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Table Tennis Topspin/Chop questions

  1. Jan 20, 2008 #1
    1. When someone loops, and the person blocks, the ball goes out...if the ball really rides up the rubber, shouldn't it have backspin when it comes back? Since friction accelerates the spin. For instance, when I sidespin, the ball I get back is the continual motion of the ball, instead of its opposite due to angular rebound...am I being clear?

    2. Why does looping on a chop is more spinny than looping on a loop? In my head, the rebound speed should be just as much as additional speed.

    3. Which is a better chop/topspin, horizontal ways, or vertical ways? I know they are the same amount of spin, but which is harder to return...for instance, which chop runs to the net more...meaning harder to loop?

    :cool:
     
  2. jcsd
  3. Jan 21, 2008 #2

    Shooting Star

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    1. When your opponent has looped or put a top-spin, the ball is spinning such that the top of the ball is moving in the dircn of motion. When it hits your racquet, the pt of contact is moving down, and so rebounds up due to friction and elasticity.

    2. Looping on a chop enhances the spin. You are trying to rotate the ball in the dircn of the existing spin.

    3. Depends on your skill level. If you are a beginner, chop against a chop. If possible loop against a loop, but looping over a top spin is hard, so you have to jab it at a downward angle and just block it, so that it remains on the board. The spinnier chop will run to the net more, so you have to chop back really hard, and just clear the net.

    Smash ‘em hard!
     
  4. Jan 21, 2008 #3

    rcgldr

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    This depends on the elasticity and grip of the table tennis rubber. An typical offensive type rubber will have a lot of both, so the tendency is to reverse the spin, returning top spin against top spin, and back spin against back spin. This spin reflection tendency is more prevalent in certain rubbers, like Mark V. There are defensive rubbers with little grip or elasticity, will only slow the spin a little, returning backspin against top spin, and with little speed, but these type of rubbers aren't used by world class players.

    There's only so much spin a rubber can generate, because deformation will reach a limit. The main difference is the speed of the ball, looping against a chop will result in slower speed, than looping against a loop, will result in more speed and generaly has to be done away from the table. The spin in both cases isn't much different.

    Depends if you're talking about top world level players or average players. There aren't any choppers in the top 10, maybe one or two in the top 50, and these "choppers" have to be able to attack when there is an opportunity. Choppers are too far away from the table for sidespin to be of any use. Pure topspin is probably the hardest to return in terms of required racket angle, but sidespin used to curve the ball away from the table makes it harder to reach the ball in time for a clean shot. On a serve, a lot of sidespin will mask the amount of backspin or topspin on a ball.
     
  5. Jan 23, 2008 #4
    Actually, if you are doing a pure loop, the ball no matter how much it spins, realistically, will never have so much spin that it will pass beyond the point of elasticity for the sponge. B/c pure loop involves brushing the blade right on top of the ball by friction of the rubber, that way, only the spin part of the ball sinks in the sponge....which is not a lot.

    I also started the same post on another forum, they even drew out diagrams, not as smart though, but very passionate(its a table tennis forum), and according to them, topspin on a topspin generates more spin than topspin on a backspin....here, check this out.

    http://tabletennis.gr/forum/forum_posts.asp?TID=9807&SID=a9z5e9545d3478614e1ad2bz7833fd4f

    The discussions have gotten quite long, so I'll give you a little help to sort it out.....the discussion for this question begins my SIDOFMILENIUM's 2nd post, the first reply is given w/ first diagram on the page which is easy to locate as you scroll down.

    Hope you agree, coz othervise, I gotta rebuilt my head.
     
  6. Jan 23, 2008 #5

    rcgldr

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    The more the rubber is deformed, the less energy is conserved during the impact, although the amount of loss doesn't significantly decrease until the rubber is stretched quite a bit.

    Eventually you reach a practical limit for how much the rubber can change the spin on the ball, especially if there is significant slippage during the initial and final period of contact with the rubber when the normal force is very small. If the blade speed is fast enough, it's possible that looping against backspin will have the same or even more spin than looping against top spin. A lower blade speeds, the opposite is true, more top spin against top spin than against back spin.
     
  7. Jan 23, 2008 #6
    Wait a second, how is it possible on fast blade to loop against a backspin and create more spin?
     
  8. Jan 24, 2008 #7

    rcgldr

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    This would only happen at extremely fast blade speeds, like a loop - kill shot but with grazing contact. The combination of the pre-impact spin, the very fast blade speed, the relatively shorter impact time, and the maximum amount of energy retension in the rubber and sponge limit the reversal of the spin.

    What I've seen is that with high blade speed, the return speed will be much higher against top spin than back spin, but the spin will be close or a littler more against backspin. This is based on observation of how much the ball curves.

    However, there's another possible explanation. Normally, a table tennis ball never moves fast enough to experience severe turbulent air flow, but at very high speeds, the turbulent air flow could be enough to reduce the curve reaction of the ball as it travels.

    Obviously with enough blade speed, the limits of the rubber can be exceeded, but I'm not sure if it's humanly possible to generate that much blade speed.
     
  9. Jan 24, 2008 #8
    the main factor here is that ping pong balls are really light weight, so the impulse created is very small. So most of the time the spin on the ball will be about the same whether you hit it already spinning or from stationary. However the angle it leaves the bat does change quite significantly. If someone does a really powerful backspin shot, the best way to get it back is to do the exact same shot with the bat angled backwards, this reverses the spin and so will cancel out the effect of the spin.

    If you try to top spin a back spin shot, then it will nearly always go into the net due to the angle of your bat and the effect of the backspin, so you have to hit it upwards much more as the backsipn makes it want to travel into the net.

    So the rules are;
    1. to return a backspin shot with backspin, hit it back with the same amount of backspin, as it cancels the spin.
    2. to return a backspin shot with topspin, aim a lot higher than usual and with more topspin
    3. to return a topspin shot with topspin, hit it with the same amount of top as they did to cancel the spin.
    4. to return a topspin shot with backspin, aim much lower than usual and with more backspin

    And the best type of spin to put on is sidespin, as the opponent always has to think about which side the spin is going to make the ball go. Especially when serving, and especially if you can hide the direction you hit it by shielding it behind your shoulder like I used to do. Most players dont use sidespin in games as it takes longer to do the shot and table tennis is a very quick game at pro level, pro's usually stick to top and backspin.
    When it is a backspin or topspin, it is easy to work out, you apply the same spin as them to make it easy, or if your being adventurous you can alternate it, but this requires you adjust where you hit the ball quite severely.

    I think thats wrong. It may feel as if you are generating more spin when you hit it, but that is because you are putting more force in to change the spin of the ball back the other way. When its a slice shot onto a topspin you are effectively re-enforcing the spin already on the ball.

    Saying all that, it depends on what your bat is like. The one I used to use in tournaments cost about $250 (yes, rip off :smile:) as it had amazingly sticky grip and the ball would never slide across the surface. But some people choose to use bats with no grip at all, so the spin deosn't effect them as much. So it totally depends on the 'stickyness' of your bat really.

    THIS table tennis match is a perfect example of how to alternate top spin to back spin and back. One person is brilliant at top spin, the other at back spin. And i mean really brilliant, one of the best ping pong rallys i've seen.
     
    Last edited: Jan 24, 2008
  10. Sep 5, 2008 #9
    wrong
    consider 2 identical robots infinitely playing identical backspin strokes to each other (1st stroke struck from hand)
    consider ball/bat impact speed which will effect the spin
    1st chop has impact speed consistent with stroke effort x + zero rotational force from ball
    2nd chop has impact speed consistent with stroke effort x + y (Speed of ball surface rotating toward racket)
    and so on
    The backspin will be greater for each succeeding shot, necessitating the racket angle to be increasingly opened to avoid landing in net
    true, but not so interesting
    wrong see above for backspin
    The topspin will be greater for each succeeding shot, necessitating the racket angle to be increasingly closed to avoid going long

    true, but not so interesting

    brush up on the physics guys!
     
  11. Sep 5, 2008 #10

    rcgldr

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    Even if table tennis rubber were 100% elastic (no losses), aerodynamic friction and drag would put an upper limit on the spin and speed developed from stikes made at the same speed. Since the rubber itself also involves losses, the ball reaches it's upper limit sooner.

    I made a short video to show the grip and elasticity of table tennis rubber. In the later part of the clip, I alternate the spin on the ball while causing the ball to bounce upwards using a somewhat short stroke. I could hit the ball higher and with more spin, the the result is about the same, after about 2 or 3 strikes, the motion stablizes.

    http://jeffareid.net/real/ttstick.wmv

    youtube version (if web site is down):
    http://www.youtube.com/v/hWn08zsLZQw&fmt=18
     
    Last edited: Sep 5, 2008
  12. Sep 7, 2008 #11
    though yr 2nd clip illustrates well what we are talking about your suggestion that it shows the amount of spin generated as stabilising after 3 reps as a bit subjective. Yr ball striking is not near enough to a pure brushing motion to be a good test. In an (equally subjective i admit) practice session with another player I found that I could reach six strokes of topspin, before losing control. Then the need to close the racket and stroke closer to the horizontal meant one of us would make an error. My partner was a former uk top 100 player a big help when trying something like this. I am sure international level player could do better.
    From a tt perspective the key thing is that as the arc and spin escalate precision of contact becomes more important than physical strength
     
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