Pronation versus "wrist snap"...

Discussion in 'Tennis Tips/Instruction' started by gzhpcu, Mar 22, 2009.

  1. Kevo

    Kevo Hall of Fame

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    I think the idea of wrist "snap" has too many different interpretations to be all that useful in general. However, I can see why some people would use the term.

    My best serves are the ones where I really delay the wrist action as long as possible. The later it comes into the swing the faster the racquet comes around.

    I think that they delaying and loading of the wrist before contact can be a conscious thing. That last minute "snap" into the ball where you release the wrist and accelerate it into contact is what I think is meant by snap, at least by people who are actually using pronation and not so much flexion.

    The tricky part for me is the timing. I found that it works best if I have finished the snap and have "let go" or relaxed my arm right at contact. It totally gets messed up if I am still trying to actively use muscles at contact.

    I think you could imagine it as a playground swing. You have to push in harmony with the motion or you end up reducing speed.
     
    #51
  2. sureshs

    sureshs Bionic Poster

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    At what level is it essential? What about the usual recreational club crowd?

    Isn't it more like pronation is essential only for hitting a flat serve with a continental grip but a good thing to have in general?
     
    #52
  3. JediMindTrick

    JediMindTrick Professional

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    All the pro serve videos show that the wrist is not flexed after contact so there is no wrist snap.
     
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  4. sureshs

    sureshs Bionic Poster

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    Not if you are hitting a slice or topspin serve.

    But I see what you are saying. It is not an abrupt snap at the end (just before impact) but a slight drooping of the wrist during the forward swing.

    Pronation would be turning the wrist so that the palm faces the other way.

    That is why I don't think they are the same at all.

    The many videos on the web that feature coaches teaching a wrist snap often show a drill - stand still and get a fast serve in by a wrist snap. In a real serve, this exaggerated snap is replaced by a smoother downward wrist motion.

    The snap seems to be needed for intermediate-height players. Really short dudes can hit in front and the ball will land in due to the geometry. Really tall guys can hit down on the ball at impact and get it into the court. There seems to be some height range where the ball needs to be consciously pulled into the service box.
     
    #54
  5. JediMindTrick

    JediMindTrick Professional

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    Again with hitting down on the ball?
     
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  6. drakulie

    drakulie Talk Tennis Guru

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    Not one player I have shot photos and/or high speed video of, from recreational to pro have I captured a shot of them hitting down on the ball. The racquet face is almost always perfetly perpendicular to the ground. This is even more evident on the lower level players, where they don't get as much height. Many of them, actually have the racquet face open at contact, yet they still get the ball in play.


    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]
     
    #56
  7. JediMindTrick

    JediMindTrick Professional

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    No matter how many threads we have about the "wrist snap", this thing is never going to die, 10 years from now the controversy will rage on.
     
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  8. gzhpcu

    gzhpcu Professional

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    What is termed "wrist snap" is not just extension and flexion.

    It is extension, then a combination of ulnar deviation and flexion. Try the combination and you will see that when you ulnar deviation, the flexing is much more restricted. Ulnar deviation can be as much as 30 degrees. This is why you do not see the wrist really flexing forward after impact on the serve.

    It is only when you hit a smash with the ball behind your head that you do pure extension and flexion.

    Quoting from Training for Tennis, page 72:
    http://www.pponline.co.uk/workbook/wsstw/2334479/tennis.pdf

     
    #58
  9. gzhpcu

    gzhpcu Professional

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    The controversy probably rages on, because people understand different wrist movements under "wrist snap". As I mentioned, it is not simply extension-flexion of the wrist.
     
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  10. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    The club crowd should be using pronation. It should be used for all serves -- it just that it is more obvious, more pronounced with flatter serves.
     
    #60
  11. JediMindTrick

    JediMindTrick Professional

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    It's not that simple, because the "loose wrist" camp says that you shouldn't do anything with your wrist, I mean anything at all, no flexion, no snap, no ulnar deviation, no pronation (yes no pronation, because pronation is a movement of the forearm not of the wrist), no nothing. The only thing you should do is keep the wrist as loose as posible, idealy it should be so loose that if you were to swing and miss the ball, the racquet would fly out of your hand, like it happened to the Djoker. As soon as you try to "snap the wrist" you will tighten the wrist and lose power.

    Oh and pronate the forearm, not the wrist. Personally, I think you should also pronate the upper arm.
     
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  12. gzhpcu

    gzhpcu Professional

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    Here is another article, Where do High Speed Serves Come From? (sports science information for coaches/Guillermo Noffal - California State University, Fullerton, USA)

     
    #62
  13. sureshs

    sureshs Bionic Poster

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    I have shown you numerous photos (taken by you) where they are hitting down at impact. Not everyone does it every time of course. You are just being selective. I have traced the perpendicular to the string face at impact and shown that it points below the horizontal. I even pointed that out in the Murray serve analyzed by Tennis mag in a series of photos.
     
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  14. JediMindTrick

    JediMindTrick Professional

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    It doesn't even matter where the racquet head points at impact, what matters is how the racquet head moves at impact, and it should move up because that's the only way to get topspin, if it moves down you get underspin. Of course there is also a sideway component but on the vertical axis the racquet head should move up.
     
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  15. Kaptain Karl

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    I've avoided most of the Wrist Snap threads because nobody seems to agree on a definition of terms in the first place. But ... when I think "wrist snap" I'm really thinking "ulnar deviation." The only time I see players trying to use flexion in their Service Motions ... they stink. (Not the players; their serves.)

    Another "But" ... when teaching I *say* "snap" and demonstrate both ulnar deviation and pronation. (I just avoid using the technical terminology because most MS and HS kids don't understand them.)




    We might be conceptualizing the same thing from different angles, but I say "snap" has too many different interpretations to be all that useful in specificity.

    Good word picture...!




    Bingo!!! (suresh, have you ever noticed pics of Federer's (Nadal's, Djoker's) forehand at impact with the ball? Many times the face is closed, but the ball isn't going into the net. Same with the Serve. The face may be "angled" down, but the racket head speed and swing path more than compensate for that.) Even Karlovic is hitting UP on the ball when serving....

    - KK
     
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  16. Lsmkenpo

    Lsmkenpo Hall of Fame

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    Consciously attempting to snap the wrist on serve is a mistake and just adds inconsistency to the serve IMO. Wrist release is a better term to use and will occur naturally in the kinetic chain of the serve if your motion remains fluid and relaxed, relaxation is the key.

    Pronation is more of a result of using a proper service motion keeping your racquet on edge upward until impact, if your motion is correct you will pronate at the top of your serve, shouldn't be forced.
     
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  17. drakulie

    drakulie Talk Tennis Guru

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    Oh, yes. You are correct. You did show me some of the photos taken by me, where they are hitting "down on the ball". Here is one of the photos you referred to:

    [​IMG]
     
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  18. gzhpcu

    gzhpcu Professional

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    If I can sum up the discussion so far:
    • Under the term "wrist snap" persons understand different things
    • Various Bbiomechanical studies have shown that wrist extension, ulnar deviation and flexion play a big role in the serve
    • When the wrist ulnar deviates at the same time as it flexes at impact, the resulting flexion is reduced
    • Keeping the arm loose will result in wrist movement
    • The point where no agreement is reached, is whether or not a conscious wrist ulnar deviation/flexion at impact is needed to accentuate the wrist movement (Bruce Elliot seems to think so in his study, some in this thread do also, others here do not)), so if it works for you do it
     
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  19. nousername

    nousername Rookie

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    gotta be VERY careful with these pictures:

    consider:

    1) What kind of camera was used? what this a good SLR/dSLR camera? if so, it has a focal-plane mechanical shutter, with which comes distortion of things in motion. the shutter usually slides down to expose the film/sensor. which means that the top of the photo is expose at an earlier time than the bottom of the photo. that is what make the racket look bent in the above picture, and the illusion that it is facing up.
    - here is PROOF that the racket "bend" is from camera mechanical focal plane exposure and not from impact forces: the ball in the pics is crystal clear AND the string bed is not stretched, thus the ball has NOT been hit yet --> thus we know there are no forces on the racket yet --> thus, if no forces then the racket is NOT actually bent.

    2) the important "racket angle" is the angle of the racket just at the ball LEAVES the stringbed. all you your photos are just before or at contact, so even if you could get an "undistorted" photo, the important ones are the ones just as the ball is leaving the racket.

    these are just FYI, i'm not disagreeing or agreeing with you. BUT here is a recent post from me about "hitting up" on the serve, that may shed some light on this matter: difference in attitude and velocity
     
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  20. drakulie

    drakulie Talk Tennis Guru

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    Actually, this is incorrect. Racquets do bend as they are being swung with no impact from a ball. The head of the frame lags behind the grip, thus creating a bend/arch. Frames are not steel, they are made of materials that are strong enough to bend, and not break.

    Same thing as when you get a branch from a tree, and use it as a whip. You could swing it very slowly and see it arching while you are swinging it.

    BTW, camera used is a Casio Ex-F1. This particular shot was from a series of 6o fps photos. The racquet is absolutely bending in the air.

    I have other sequences where one can see the frame bent, before, during, and after impact.

    here are a few that are at impact, and you could clearly see the frame bent.

     
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  21. gzhpcu

    gzhpcu Professional

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    The top of the racket must bend back (recoil) at impact, otherwise the racket would be incredibly stiff and hurt your arm. Just test it by putting the racket down on a table so that the head is in the air and press down on it. All rackets have a certain amount of flex.
     
    #71
  22. drakulie

    drakulie Talk Tennis Guru

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    ^^Exactly, and the faster one swings it, the more the "mass" in the head of the frame weighs, resulting in bend, even without impact with the ball.
     
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  23. nousername

    nousername Rookie

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    hey drakulie, not to be argumentative, but you proved my point even more. the effect is even WORSE with CMOS based video cameras.

    don't take my word for it, but this website has tons of videos and proof:
    http://dvxuser.com/jason/CMOS-CCD/

    there's some good stuff here too about "camera wobble":
    http://www.luminous-landscape.com/reviews/cameras/d90.shtml

    here's a great shot of skew/wobble (skew is the term for single frame images, "wobble" is the skew effect in video):
    http://en.wikipedia.org/wiki/File:Focalplane_shutter_distortions.jpg

    is that convincing enough?

    (FYI, FPS is not the driver, it is the shutter speed, and the top-down shutter mechanism.)

    lastly, you are just flat out wrong about bending the racket bending in air. of course if you have a limp whip or lightweight stick sure it will bend when you swing it!! but a stiff racket? nope. the distortion on a racket even during ATP Touring PRO full-force shot is smaller than you realize. you need REALLY fast vid to see this 60 fps is no where close enough. you need that awesome 1000 fps stuff they show.

    all your "bent" frame pics are due to "camera wobble". that's it. all your pics are extremely consistent with the camera wobble effect:
    1) it is induced be side-ways motion
    2) results in what looks like a vertical tilt
    3) top-down shutter exposure: top of the picture exposed first, followed later by exposing the bottom.

    the skews in your pictures fit that effect perfectly with the described effect.
     
    Last edited: Mar 25, 2009
    #73
  24. nousername

    nousername Rookie

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    of course the racket bends back at impact, but there isn't much force on it during the swing. the distorting forces during the swing are NEGLIGIBLE compared to the forces at impact. i'm sure there's some references out there one this.

    to gzhpcu, don't you think the strings are soft enough to absorb the impact? the strings are FAR less stiff than the racket frame. those old grandma racket are EXTREMELY stiff, they have almost no flex. some people love 'em and have no arm problems. you know those frames i'm talking about ... they have head sizes the size of watermelons and frames 2 inches thick, but light as a feather.
     
    Last edited: Mar 25, 2009
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  25. gzhpcu

    gzhpcu Professional

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    Yes, certainly the strings are a lot more elastic by comparision. I agree.

    The type of racket you mention is for persons who are beginners or eternal hackers who do not have a proper full swing and just swat at the ball. They usually also have low string tension to enlarge the sweet spot even more, and provide a trampoline effect.
     
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  26. nousername

    nousername Rookie

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    right ... i guess i was confused by your comments ... not sure if you agree with me or with drakulie ... but i'm am convinced there is negligible racket distortion during the swing. all and any distortion is due to impact. all the distortion in drakulie pics are 100% (ok, well, 99.9%) camera skew/wobble.
     
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  27. gzhpcu

    gzhpcu Professional

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    I agree with you in that I also do not believe there is any racket distortion during the swing prior to contact.
     
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  28. gzhpcu

    gzhpcu Professional

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    Thinking things over as a result of this discussion, I am now pretty much convinced, that while there is substantial wrist movement on the serve, it is not consciously willed prior to impact.

    Discussing these issues with a friend of mine, an Argentine teaching pro, who played ATP futures and challenger tournaments, we came to this type of a conclusion:

    To get the right technique, a three pronged approach is needed:

    • images: watch slow motion videos of the type of stroke you are attempting to achieve, this is the visual tennis technique of John Yandell
    • feeling: when you ape the movement you want to achieve based on the images, note how it feels, then check during play if you have the same feeling
    • thinking: think about doing a certain movement (for example, the wrist movement at impact we have been discussing) prior to playing, but not while actually executing the shot. Willing it in your mind, is another step towards actually doing it

    Lastly, be patient, but remember, it is always possible to change your technique
     
    #78
  29. gzhpcu

    gzhpcu Professional

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    Yes, and, in addition there is another effect:

    source: http://www.jstage.jst.go.jp/article/ijshs/5/0/157/_pdf
     
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  30. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    #80
  31. larry10s

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    i give kudos to erveryone who participated in this very intellectual non derogatory or sarcastic discussion of an important topic. gzh pcu thanks for summarizing the salient points will be helpful to reference. maybe you could do the same for the other serve posts you hosted.
     
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  32. drakulie

    drakulie Talk Tennis Guru

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    nousername, when I responded to you, I was talking about the effects of a swing on a frame, and not the camera. Frames **DO** bend, even when they have not made contact with anything. Frames are made of strong materials that are able to bend and not break. A serve going 100 mph, needs to have the racquet head speeding at I believe close to 130 mph. That is **A LOT** of force, and the air causes drag and resistance, which again effects the frame bending.

    As for he camera, I don't know enough to discuss. However, a few things to consider.

    1. If it is the camera that is resulting in this "wobble/bend/warp" effect, then why isn't it effecting the hand and/or arm on any of the photos?? Are you suggesting the camera some how knows that it should only create this effect and only limit it to the frame head???

    2. Where does the effect of the shutter start and end on the image?? You spoke about it first capturing the top half, then bottom half, etc of the image. Again, does the camera's shutter know it is only suppose to limit this effect to wherever the racquet head is going to be i the image?? (ie: top half, bottom half, right side, left side, etc)

    Just things to consider.

    As for the topic, and the point someone made about where is the frame **after** impact, it is surely not pointing down. In many images it is still perpendicular and moving up, or forward. It takes quite a while before one sees the frame beginning to point down. (ball not even in photo sequence any more)

    Again, interesting discussion.
     
    #82
  33. sureshs

    sureshs Bionic Poster

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    And indeed hitting up is true for topspin and topspin-slice serves, and I had also mentioned that before, something which a certain poster selectively forgets. But I also found numerous cases where the frame was right on top of the ball and bearing down on it at impact. If the ball is hit on the side with a grazing impact, the racquet can be going up but its face pointed down - but not down into the top of the ball, only to the side. This happens for the classic second serve all the time. For more "flat" hits, the face must be drilling down into the ball if it is pointed down at impact. I don't how to dig it up with the right keywords, but I had pointed this out in a thread for photo after photo in a thread.

    The swing path is the issue here, as you point out. If the swing path is grazing the ball, it can be going up while delivering a "glancing blow" to the side while pointing down sideways. And the swing speed will impart sufficient force to make the ball move forward and not crash down towards where the face is pointing.

    But not when the impact is head on as viewed from the direction in which the ball eventually moves.
     
    #83
  34. JohnYandell

    JohnYandell Hall of Fame

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    Guys,

    On the rcket versus camera bend thing. I was shocked to see some of our footage a couple of years ago show the same effect. Turns out it really is something in the video processing. Can't explain it technically but our editor was able to redress it. Strange that it's just the racket but it is definitely an anomoly.

    If it was real, then you would certainly see it in the thousands of other clips on our site, and in the Utube high speed footage. In the super high speed footage you can see the frame wobble and react to the hit, but certainly not bow back in the kind of curve in those photos.
     
    #84
  35. sureshs

    sureshs Bionic Poster

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    So drakulie what is the conclusion? This came up in a previous thread too. Is the frame bending due to the flex like a whip? Did you try with unstrung frame to judge wind effect?

    I was thinking more about this and I think the "flex" is not human-perceptible in the sense that both the K90 and a RQIS1 Tour don't "bend" if you try to bend it. It is perceived as feel when hitting the ball of course. So I am wondering if even "flexy" frames are rigid enough, and to get the whip effect, they have to be swung at a speed not possible by humans.

    In other words, I also suspect camera blur now.
     
    #85
  36. sureshs

    sureshs Bionic Poster

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    The frame head has the highest linear velocity. As it is being swung, the points on the frame farthest from the pivot have the most velocity - hence subject to most blur.

    Again, as you say, 130 mph speed is not trivial (just read that now after my last post). So maybe ...
     
    Last edited: Mar 26, 2009
    #86
  37. gzhpcu

    gzhpcu Professional

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    OK, will attempt to do so. Thanks to everybody for the discussion. It changed my mind about conscious wrist action...:)
     
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  38. sureshs

    sureshs Bionic Poster

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    #88
  39. sureshs

    sureshs Bionic Poster

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    #89
  40. gzhpcu

    gzhpcu Professional

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    Can you please explain how Roddick puts topspin on the serve if his racket moves down prior to impact?

    source: http://tennis.about.com/od/playersmale/ss/roddickserve_8.htm

    It might be angled downward somewhat, but it is still moving up...
     
    #90
  41. Kevo

    Kevo Hall of Fame

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    His racquet can be pointing down slightly while still moving up and out away from his body. The ball is also struck off center more towards the top of the ball from the perspective of a person behind Andy.

    Spin can be initiated in multiple dimensions. Think about a pool stick putting spin on a cue ball. The stick can move only one direction, but put spin on the ball in a different direction by where it strikes the ball.

    In tennis, you can do a similar thing, by hitting the ball off center. On serve, you can swing in one direction and hit off center at the same time. It can get even more complicated since the racquet is not really in line with the arm when the ball is struck.
     
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  42. gzhpcu

    gzhpcu Professional

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    Agree. Key is that at impact, irregardless of the racket face angle, the racket has a vector component moving up...
     
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  43. sureshs

    sureshs Bionic Poster

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    1. I cannot explain anything - I just pointed out that in the video the highest point of the racquet head tip was reached before impact, and then the racquet moved down to impact. Between 0:35 and 0:36 you can even see the downward shift clearly.
    2. As I said, numerous times pros hit up on the ball to provide topspin, and then the face could point down but be moving up because the hit is grazing.

    1 and 2 are not contradictory. Both happen.
     
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  44. sureshs

    sureshs Bionic Poster

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    Yes it can happen and does happen many times. But sometimes it does not happen, as in the video.
     
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  45. gzhpcu

    gzhpcu Professional

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    If you think of it, the movement is extremely fast, so that a precise positioning of the racket head face is not possible. Therefore what you say happens...
     
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  46. J011yroger

    J011yroger G.O.A.T.

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    You have it backwards. Racquet head speed is lower than ballspeed.

    J
     
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  47. bad_call

    bad_call Legend

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    this would go along with F=ma. so glad i paid attention in high school physics.
     
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  48. sureshs

    sureshs Bionic Poster

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    That would be consistent with momentum transfer to a lighter object
     
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  49. J011yroger

    J011yroger G.O.A.T.

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    No need to explain to me, I enjoy, and understand physics.

    J
     
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  50. nousername

    nousername Rookie

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    good comments questions ... i'll do my best to answer them
    yes, i knew you were addressing the effect of swing on a frame. yes, frames do bend as a result of swing, BUT it is a tiny and negligible effect. it is so small it is not noticeable. the only time the bend in a noticeable amount it during contact, AND even then it is a very small amount. btw, every material on earth can bend and NOT break. even diamond, the hardest material earth can "bend". it is simply a matter of degree. there is nothing unique about the elastic properties of racket materials. so i agree with you on that. just b/c a racket is moving at 130mph does not mean there are forces on it. accelerations, not velocities, imply forces ... good ol' sir isaac proved that one: Force = mass * acceleration. you as a human can move at 18,000 mph and have 0 forces on your body ... don't ask me, just ask any astronaut.

    so .... for a serve and all other tennis shots, 99.9% of all the forces are due to IMPACT with the ball, not the swing.

    well, the truth is the effect IS in the whole photo. but the effect is proportional to velocity. at service contact, the main movement is the arm from shoulder to tip of racket. and the velocity is basically 0 at the shoulder and increasing towards the tip of the racket, where the max velocity is. that is why the bend is most pronounced at the tip of the racket, and is lessened as you go towards the shoulder.

    again, it effects the whole image. it's not top-half then bottom-half, it is simply "top to bottom". it's like a window that exposes a slit accross the sensor/film and that window slides down.

    and again, it affects mainly the racket head b/c the racket head is moving the fastest.


    yes, i understood why you were presenting you pictures, but due to these photographic effects they cannot be used to prove your point. in fact, they almost prove the opposite. b/c this "skew" effect tends to bend the frame backwards ... which gives the illusion/impression that the racket is angled straight or even upward. you really need a different camera to prove it either way.

    i believe the racket face is angled *slightly* downward when the ball is leaving the stringbed after a serve. AND that a "good" serve has upward racket velocity during contact.
     

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