full extension. His hand may not be any higher; in fact, it may actually be a little lower, but because of ulnar deviation, the racket head and, therefore, the strings are rising as they brush the ball imparting topspin as well as sidespin.

don

[stotty]

Look carefully at Isner's racket against the wall in the background. At first contact with the ball, it is only slightly above the wall in this view. A couple of frames later as the ball leaves the strings, the tip of the racket actually is at least 2 or 3 inches higher as John reaches full extension. His hand may not be any higher; in fact, it may actually be a little lower, but because of ulnar deviation, the racket head and, therefore, the strings are rising as they brush the ball imparting topspin as well as sidespin.

don

That's a terrific observation. I was focusing so much on the flight of the ball leaving the racket that I had completely failed to factor in other data like whether the racket head was rising. How can I have watched a clip so many times and fail to notice that!

[bottle]

I neither claim to have done this or that I necessarily ever will be able to do this-- and I'm looking at Stotty's riddle too.

Before delivery of my little guess, however, I'd like to be very straightforward and simple.

My best doubles partner ever, a former hockey goalie from New England who was 6'6" would tune his serve by holding up the ball and contacting it in mime with forward slant. HIS SERVE GOT BETTER EVERY TIME HE THOUGHT TO DO THIS.

And mine seemed to go twice as fast yesterday after I remembered to try that.

The little guess now as to an answer to the riddle: extreme spin has been administered but hasn't had time yet to take effect.

But spin effect like lake effect around the Great Lakes happens before the net in microseconds we can't see since the camera wasn't even focused there hence the high clearance.

If this guess is poppycock I think that ball got to its reasonable apogee via only slightly downward line drive, and I defer to lob&dropshot's formula:

TAN^-1((3/21)) = 8.13 Degrees

so

TAN(8.13)*60=X
X= 8.57 feet

[lobndropshot]

If a ball is struck at an angle parallel to the court with zero spin and no air resistance from 9 feet above the ground it will land on the ground in .748 seconds. Therefore, the maximum velocity a ball can travel in 60 feet and .748 seconds is 54.69 Miles per hour.

I guess the if goal is the to decrease the amount of time it takes the ball to travel 60 feet you must hit the ball at an angle less than parallel to the court? or increase the magnus effect on the ball. Can you increase the magnus force on the ball to the point where in .27 sec it travels 60 feet and hit the ball at an upward angle? I am not sure. I don't know how to calculate that at this time. But my gut is telling me that the ball must hit at a slight downward angle.

I hope this post makes sense....

[stotty]

If a ball is struck at an angle parallel to the court with zero spin and no air resistance from 9 feet above the ground it will land on the ground in .748 seconds. Therefore, the maximum velocity a ball can travel in 60 feet and .748 seconds is 54.69 Miles per hour.

I guess the if goal is the to decrease the amount of time it takes the ball to travel 60 feet you must hit the ball at an angle less than parallel to the court? or increase the magnus effect on the ball. Can you increase the magnus force on the ball to the point where in .27 sec it travels 60 feet and hit the ball at an upward angle? I am not sure. I don't know how to calculate that at this time. But my gut is telling me that the ball must hit at a slight downward angle.

I hope this post makes sense....

Its all getting a bit Harold Brody if you ask me. Clearly a ball struck flat can only be struck so hard from a given height and go in. I understand the math on that one.

I think most of us seem to see the ball as descending the moment it leaves the racket, but I think tennis_chiro is onto something in his observation that racket is still rising upwards as the ball leaves the strings. I just find it hard to understand the net clearance issue. You would think there might be a slight upward movement of the ball as it leaves the strings.

[lobndropshot]

Its all getting a bit Harold Brody if you ask me. Clearly a ball struck flat can only be struck so hard from a given height and go in. I understand the math on that one.

I think most of us seem to see the ball as descending the moment it leaves the racket, but I think tennis_chiro is onto something in his observation that racket is still rising upwards as the ball leaves the strings. I just find it hard to understand the net clearance issue. You would think there might be a slight upward movement of the ball as it leaves the strings.

Why would you think that there would be a slight upward movement after contact?
Just curious... Is it because the movement of the racket at contact?