Discussion in 'Tennis Tips/Instruction' started by toly, Sep 14, 2012.

1. tolyHall of Fame

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Anatoly Antipin

Twist Serve

To create twist serve we have to brush a ball approximately from 8:00 to 2:00 o’clock, but above the ball’s equator. This kind of brushing motion creates topspin, sidespin, and spiralspin (gyrospin).

The spiral/gyro spin would be in clockwise direction causing the ball bounce deviation toward the right. The gyrospin motion rotates the ball about an axis pointing towards the target. That sort of spin is used to throw a gridiron football, but it has no effect on curvature of the ball through the air.

We can hit the ball above its equator if and only if the racquet face is tilted forward - slightly closed.

There is example of the racket motion around impact in case of twist serve.

Figure 1. The racquet’s movement around contact

The frame #2 is point of contact. The arm itself moves relatively slowly forward, to the right, and downward and practically doesn’t affect racquet brushing motions.

On the other hand, the wrist ulnar deviation rotates, very fast, the racquet upward and to the right almost perpendicular to the ball outgoing direction.

It seems, the wrist ulnar deviation produces the main contribution to the topspin, sidespin, and gyrospin. All others motions of the body (arm pronation, wrist flexion, and so on) create mostly translational motion of the ball.

Figure 2. The tilted forward racquet

The theta (ϴ) angle defines magnitude of the gyro and side spins.

Figure 3. Vector of the spin component along with its components

Assume that the racquet face tilted forward with theta angle (ϴ). Then gyrospin, sidespin, and topspin racquet's velocity components would be:

VGyrospin = VSpinHor*sin(ϴ) (1)

VSidespin = VSpinHor*cos(ϴ) (2)

VTopspin = VSpinVer (3)

The more we tilt the racquet face forward (increase ϴ), the more efficient would be gyrospin and less effective sidespin.

If ϴ =45° then VGyrospin = VSidespin , but I doubt that one can hit successful twist serve with so large theta angle.

Btw, topspin component isn’t affected by ϴ.

The theta angle also determines coordinates of the point of contact, see picture below.

Figure 4. The tilted forward racquet and ball’s equator

IMO ϴ should be less than 30° and thus point of contact would be next to ball’s equator, otherwise the ball goes into net.

Last edited: Sep 19, 2012
2. LeeDBionic Poster

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Too much conjecture. Just go out to the courts, toss above your head, strike the ball with the racket moving upwards, clear the net by 3', and the resultant twist serve bounces head high, opposite direction of the flight.

3. Raul_SJHall of Fame

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I will study this...

I am not clear on the "8 o'clock to 2 o'clock" brushing motion.
I am using that for a Topspin serve -- where the bounce is pretty much straight ahead.

4. NTRPoliceProfessional

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You also need to consider where you're serving from and where you're serving to. All the times ive hit this serve were on the deuce side serving down the middle.

I dont "try" to do this serve, but sometimes it just happens when im trying to serve a normal kick serve. I only realize ive hit this serve after I see the action on the ball (and usually the opponents getting all jammed up lol)

5. RoforotProfessional

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I don't know about the math or physics, but I'm interested in trying out these ideas on the court. I can hit a twist serve, but I'd like to be able to mix it up and just hit a topspin serve so they don't get used to the sidespin. It sounds like tilting the racquet head forward should accomplish this.

6. LimpinhitterG.O.A.T.

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Zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz . . . who, whah! Oh, it's Toly again. Smack, smack . . . yawwwwwn . . . zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz!

7. tolyHall of Fame

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When we hit topspin serve the theta angle is usually around zero degree ϴ =0°. Then, according to formulas (1), see post #1

VGyrospin = VSpinHor*sin(ϴ) = VSpinHor*sin(0°) = 0

So, the ball doesn’t bounce to the right.

Because of different magnitude of ϴ we can swing from 8:00 to 2:00 and produce different ball’s rotation.

Last edited: Sep 19, 2012
8. spacediverHall of Fame

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well done toly - your posts are becoming clearer. Only critique is that there was one sentence in there that was "borrowed" from an article by rod cross (about the gridiron football).

9. tolyHall of Fame

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Thanks to you, I learned a lot about proper medical and tennis slangs.

Yes, I stole the Rod Cross sentence, because I know nothing about football and my English is still very poor.

10. tolyHall of Fame

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Can you evaluate the theta angle when you hit decent twist serve?

11. BowtiesarecoolRookie

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It is my understanding that the kick serve bounces away as a result of how the ball deforms when hitting the ground at such a steep angle with heavy topspin. I have seen computer simulations of this effect, but can't remember where to find them.

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13. directionalsRookie

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If the ball is struck at above the equator, then I don't understand why people say hit the ball from 8 o'clock to 2 o'clock. Shouldn't that be 10 o'clock to 2 o'clock then?

14. tolyHall of Fame

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If you brush the ball from 10 o’clock to 2 o’clock, angle theta would be around 30 degrees (ϴ = 30°) and this brush motion creates only horizontal component VSpinHor, see post #1, fig.3.

Topspin component of the racquet velocity will be zero, VTopspin = VSpinVer = 0. With tilted racquet (ϴ = 30°) and without topspin you definitely hit the ball into net.

There is simple approximate rule: For every degree of closed racquet face you have to swing the racquet the same degree upward. So, topspin component is very important for twist serve.

That’s why you have to swing from 8 o'clock to 2 o'clock. If ϴ is more 15° you maybe should brush the ball from 7 o'clock to 1 o'clock.

Last edited: Sep 21, 2012
15. sureshsBionic Poster

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I was also confused, then I realized he means 8 to 2 overall, but contacting the ball from 10 to 2. Before that the swing was in the air.

16. xFullCourtTenniSxHall of Fame

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If you knew nothing about how to hit a kick serve, and I gave you this information (this thread) to teach you, how likely do you think you will be able to learn it? The answer is very unlikely.

People need simple cues and simple directions to do what they need to do, then let the body figure out the rest itself in a way that is comfortable.

If I told you 10 to 2, then you won't be aiming for much of a vertical factor in your swing. As a result, you will have trouble getting the ball over the net and getting the kick you want (especially when hitting the ball "above the equator").

If your kick serve has no kick to it, then returning the serve is about as difficult as returning a slice serve, it's not an issue unless you disguise both serves to look the same and vary your placement very well. It's the kick that makes it a problem. The "twist" just confuses inexperienced players and makes it look pretty.

17. TennisCJCLegend

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I think some of the information in your theory comes from this TWU article http://twu.tennis-warehouse.com/learning_center/kickserve.php that supports more spin being generated if you strike the top of the ball. I have also seen other web instruction that you must get the racket head in front of the wrist to hit a good kick serve too and this supports your theory also.

I have an OK kick serve - not great - but I target the bottom inside and swing up to the top outside at almost a 45 degree angle thru the ball. I do try to keep the shoulders turn, swing more at the side fence and get the racket head through the ball - racket head slightly in front of wrist.

In reality, the racket probably does brush across the top of the ball as you indicate. Maybe contact the bottom or center but brushes across the top before the ball leaves the strings.

18. tolyHall of Fame

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To clarify the matter, there is one more example - Ryan Chung hits unreturned twits serve around 8:13

I extracted four frames from this video.

Figure 5. Ryan Chung's twist serve

Chung tosses the ball very far to the right. During contact the racquet is slightly closed and he hits the ball above its equator. This is really very complicated serve. :shock:

Last edited: Sep 29, 2012

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20. SystemicAnomalyG.O.A.T.

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Are you talking about kick serves, in general, or specifically twist kicks? The term, kick serve, is somewhat generic/ambiguous. Some use the terms, kick serve & twist serve, as synonyms. Whereas others classify the twist serve as a specific type of kick serve. In this taxonomy, a kick serve is any serve with heavy topspin that kicks upward on the bounce. If the kick serve curves one way, in pre-bounce flight, and then kicks off in the opposite direction on the bounce then it qualifies as a twist serve. If the kick does not deviate appreciably left or right on the bounce then it would be a topspin kick (or a topspin-slice kick) serve.

Now the ball, on a twist serve, may very well deform a bit differently than it does on other types of serve. However, this is not really the underlying cause of the way bounces. The ball bounces the way it dues because of the way the ball interacts (rolls/skid/etc) with the ground. This interaction is influenced by the speed, the spins and trajectory on the ball prior to the bounce.

Note that (vertical-axis) sidespin does not directly affect the bounce (height or direction) according to physicist, Rod Cross. OTOH, horizontal-axis spins do have an effect on bounce height and direction. The most common of these is topspin and underspin. A ball that bounces off to the left or right, relative to the pre-bounce direction, indicates the presence of spiralspin as toly has indicated. This type of spin accounts for the left/right deviation seen on the bounce of a twist serve.

I've been talking about spiral spin for 4-5 years in these forums -- there are quite a few threads that discuss this type of spin. In his book, Technical Tennis, physicist Rod Cross refers to it as spiralspin, However, in his TWU article on kick serves, Rod refers it as gyrospin. It is sometimes aka Z-axis spin or longitudinal spin. Table tennis players refer to this spin type as corkscrew spin (or corkspin).

21. jwbarrientosHall of Fame

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The follow thru at 8:12:56 and contact point at 8:12:66 ... that's why I never could make my twist serve work

22. mightyrickLegend

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You make an important point about the need for clarification. I think that most times, when people say "kick serve", they generally just mean any serve that has a significant topspin component which causes the ball to accelerate downards with an ever steepening angle of attack -- due to the magnus effect. The downwards acceleration causes a significant bounce. Hence, "kick".

If someone is talking about a kick serve with a significant corkspin component, then this is obviously a twist serve where the resulting ball will also bounce in the direction of the corkspin.

For me, I find that a twist serve feels VERY different than a standard non-twist kick serve. For a twist, I will usually toss at least six inches behind my head. I find it makes it much more difficult to generate pace and get leverage. So these serves are usually much slower than a topspin or top/slice. But the resulting bounce outwards is usually rewarding.

23. tolyHall of Fame

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Thank you so much. I corrected the picture, so you have no excuse and should hit perfect twist serve.

24. jmnkProfessional

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so essentially you are saying that on twist serve one hits the ball downward? I thought someone was claiming that unless you are like 7' tall you can't really hit the serve downward and expect it to land in the service box?

25. SystemicAnomalyG.O.A.T.

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^ A 6'9" player who jumps should also be able to hit down on the ball.

Not sure that toly is actually saying that most players will be hittng downward on the ball. He does say that the racket face is slightly closed and the contact point is above the equator of the ball. However, if you look closely at his picture from the OP, it appears to indicate that the racket head is still moving upward at/after contact. The tip of the racket is higher in position 3 than it is at position 2 (the instant when the ball is contacted). There is still an upward brush on the ball -- (the contact lasts a mere 4-5 ms).

Last edited: Sep 20, 2012
26. jmnkProfessional

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It's not physically possible to hit a sphere (a ball) with forward tilted plane (a racket) above the equator of the sphere, and --not-- hit down on the sphere.

saying 'the racket face is slightly closed and the contact point is above the equator of the ball.' and saying 'hitting down on the ball' means exactly the same.

27. SystemicAnomalyG.O.A.T.

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This sounds like a matter of semantics. To my mind, and I suspect to most people, if you say that you are hitting down on the ball, it implies that the racket face is closed and moving in a downward direction at impact. In the case of the serve (and most topspin g'strokes hit with a slightly closed face), the racket is not moving in a downward direction at all but is moving upward during the contact phase.

In fact, in studying slow motion videos of serves/shots hit with a slightly close face in the manner I described, the ball moves upward just after contact, not down. Take a look at the link below about 30 seconds in. This, to me, is a clear indication that we are not hitting down on the ball.

.

Last edited: Sep 20, 2012
28. tolyHall of Fame

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I hope the following pictures can resolve this dispute.

Figure 6. Arm and racquet motions around contact

The fig.6 demonstrates that tip of the racquet moves upward and to the right. The frame #4 is contact point. The arm pronation, wrist flexion, arm and body forward rotation move the racquet to the right and create flat component VF of the racquet velocity VR, see fig.7. The wrist ulnar deviation and elbow flexion move the racquet upward and produce topspin component VTopspin. I ignored horizontal spins, because they are not essential here.

Figure 7. Ball’s trajectory after impact

So, velocity of the racquet VR is facing up and to the right, not downward. The flat component VF is directed downward and to the right.

However, why the direction of the ball VB does not coincide with racquet velocity direction VR? The fact is that some of the energy of VTopspin is spent on topspin production.

Last edited: Oct 1, 2012
29. SystemicAnomalyG.O.A.T.

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^ Not sure that your additional images resolve all the issues. It clearly shows that the racket is travelling upward before and after contact. However, in this case, the ball the ball appears to be falling (at a slower rate than the toss) after contact. Did this serve go over the net? Was the server jumping and how tall is he?

Quite a few slow-motion videos, such as the one I posted above, show that the racket face appears to be slightly closed yet the ball rises for a while after contact before falling. There may very well be some cases where the ball is still falling slightly just after contact (such as a with a very tall server who is jumping). OTOH, many videos show the ball rising. A single case is not necessarily representative of most serves.
.

Last edited: Sep 20, 2012
30. tolyHall of Fame

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There are two more examples of the ball direction.

Figure 7. Direction of the balls around contact

Again, the balls move downward.

Videos don’t show server jumps and balls near the net.

IMO, in case of Twist serve ball usually isn’t rising, but I’m not sure.

31. SystemicAnomalyG.O.A.T.

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^ The video I posted and others clearly show the ball rising. When I hit my twist and other kick serves, the ball is also rising just after contact -- definitely more than my flat serve. (BTW, I am 5'10" and probably jump about 10 cm or so on my serves).

.

Last edited: Sep 21, 2012
32. jmnkProfessional

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the only way you can make the stationary ball raise is to hit it below the equator. (I mean that is assuming we disregard the effect of the friction between the strings and the ball. I suppose when friction is considered it could be argued that the ball could be hit above the equator and still pulled up - but I would be surprised if that was in any way significant).
Which is why the tip about hitting from 8 to 2 makes sense (at least to me). But when one says that the contact does not start until around 10, which is above the equator, I just do not see how it would make the ball raise.
Note, that forehand stroke of the incoming ball, the one that is raising and spinning is different than a serve. There's a pretty good article on all of that on TW University (or few papers by Broody).
What you see on the video is someone hitting below the equator. And it is really hard to see where the initial impact happens so sometimes it looks like it is around 10.
But you make a good observation - the ball does raise most of the time. Just look at any of those drills where people serve from their knees, and the ball goes up really high over the net. It is because they hit it below the equator.

33. charliefederererLegend

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Got to agree with SA that the racquet is moving up for twist and kick serves, and that the ball initially rises, even if the racquet face is slightly closed.

Here is a sequence of Sam Stosur serving that Toly had previously posted:

One could argue exactly which pic ball contact occurs at. My reading is that ball contact occurs at pic 19, but certainly by pic 20 at the latest.

Clearly on pic 25 the ball is off the racquet. But in this pic, notice that the ball is definitely lower than the top of the "25" stamped into the upper corner of this pic.

Now look at pic 26 where the ball is almost even with the top of the "26" stamped into the upper corner.

Then on pics 27 and 28 the ball is higher still!

That ball is rising!

Last edited: Sep 21, 2012
34. tolyHall of Fame

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Here is a sequence of pro flat serve.

Figure 8. Flat serve

During impact, frame #3 and #4, the racquet moves downward. The racquet doesn’t move up due to the wrist ulnar deviation is locked. So, there is no topspin at all and just a little sidespin. To produce this kind of racquet swing the hand/wrist muscles must be active.

Last edited: Oct 22, 2012
35. tolyHall of Fame

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I checked a lot of videos of different serves and different players. I failed to find any serve with rising ball.

Your examples are optical illusions. :shock:

36. LeeDBionic Poster

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I am far from pro.
When I hit a twist serve, the ball rises off it's strikepoint, which is around 8'6" or so. For flat serves, I think my ball goes flat out, from a strikepoint around 9'4".

37. NetspiritHall of Fame

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In a twist serve, the ball obviously rises. You cannot clear the net with a completely flat or descending trajectory regardless of what serve you hit, if you are not as tall as Karlovic.

You must hit UP. The point of contact is below the balls "equator" and on the left side (for righties). This is why it is thrown behind the head and to the left - to be able to brush up on the left side of the ball.

38. tolyHall of Fame

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Rod Cross disagrees with you. See please his article – Physics of the Tennis Kick Serve in http://twu.tennis-warehouse.com/learning_center/kickserve.php.

I made the picture from his video.

Figure 9. Slice serve - Rod Cross

Try please to find a similar video that could support your statements.

Last edited: Sep 23, 2012
39. NetspiritHall of Fame

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They explain it like this: "Even though the ball is struck while the head is rising, the ball travels downward toward the net because of the high ball toss and rotation of the racquet during the impact. The high ball toss means that the ball drops rapidly both before and after the impact."

I am not convinced that a high ball toss and downward ball motion is the only way to produce a twist serve, or even the best way. The ones I have seen (and attempted myself) had quite a lot of kick/topspin on them and curved up-and-down.

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41. SystemicAnomalyG.O.A.T.

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Take another look at the video above. Note the position of the ball at contact with respect to the top of the frame at the 0:33 mark. After the ball has left the racquet, it moves upward out of the frame. The camera position does not move. How is this an illusion? If you can't find other examples, you just are not looking hard enough.

Not so sure that the image sequence from CharlieF is an optical illusion either. It's hard to say for sure. The camera position/perspective does not change. The ball appears to rising in this example. If anything, this camera perspective tends to disguise/minimize the amount that the ball is rising. If this was shot at an angle that is parallel to the court and close to the height of the contact, we would see that the ball actually rises more than this sequence of images would seem to indicate.

Granted, there are probably plenty of players who can hit a flat serve such that the ball starts to drop as soon as it leaves the racket. It may be something of a myth that the server must be 6'9" (206 cm) or taller to accomplish this. However, probably only a very small percentage of players can hit a twist or other kick serve that does not rise when leaving the racquet.

Your example that shows a twist serve, hit with a closed racquet face, with the ball falling as it leaves the racquet does not apply to most servers. For a kick/twist serve, I am not sure if it is possible to hit the ball with a closed face and have the ball rise. Many players may actually hit it with a neutral face or one that is somewhat open.

In his TWU article, Rod Cross claims that a kick serve must be hit at about 100 mph. This is not a requirement for hitting for hitting a kick serve at all. Most servers hit their kick serves well under 90 mph (even well under 80 mph). Clearly, the kick serve that he speaks of is one that very few players can actually hit. Rod later amended his stance on this and admitted the kick serves did not need to bit hit close to 100 mph.

Take a gander at the following video from Pat Dougherty (the "Serve Doctor"), who is a serving guru with the Bolletierri Tennis Academy. At the 1:24 mark in the video he says the ball must first go up and then come down sharply for an effective "sick kick".

.

Last edited: Sep 22, 2012
42. LeeDBionic Poster

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Rod guy is fooling himself.
That racket is vertical. That is NOT a twist serve. A twist serve, the rackethead is accelerating upwards, and a vertical racket has already done that. Like a topspin forehand, look at the angle of the racket as it contacts the ball. It's almost vertical, yes, but still RISING as it contacts the ball. That is what gives the ball it's topspin, like a topspin forehand.

43. tolyHall of Fame

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Let's look at the next photos of Stosur kick serves.

Figure 10. Sam Stosur Kick Serve

Unfortunately every picture produces an illusion. Nevertheless, it seems that the ball falls after contact even in case of kick serve. IMO there is no way it rises in case of twist serve.

Last edited: Sep 24, 2012
44. NetspiritHall of Fame

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I guess it is possible for a ball to go slightly downwards. If the pace is significant, it may be able to clear the net before it descends too much, and if the spin is significant, it may curve into the service box.

I definitely cannot serve like this - it probably requires a huge jump, racket head speed and arm extension. Recreational folks would be better off trying to hit twist serves by brushing up the left side of the ball, not down the right side.

45. tolyHall of Fame

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Even leeD can hit twist serve around 100mph. There should be no problem for you.

Here is nice video of Marco Chiudinelli Twist (or Kick?) serve - http://www.youtube.com/watch?v=b8RGuB1Wj_E.

I copied few frames from this video. Again optical illusion, it gives the impression the racquet moves faster than ball.:shock:

Figure 11. Marco Chiudinelli Twist Serve

Last edited: Sep 25, 2012
46. zapvorG.O.A.T.

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that is whats happenening, but thats not the cause. its from teh spin you put on the ball from hitting it a certain way

47. SystemicAnomalyG.O.A.T.

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I noticed that you ignored the original link that I provided that showed a rising ball on a kick serve. I know with absolute certainty that nearly every kick serve that I have hit for the past 20+ years has risen after contact. Many other serves that I have faced (4.0 to 5.5 level players) have a kick or twist serve that rises noticeably after contact. With a small % of these servers, it is not apparent if the ball rises or not.

Even Rod Cross talks about kick serves that rise (the "lob" kick serve he mentions is an example of this).
.

Last edited: Sep 24, 2012
48. jmnkProfessional

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@toly and @SystemicAnomaly - I think you are--both-- right, in a sense.

a) it is certainly possible to hit a twist (or a kick) serve that initially raises. This happens when the contact point, at least initially, is below the ball equator.

b) it is also possible to hit a twist (or a kick) serve that does not raise at all, but from the very beginning goes a bit downward. This happens when the contact point is above the ball equator.

for most of rec players it is certainly easier to do a). Pros can do b) as they can hit the ball so hard, and while jumping, that it will go over the net even though the trajectory is downward from the beginning.

What is not possible is to hit the ball above the equator (like from 10 to 2) and expect the ball to raise.

49. tolyHall of Fame

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I’m not ready to discuss optical distortion (maybe Chas Tennis can), that’s why I ignored your original link.

Agreed, before this thread I thought the ball always rises after impact. It’s absolutely unbelievable pros can and practically constantly hit downward. :shock:

Last edited: Sep 24, 2012
50. tolyHall of Fame

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Here is Chiudinelli twist serve entire trajectory of the ball.

Figure 12. Twist serve - complete ball’s path