# Mathematic Serving

Discussion in 'Tennis Tips/Instruction' started by db10s, Dec 1, 2012.

1. ### db10sHall of Fame

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I know it would be hard to process this while serving, but it is still a good explanation for why, and how, things happen. I know some of you may find this interesting: http://plus.maths.org/content/spinning-perfect-serve

2. ### sureshsBionic Poster

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Once again confirms that the kick of the ball is not due to the topspin interaction with the ground, but the already higher point from which a topspin ball drops to the ground: "The steeper angle makes the bounce higher"

3. ### pvaudioLegend

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This does not confirm anything as it's saying just that. You're wanting to describe an incomplete picture with only half of the situation. In the other thread, I gave the example of dropping a ball from 8 feet straight up and down, say a lob into the service box. You could tee off on that without any difficulty. The reason the topspin serve is so nasty is not because of the steeper angle. It's because it has BOTH the steeper incident angle, and greater incident velocity due to the Magnus force. In other words, it is carrying extra momentum in its spin which, due to the ground, gets translated into a higher and more difficult bounce. The topspin serve takes a portion of its horizontal velocity (towards the opponent) and turns it into vertical velocity as the magnus effect forces the ball to the ground more quickly than gravity alone. No matter what the physics, if the ball bounces differently even though it looks the same, then something applied a force to something. In this case, the ball applied more force to the ground. The angle of incidence itself is simply a component of all of these interactions.

4. ### LeeDBionic Poster

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All part of the whole equation. Angle in incidence, spin of ball, speed of ball, depth of ball, ALL make a difference, and cannot be separated into it's individual parts.

5. ### sureshsBionic Poster

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Sounds good.

One question I have is that while part of the energy goes into the rotation, which causes a pressure differential and a net downward force in addition to gravity (and so a higher incident speed at bounce), would the same higher incident speed be achieved by a flatter shot which did not put energy into rotation in the first place?

In other words, if Karlovic hit a flat serve and achieved a certain incident speed at bounce, and then hit a topspin serve with lower speed towards the target, could the two incident speeds at bounce be the same? The input "energy" is assumed to be the same in both cases i.e. Ivo spends the same number of calories for each.

To me it seems the flat serve will have a faster incident speed, even though the topspin serve might descend from a higher height and have the Magnus force pushing down too. What do you think?

Last edited: Dec 1, 2012
6. ### LeeDBionic Poster

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Now we're getting really finite...
A flat serve is usually hit with less RHS than a first spin serve.
A flat serve usually bounces lower than any topspin serve.
A flat serve goes faster, which is why.
Sorry, gotta go, g/f wants me to check out a boom for her new 7.5 Gaastra Vapor Race sail...

7. ### dominikk1985Legend

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not just the higher drop but also the higher downward energy as the ball not just dops by gravity but is actively "sucked" down by the magnus effect.

but I agree the spin itself doesn't increase bounce angle (the opposite is actually true).

8. ### 10sLiferNew User

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Yes. Trajectory determines the height of the bounce much more than spin...

9. ### LeeDBionic Poster

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The surrounding enviorment also helps determine bounce.
Temps, court surface, ball used, strings, rackets, which player, besides just trajectory, spin, altitude, which planet....

10. ### defruleProfessional

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I think spin might have an effect but I could be wrong.

Imagine the court deforming downwards very slightly when the ball lands. This crater-like shape is no longer horizontal and the ball's spin would grab onto the side of the crater which is inclined upwards and accelerate it upwards.

I could be wrong but it seems to me that even average net clearance balls can be made to explode off the court.

11. ### sureshsBionic Poster

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I think the explosion is a myth. It appears to be an explosion because the ball lands earlier than we expect and bounces higher than we expect.

12. ### pvaudioLegend

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Both correct, and both because there is a large amount of spin on the ball. This does not happen with a flat ball, so logic lets us deduce that the spin causes this effect. The mechanism that the spin makes happen is, IMO, irrelevant (increased incident angle, greater static friction on the court surface, etc.) since it doens't occur if the ball doesn't have RPMs on it.