Kick Vs. Topspin Serve; one and the same?!

[Relinquis]

Thanks for all of the detailed responses guys.

How does one go about imparting spiral spin on the ball?

Does this kick serve have a bit of spiral spin?
http://www.youtube.com/watch?v=mM1P2ej4YtY

[TheCheese]

Kick serves change direction on the bounce. Breaks right for a righty, left for a lefty. Aka American Twist serve.

You basically hit it the same as a topspin serve, but get around the side of the ball a little more. If you're right handed, think of a standard topspin serve as hitting from 6 to 12 o'clock if you can imagine a clock face on the back of the ball. A kick serve should be 7 to 1 or further over. You should be able to hit this with the same toss as your topspin serve.


Also, I disagree with this graphic:

Really, you should be able to hit every serve from the topspin/slice serve position. For kick or topspin, just move the ball toss closer to the baseline (less in front). This makes it impossible for your opponent to read your serve based on your toss.

[SystemicAnomaly]

NadalDramaQueen:

Curious that you deleted your post as I was about to reply to it. FYI, Rod Cross is a retired physics professor from the University of Sydney (but still appears to be member of the university staff). He has a PhD in plasma physics and is also considered an expert in sports mechanics and forensic physics. TWU (Tennis Warehouse University) was developed by Rod Cross and Crawford Lindsey.

These 2 men co-authored Technical Tennis which talks about spiralspin in some depth. They also collaborated with physicist, Howard Brody to write The Physics and Technology of Tennis. In the following TWU article, Physics of the Tennis Kick Serve, Rod Cross talks a bit about gyrospin (aka spiralspin or corkscrew spin).

http://twu.tennis-warehouse.com/lear.../kickserve.php

[travlerajm]

Originally Posted by SystemicAnomaly

^ You are incorrect about corkscrew spin in tennis. Physicist, Rod Cross, had thought very much about the physics of tennis and disagrees with you. One does not hit the side of the ball to impart corkscrew spin. However, the contact is offset to impart this type of spin.

This type of spin can also be imparted to underhand shots with very dramatic effects.

Corkscrew spin on a twist serve is negligible. Cross mentions spiralspin as the type of spin put on a football. He suggests that it is possible for tennis. However, he didn't find much spiral spin on twist serves.

As for underhand shots (or to a smaller extent for a twist serve with initial upward trajectory), the spiralspin is initially zero, but increases as gravity changes the path of the ball. The spin immediately after contact with the strings is not sprialspin - a tennis racquet is not designed to impart spiralspin.

[SystemicAnomaly]

Originally Posted by travlerajm

Corkscrew spin on a twist serve is negligible. Cross mentions spiralspin as the type of spin put on a football. He suggests that it is possible for tennis. However, he didn't find much spiral spin on twist serves.

As for underhand shots (or to a smaller extent for a twist serve with initial upward trajectory), the spiralspin is initially zero, but increases as gravity changes the path of the ball. The spin immediately after contact with the strings is not sprialspin - a tennis racquet is not designed to impart spiralspin.

This is not what Rod Cross says in his book, Technical Tennis. I suggest you give it a read before passing judgement. There is no other way to explain the behavior of the ball flight and bounce. Rod Cross very explicitly states that regular sidespin has ZERO direct effect on the bounce direction. Whereas spiral spin does not affect flight trajectory but does influence bounce direction.

Gravity has nothing at all to do with imparting spiral spin to the ball. Maximum spiral spin is achieved at contact with the racquet, not sometime later.

In tennis, it is true that we usually cannot impart as much spiralspin to the ball as we can topspin (or sidespin) for a serve. However, it is not at all negligible as evidenced by the bounce direction. There is an underhand shot in tennis that exhibits quite a bit more spiral spin than the twist serve. Players will sometimes take a vicious swipe left-to-right (or right-to-left) to the back/underside of the ball. It is as if you were drawing a smile on the lower part of the ball (but not on the very bottom of the ball). This action will usually produce a bit of underspin with some regular sidespin and a massive amount of spiral spin if executed correctly. With this novelty shot, I've gotten the ball to bounce nearly parallel to the net due to the presence of spiralspin.

[SystemicAnomaly]

Originally Posted by Relinquis

... How does one go about imparting spiral spin on the ball?

Does this kick serve have a bit of spiral spin?
http://www.youtube.com/watch?v=mM1P2ej4YtY

It most definitely has a decent dose of spiralspin with a generous amount of topspin. His serve only had a moderate amount of sidespin but it does intially curve in a bit toward the returner. Once it bounces, however, the spiralspin action causes the ball to kick away from the returner very dramatically.

Usually right-handers will hit this type of serve on the ad side. However, Roger does it very effectively here on the deuce side. It appears that he contact the ball a little bit to the left of his head. He is brushing upward on the right side of the ball -- instead of thinking a straight diagonal 7 to 1 brush, I would think of it more like arc brush from 7 to 12 or 7 to 11.

Originally Posted by TheCheese

Kick serves change direction on the bounce. Breaks right for a righty, left for a lefty. Aka American Twist serve.

You basically hit it the same as a topspin serve, but get around the side of the ball a little more. If you're right handed, think of a standard topspin serve as hitting from 6 to 12 o'clock if you can imagine a clock face on the back of the ball. A kick serve should be 7 to 1 or further over. You should be able to hit this with the same toss as your topspin serve.

Also, I disagree with this graphic:

Really, you should be able to hit every serve from the topspin/slice serve position. For kick or topspin, just move the ball toss closer to the baseline (less in front). This makes it impossible for your opponent to read your serve based on your toss.

The graphic was originally from the Operation Doubles.

Coaches have been claiming for years/decades that the toss should be the same for all serves. This is simply not practical at all for a variety of serves for most servers. Even elite servers like Pete Sampras did not toss the ball to the same location for all serves. He claimed that he had 2 different tosses. Some servers may employ 3 different tosses. However, the difference between those different tosses is quite a bit less for many elite servers than for non-elite tennis players.

Federer appears to have a lower toss than Sampras but employs a wider toss arc. He seems to intercept the ball trajectory at different places in that arc for different serve types (& placements). It is likely that he employs more than one type of toss as well. However, like Sampras, the changes are more subtle than it would be for most of us.

It is no secret that most servers will hit the first serve flatter than the 2nd serve. There is really is no reason to hide that fact. It is much more important to disguise the intended placement of your server rather than trying to disguise the type of serve.

[travlerajm]

Originally Posted by SystemicAnomaly

This is not what Rod Cross says in his book, Technical Tennis. I suggest you give it a read before passing judgement. There is no other way to explain the behavior of the ball flight and bounce. Rod Cross very explicitly states that regular sidespin has ZERO direct effect on the bounce direction. Whereas spiral spin does not affect flight trajectory but does influence bounce direction.

Gravity has nothing at all to do with imparting spiral spin to the ball. Maximum spiral spin is achieved at contact with the racquet, not sometime later.

In tennis, it is true that we usually cannot impart as much spiralspin to the ball as we can topspin (or sidespin) for a serve. However, it is not at all negligible as evidenced by the bounce direction. There is an underhand shot in tennis that exhibits quite a bit more spiral spin than the twist serve. Players will sometimes take a vicious swipe left-to-right (or right-to-left) to the back/underside of the ball. It is as if you were drawing a smile on the lower part of the ball (but not on the very bottom of the ball). This action will usually produce a bit of underspin with some regular sidespin and a massive amount of spiral spin if executed correctly. With this novelty shot, I've gotten the ball to bounce nearly parallel to the net due to the presence of spiralspin.

I respectfully disagree. I have not read Technical Tennis in many years, but have read all of his short publications I must say that I have found several occasions where I disagree with Cross. And in at least one occasion, I have found his interpretation to be easily disproved. It is possible that this is another.

It is easy to show that a very decent twist serve can be hit with a dual-wheel ball machine that delivers zero initial spiralspin.

And again, the spiralspin in an underhand sidespin serve applied to the underside of the ball is maximized at the bounce, not at the strings. The same is true of a twist serve.

[TheCheese]

Originally Posted by SystemicAnomaly

The graphic was originally from the Operation Doubles.

Coaches have been claiming for years/decades that the toss should be the same for all serves. This is simply not practical at all for a variety of serves for most servers. Even elite servers like Pete Sampras did not toss the ball to the same location for all serves. He claimed that he had 2 different tosses. Some servers may employ 3 different tosses. However, the difference between those different tosses is quite a bit less for many elite servers than for non-elite tennis players.

I'm advocating keeping the position of the toss the same while varying how far you throw it into the court. So, yes different toss positions, but because you're only varying how far you throw it into the court it's essentially impossible to read from where the returner is standing.

[pvaudio]

Originally Posted by SystemicAnomaly

Close, but not quite.

A serve whose spin is primarily side-spin (vertical-axis), will not normally kick. As psv255 and I have indicated, a kick serve normally requires a significant topspin component. Vertical-axis sidespin will only affect the left/right deviation of the ball traveling thru the air (Magnus Effect). This type of spin has no direct effect on the bounce (direction or height). Physicist, Rod Cross, had indicated this in some of his writings on tennis physics.

However, it you lob the serve with an open racket face with sidespin, it will bounce quite high even tho' it may not have very much topspin. This high bounce might be considered a kick by many.

A topspin serve or a topspin kick serve will usually also have a small amount of a sidespin component (just as most slice serves will have some degree of a topspin component). If your serve has sufficient components of both topspin and sidespin, we refer to it as a topspin-slice serve.

The "reverse bounce" seen in the twist version of the kick serve is due to spiral spin and not due to our garden-variety (vertical axis) sidespin. Think of the spin on the spiral pass of an American football or the natural spin on a badminton shuttle. This is spiral spin -- also known as spiralspin, gyrospin, corkscrew spin (or cork spin in table tennis). Its axis of rotation is more-or-less horizontal and in the direction of the flight path of the ball (or shuttle).

There is no Magnus effect associated with spiralspin so it has no effect on the trajectory of the ball as it flies thru the air. This is why spiral spin is often applied to bullets (with rifling of the barrel) and sometimes to arrows. However, when a ball with spiralspin hits the ground, it will bounce to the left or the right.

If the ball has mild spiraspin, then the left/right bounce deviation will be only slight. We might see this with a topspin-slice serve. If the spiralspin is negligible, then after the bounce, the ball will continue in the same direction is was traveling immediately prior to the bounce. If this serve has a moderate amount of spiralspin then we will see the ball direction straighten out with the bounce.

We might refer to a kick serve that does this as a twist serve -- cuz the ball is moving in a direction after the bounce that is somewhat different than the pre-bounce direction. It the amount of spiralspin is relatively generous on a topspin-slice kick serve, then the effect is very dramatic. The ball path curves in one direction (left or right) prior to the bounce due to (vertical-axis) sidespin. However, the ball bounces in the opposite direction due to the spiralspin component. This action is what we normally think of when we refer to a twist serve.

This corkscrew spin business is not easy to understand because you cannot picture it easily. Here is the best way to do so, IMO. Either imagine or put a tennis ball in front of you. There are 3 directions: x (left and right), y (forward and backwards) and z (upwards and down, aka into the air or through the table). Top spin is a pure positive y direction forwards spin, as in the ball will roll away from you. Backspin is the negative y direction, as in towards you. Side spin is a pure x direction spin, so either rolling to the left or the right. The corkscrew spins ABOUT the z-axis. It does not move in space, it simply sits where you puts it and spins. To picture that, imagine spinning the ball like a top. There's your z-axis or corkscrew spin.

Indeed, your analysis is correct. It's generating that extra component that causes the twist portion. It's how you generate it that causes all of the difficulty with this serve.

[SystemicAnomaly]

Originally Posted by pvaudio

This corkscrew spin business is not easy to understand because you cannot picture it easily. Here is the best way to do so, IMO. Either imagine or put a tennis ball in front of you. There are 3 directions: x (left and right), y (forward and backwards) and z (upwards and down, aka into the air or through the table). Top spin is a pure positive y direction forwards spin, as in the ball will roll away from you. Backspin is the negative y direction, as in towards you. Side spin is a pure x direction spin, so either rolling to the left or the right. The corkscrew spins ABOUT the z-axis. It does not move in space, it simply sits where you puts it and spins. To picture that, imagine spinning the ball like a top. There's your z-axis or corkscrew spin.

Indeed, your analysis is correct. It's generating that extra component that causes the twist portion. It's how you generate it that causes all of the difficulty with this serve.

Very good explanation. Below is a visual aid that shows the 3 (reference) axes of rotation. This is a repost of mine from 2011:

Imagine, if you will, that this airplane is flying away from us -- we are viewing it from the back. We have 2 horizontal axes of reference. Let's call the Purple (Pitch) axis our X-axis. This axis would be akin to the axis of rotation for topspin and underspin. This axis is perpendicular to the direction of flight.

The Red (Roll) axis is our other horizontal axis. I will refer to this as the Z-axis. This would be the axis of rotation for spiral spin -- the axis is in the the Z direction, the same as the flight of the airplane or ball.

The Yellow (Yaw) axis is our vertical axis and is perpendicular to the direction of travel. This is the axis of rotation for the spin that we refer to as sidespin.

[SystemicAnomaly]

Here are a couple of links of my posts from 2008 & 2009 that might shed more lights on X, Y and Z axis spins:

http://tt.tennis-warehouse.com/showt...19#post3703619

http://tt.tennis-warehouse.com/showt...41#post2805941

The following link talks a bit more about Z-axis spin (aka bullet spin):

http://tt.tennis-warehouse.com/showt...45#post6499645


In the old Operation Doubles web site, Kathy Krajco talks about the altered axis of rotation for a twist serve. She does not give a name to the Z-axis component of spin but she does talk about how the resultant spin axis is different for a twist serve than it is for a regular topspin-slice serve.

For most shots that we discuss in tennis (with topspin, underspin & sidespin), the actual axis of rotation of the spinning will be perpendicular to the flight of the ball. However, due to the presence of a Z-axis spin, the actual rotation of the ball on a twist serve is no longer perpendicular to the flight of the ball -- it is offset somewhat from the perpendicular.

Here is an archive of the late Kathy Krajco's old OD web site page. Unfortunately, some of her excellent gifs showing the spins may no longer work:

http://web.archive.org/web/200812171...oringserve.htm

[NadalDramaQueen]

Originally Posted by SystemicAnomaly

NadalDramaQueen:

Curious that you deleted your post as I was about to reply to it. FYI, Rod Cross is a retired physics professor from the University of Sydney (but still appears to be member of the university staff). He has a PhD in plasma physics and is also considered an expert in sports mechanics and forensic physics. TWU (Tennis Warehouse University) was developed by Rod Cross and Crawford Lindsey.

These 2 men co-authored Technical Tennis which talks about spiralspin in some depth. They also collaborated with physicist, Howard Brody to write The Physics and Technology of Tennis. In the following TWU article, Physics of the Tennis Kick Serve, Rod Cross talks a bit about gyrospin (aka spiralspin or corkscrew spin).

http://twu.tennis-warehouse.com/lear.../kickserve.php

Thanks for the information, and sorry that I deleted my post. I can get too carried away when talking of physics and I fear that I will sacrifice my own privacy.

I will continue following the thread.

[travlerajm]

Most everyone posting in this thread is missing the main point:

Sprialspin exists in tennis, but it is not applied directly by a tennis racquet.

For easier visualization, consider the extreme case of an underspin spiralspin serve.

At the moment of contact with the stringbed, the racquetface is aimed about 45-degrees upward. Thus the strings contact the surface of the ball about midway between the bottom of the ball and the back of the ball, and maybe a little bit to the side of the ball.

And at the moment of contact with the stringbed, the swingpath of the racquet is very fast in a right-to-left direction.

I think we all agree that the effect of this type of serve is a sharp bounce to the right.

At the moment of contact, 0% of the spin is sprialspin, because the spin axis is perpendicular to the flight path. But as gravity acts on the ball through its arc, the flight direction changes. At the moment of the bounce, the ball is moving downward in roughly a 45-degree angle. The flight path has veered by 90 degrees over the arc of travel, but the spin axis has stayed the same. Nearly 100% of the spin is now spiralspin at the moment of the bounce. Thus, gravity has converted all of the spin to sprialspin.

This also happens in a twist serve, but the conversion to spiralspin is not as extreme.

When you serve in pingpong, you can "corkscrew" the paddle into the ball by rotating the handle around the impact point. So a pingpong paddle can apply a torque around the z axis. You can't do that with a tennis racquet. A tennis racquet only applies normal force and tangential force to the ball. These two vectors together are not enough to cause spiralspin - you need a third vector. That third vector is supplied by gravity.

A twist serve is really not that complicated.

[SystemicAnomaly]

^ I do not believe that I am missing the point at all. However, I am not following you on the points that you are attempting to make. I do not agree with your assertion that we cannot apply spiral spin with the racquet. For the underspin shot you speak of, the axis of rotation is not perpendicular to the flight of the ball. In fact, it is more in line with the path of the ball. I am not following your thinking on this.

I have not just blindly accepted everything that Rod Cross has said about spins and their effect on trajectories and bounces. Because much of this stuff is not intuitive, I've had to prove it for myself with fairly simple, informal experiments. Everything that I've tried bears out what Rod Cross, Howard Brody, Kathy Krajco and others have said about the various spins that can be imparted to a tennis ball.

For instance, I was skeptical about the claim that (vertical-axis) sidespin does not directly affect the bounce of a ball. I performed a series of tests with tennis balls (as well as with a basketball and a volleyball). The tests included imparting a vertical axis spin while dropping a ball, while throwing a ball and while hitting a ball (with a racquet). I compared these various tests to ones where little or no spin was imparted to the ball. No effect to the bounce was detected with vertical-axis spin.

I've conducted similar tests with topspin, underspin and spiralspin. Topspin and underspin was seen to have an effect on both the flight trajectory and the bounce. Different effects were noted for different angles of incidence on the bounce.

With spiralspin, no effects were detected during flight but very significant effects where seen on the bounce. Note that the post-bounce spin was primarily topspin regardless of the type of prebounce spins present. In the case of a ball bouncing off to the side (due to spiralspin) or a ball bouncing backward (due to an overpowering underspin), the ball took on a topspin in the new direction. However, we might consider the ball bouncing backward as still having underspin with respect to our original frame of reference -- but it is really just topspin in the new direction.

Why do you believe that table tennis players can impart spiral spin (corkscrew spin) but tennis players cannot? I can impart corkscrew spin to a ping pong ball with a simple brushing motion -- just as I would do with a tennis ball and racquet. The corkscrew technique that you describe for ping pong might very well yield a more dramatic cork spin then I can with my simple brush -- but I can still apply the spin with a simpler motion. The degree of spin potential is different for for ping pong than for tennis but the basic ideas of spin are the same.
.

[SystemicAnomaly]

If I gently hit the ball with a moderate amount of brushing to impart a spiral spin, I can clearly see that the ball has a strong component of spiral spin from the onset. The axis of rotation is clearly not perpendicular to the flight of the ball in this case. For those of you still following along -- the axis of rotation of a spinning ball is perpendicular to the direction of its spin. For example, the spin for a pure topspin ball is in the direction of the flight of the ball. However, its axis of rotation is perpendicular to the flight. The same is true for underspin and both flavors of vertical-axis spin (sidespin). OTOH, just the opposite is true for both flavors of spiralspin -- spin is perpendicular to the flight but the axis of rotation is in the same direction as the flight of the ball.

While spiralspin spin was very evident at the onset (coming off the strings) in my experiment, its effect is not manifested until the bounce. Spiral spin is not caused by the bounce -- it is already present and affects the bounce. Gravity is not magically producing spiralspin either -- the spin happens as a direct and immediate effect of the brushing motion.

[Dimcorner]

I'm confused. You can hit a ball forward and make it spin like a bullet?

[luvforty]

nah, has to be a combo of top spin and bullet spin.

[SystemicAnomaly]

Originally Posted by luvforty

nah, has to be a combo of top spin and bullet spin.

Or it can be underspin with bullet spin. If you try to hit bullet (spiral) spin without also hitting topspin or underspin, the ball will not go forward. When imparting bullet spin to the ball with a tennis racquet there will also be some regular side spin -- it is unavoidable.