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Tennis ball spinning-which direction will lead to?

  1. Sep 13, 2006 #1
    when tennis ball spins sideways like a hurricane. I have seen that if you spin it a little, it turns one way, when you spin it more, it turns the other way. So here are my questions.
    1. Will there come a point as you are inc. angular velocity that it will not change direction anymore?
    2. Will there be a point when it would go straight?(that almost happened)

    When you spin the table tennis ball upside down(works w/ tennis ball too but clearer to see when you play table tennis) The more you spin it, the more it bounces, but if you keep inc. the spin, it comes to the point when the more you spin, the lower it gets. Well, I was wondering will there come a point when it would bounce higher again?

    Thx. for the replies!
     
  2. jcsd
  3. Sep 15, 2006 #2
    Nobody knows? Come on man, if you can't answer all, just answer one.
     
  4. Sep 15, 2006 #3

    rcgldr

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    Assuming that with enough spin the amount of "lift" is reduced for a moving tennis ball, I doubt that this happens in normal play. However if the ball is moving fast enough, the resulting turblent airflow around the ball will prevent it from curving as much; which is the case in baseball, and probably tennis.

    Regarding table tennis, I don't understand your point about how the ball bounces. I assume you mean off the rubber of a table tennis paddle? Again I think the speed of impact is more of an issue. The effect of spin would depend on the elasticity, softness, and thickness of the table tennis rubber sheet used.
     
  5. Sep 15, 2006 #4
    I don't understand your questions at all. As far as I know, if you spin tennis ball in right direction, it's path will be curved to the left. The same with soccer ball, if you kick it with "inner felsh" (supposing you kick it with your right foot), it will turn left. The more you spin it, the more it will turn, but always in the same side.
    I've seen quite opposit happening with balloon, which I can't explain.
    With table tennis ball, did you mean the top spin?
     
  6. Sep 15, 2006 #5

    DaveC426913

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    Re: the tennis ball, I think he means "off the bounce". i.e. some spin makes it bounce left, more spin makes it bounce right.

    Re: the table tennis, I think he's also talking about "off the bounce" but here he's refering to back spin.

    So:
    Spin a ball horizontally slowly, it bounces left.
    Spin a ball horizontally quickly, it bounces right.

    No spin on a ball, it bounces high.
    Spin a ball vertically, it bounces lower.
    Spin a ball vertically quickly, it bounces ... higher?

    I think some of those premises are wrong though. I'm merely trying to illuminate.
     
    Last edited: Sep 15, 2006
  7. Sep 15, 2006 #6

    Clausius2

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    Actually in tennis and baseball the Magnus effect is not that explained by means of the Bernoulli equation. The flow around those balls is usually turbulent (Re about 100,000), generating a NEGATIVE Magnus effect, just in the opposite direction.
     
  8. Sep 16, 2006 #7

    rcgldr

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    In tennis, it's a combination of the path of the ball at impact, and the spin on the ball. Gyroscopic reaction from the court applying a torque to the ball would also be a factor. If you put some right side top spin on a tennis ball, it may be enough to affect the bounce more than the curvature of the path of the ball. Put enough right side top spin on the ball and it curves left, continuing to go left (but a bit less) after impact.

    Backspin reduces the forwards motion of a table tennis ball, but the only change in height is the lift you get from the back spin on the ball as it travels forwards. Normally, a backspin shot is done low, and by the time the ball bounces, there's not a lot of forwards speed, so there's little lift and no significant change in height, just a slight slowing of the forwards motion (not a lot of friction between table and ball), changing the angle of the bounce. A top spin ball can be fast or slow (bubble loop), and the ball increases it's forwards speed after the bounce. The trajectory of the ball just before it bounces can affect the height. A top spin shot made close to the table has a tendency to bounce low and stay low because of the higher speed and more horizontal trajectory. A top spin shot from further away can result in the ball curving downwards hard enough to change the path at the point it bounces, so that it bounces up higher than expected.

    Here's a short clip of the final points of a table tennis match, you can see a significant curve in the top side spin shot, and no unexpected reaction from back-spin bounces.

    tt2.wmv
     
    Last edited: Sep 16, 2006
  9. Sep 16, 2006 #8

    DaveC426913

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    I wonder if the height he thinks he's gaining from a backspin shot has more to do with a misperception.

    A backspun ball, with less forward motion, will bounce more times, simply because it's not travelling down the table as far before it either leaves the table or gets returned. This is in contrast to a fast ball, which might only bounce once.

    What I'm suggesting is that the experience of "hey, that bounced three times on the table" is getting mistranslated to "hey that bounced higher".
     
  10. Sep 16, 2006 #9
    Having played a little table tennis in my day, I might add a little of my perspective to the discussion.

    First, I think some of the original "observational" behavior is mildly misinterpreted.

    For example, if you return the ball with a small forward speed, and some backspin, the ball will "float" a little (travel further than expected before dropping to the table). If you hit it with the same forward speed, but a lot of backspin, it will "float" further, and land rather softly - with little bounce. It will also be moving forward with much reduced speed. Very useful technique to drop the ball just over the net when your opponent is standing back from the table. Point is, the more back spin you put on the ball for a given forward speed, the longer it "floats" and the softer it falls until you reach a point where it has little or no forward speed but still has a lot of backspin. Now the ball actually drops more abruptly and may even bounce backwards due to the spin.

    Those who can provide explanations of the aerodynamics involved can give us the details of what's going on, but I know just enough to realize the "floating" of the ball requires forward speed.

    I believe that the dynamics involved are at the core of the OP observations and questions, and similar issues are affecting the balls behavior for top-spin, and side-spin.
     
  11. Sep 16, 2006 #10
    Oh my god, you guys got it all wrong, here let me try again. You guys were right about the first one, I am talking about if you spin a ball little, it goes to the left, if you spin it more, it goes to the right. Remember, I didn't say I do the w/ the racket, I said I do it w/ the ball. I play cricket, in which I spin the ball w/ my hand.

    About the other kind of spin, I am gonna be extremely specefic this time b/c I tried to be really specific last time.

    While playing table tennis, w/ a tacky rubber, slow blade, the ball tends to spin more. Table tennis is the fastest body moving and most ball revolving game in the world.(speed as much as 60 miles per hour and revolution as much as thousands/min.) Now, I think what I am about to tell you will be more BELIEVABLE

    While playing table tennis, when a ball comes straight at me w/ virtually no spin, my hand motion goes from low to high.(not backspin)-topspin. Here is a page on what it is: http://tabletennis.about.com/od/spin/ss/spinworkcreate_2.htm\
    And here is a slide show clip: http://tabletennis.about.com/od/basicstrokes/ss/fhloopvspush_5.htm

    Ok, now since we have our ground clear, lets move on to what is going on. When I topspin a little, the ball bounces more, when I topspin more, it bounces even more, but when I topspin even more, it starts getting low(lower than it would when it would bounce normally, and faster), and when I topspin more, it gets lower(and faster). But fastness is a common theme(scaler)

    If you play table tennis then please understand that normal people can't get the ball lower b/c it is a really advance(state level) technique.

    Note: I am not concerned about the curve the ball takes in the air, and there is absolutely no side spin(negligable maybe if some)

    My question is, if I continue to topspin, would the ball ever bounce higher again?(as it started to bounce lower the more I spin) And if the answer is no then how low can it get? Can it get so low that ball will immediately bounce again after its first bounce? So inorder to pick it, I have to touch the ball right after the moment of impact? B/c that effect is normally accompanied by chop.

    Sorry, I didn't have any clips or explaination of this from other site, but hopefully, this is specific enough.
     
  12. Sep 16, 2006 #11
    I think you can answer your own question.

    You know that topspin pushes the ball downwards; observation tells you this is so even without understanding the aerodynamics.

    When you put massive amounts of topspin on the ball, when it bounces this topspin fights really hard against the upward momentum from the bounce, rapidly curving the ball downwards again.

    I would hazard to say that you have probably hit the ball pretty darn fast in this instance. This can also have an effect on your perception of the ball's travel. I've watched some high-level games, and it is pretty darn hard to keep your eye on the ball all the time because it moves so fast. It is really by anticipation and experience that you manage to keep it in view at all. But that is conjecture.

    The massive topspin rapidly overcoming the ball's upward motion due to bouncing is really the answer, and should tell you that extrapolating this out suggests there will always be some bounce, it will just be reversed so fast that you won't see it.

    Perhaps at some inhuman rate of rotation, something odd might happen (assuming the ball doesn't disintegrate *lol*), but I'll leave that for the "real" physicists to explain to you. I don't have any idea about that.
     
  13. Sep 16, 2006 #12

    rcgldr

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    Well cricket balls have an unusual design. Here's a link about them and magnus effect:

    http://www.geocities.com/k_achutarao/MAGNUS/magnus.html

    Tacky and elastic (bouncy), just tacky doesn't spin the ball as fast as tacky and elastic, for example, Tackiness Chop versus Catalpult or Mark V. Blade speed doesn't matter much on a top spin / loop shot, since the idea is to graze the ball rather than make very solid contact with it.

    and the racket is "closed", angled forwards, (else the ball would leave the racket at a very high angle, way above the table).

    As I mentioned before, it is a combination of the top spin, speed, and the direction (angle) the ball is moving when it contacts the table. Some combinations of spin, forward speed, and the maximum height of the ball above the table cause the ball to curve downwards at a steep angle, and the result is a higher bounce. The lowest bounce height occurs when the ball is struck from close range, say from above the table as opposed to behind it, so that there is little distance or time for the ball to curve. It's called a loop drive shot, the stroke motion and the racket angle are almost horizontal, and the ball path is very near horizontal, just missing the net, hitting the table at a shallow angle, and the top spin causing the ball to bounce off shallower still and curve downwards.

    Regarding the limits, I had experience with a Stiga robot (back in 1972). This machine is similar to a baseball pitching machine, with two spinning wheels running independently to propel a table tennis ball. The machine can be set to generate a lot of spin and speed. With the machine and in real life, I've never seen a high speed ball that would bounce twice on the table. Stiga doesn't appear to make such a robot anymore, but Butterfly makes a similar one (two spinning wheels):

    butterfly robot htm

    I have seen many cases, like a looper versus a chopper, hitting the ball so that the chopper can't back up very fall as the ball curves downwards towards the floor forcing the chopper to return the ball from down low, or from closer in to the table (neither of which choppers like to do). The guy in the video clip from above, Jan Ove Waldner, ranked number one back in the 1990's and in the top ten for over twenty years (still in top ten as of last year), was probably the best player against choppers, (also considered the best all around player ever). Do a web search and you shot find a lot of hits. Here's that clip again:

    tt2.wmv
     
    Last edited: Sep 16, 2006
  14. Sep 16, 2006 #13
    Actually the best spin occurs when the speed is least and the racket has no forward motion but just from down to up. As it barely touches the ball. The faster you swing it from up to down, the greater it spins. As in the motion, your hand speed doesn't increase the speed of hte ball(may be a little), it rather increases the spin. What rating are you guys in table tennis btw?
     
  15. Sep 17, 2006 #14

    rcgldr

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    In my experience, the most spin occurs when the ball has a lot of backspin before it is struck. In order to strike a heavy backspin ball by grazing it on the upper back (almost on the top) side of the ball, a loop drive shot, the ball needs to be struck soon after the bounce, while the ball is still moving upwards. As I mentioned before, the stroke motion and blade angle are almost horizontal. This generates a lot of top spin on the ball, and requires a very large amount of blade speed at the moment of contact. The timing requires precise anticipation, since to generate a lot of blade speed requires a lot of back swing followed by a lot of forward swing on the stroke in order to achieve a high rate of blade speed at the moment of contact, and this has to be timed so the contact occurs while the ball is still moving upwards, and into the path of a closed blade which sweeps a narrow area in the path of the stroke.

    Personally, I haven't played much in years. I only played in two tournaments when back when I first started, winning a couple of lower rated events on my second tournament. Based on club competition, the best I got was about 1850 USA rating, and this would be a couple hundred points lower on a world rating system. One of the top 4 USA players lived nearby though (this was back in the late 1970's), and I saw his matches, and occasionally practiced with him. We also had a coach from China visit for about 2 months in the early 1980's and this helped me improve to my best level (the 1850 level as mentioned). Due to a shoulder injury, I quit playing for a while, and after it healed, the place I played at shutdown, and I was unwilling to commute 45 minutes to an hour each way to go to the other active places for table tennis.
     
  16. Sep 17, 2006 #15

    rcgldr

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    I editted another video, including normal and slow speed views. The first clip shows the more vertical stroke motion type loop, where there isn't a lot of forward speed, the remaining clips show the loop drive where the stroke motion is more horizontal and uses a lot more blade speed, and both the speed and the spin are much faster with the loop drive. The advantage of this shot is that since the motion is near horizontal, it can be done above the table, while the near vertical stroke can only be done from behind the table. In order to be able to use more blade speed on the more vertical motion, you have to wait for the ball to be moving downwards significantly so the ball won't end up going too high. The near horizontal motion doesn't have any limitations, other than the skill level of the player, and as noted, the ball has to be struck while it's still moving upwards from the bounce off the table. If a player waits until the ball reaches it's peak, there won't be enough contact for the near horizontal stroke and blade angle to work, the blade will have to be opened up, which will increase the speed, but it's a lower percentage shot.

    Note, there's no sound on this video:

    tt3.wmv
     
    Last edited: Sep 17, 2006
  17. Sep 17, 2006 #16
    I use both shots and tons more. Depending no the ball, every ball has its own kind of shot to hit. I am not like one of thsoe players who master in one kind of shot. I got varities, tons of it. Btw, I was wondering, scientifically, when I loop the ball just vertically, and when I loop it horizontally. Which one would spin more and why?

    I know that we aren't agreeing on spin more but if you could explain to me scientifically, what happens that makes the ball spin more, it might be a bit more convincing.

    Also, nobody answered my first question. If I spin a tennis ball sideways by my fingers, like a hurricane, when I spin it a little, it goes to the left, when I do it more, it goes to the right.(I never was talking about cricket ball, I am talking about playing cricket w/ a tennis ball) I was just wondering if there is an exact spin I can do in which ball will rotate but instead of going either left or right, it will go straight! B/c that will be very deceiving.
     
  18. Sep 17, 2006 #17

    rcgldr

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    When you change or increase the spin on the ball, it causes the ball to also move in the direction of the stroke, because of the resistance to the change in angular momentum, and the fact that the contact is made in the direction of the stroke.

    Assuming that a player is trying impart a path that keeps the ball reasonably close to the net as it crosses over the net (as opposed to very high lob), a vertical stroke motion's speed is limited by the amount of spin on the ball before contact (backspin would allow for more blade speed) and it's downward component of velocity before contact (more downwards speed would allow for more blade speed). Bottom line a vertical motion is limited because too much blade speed will result in the ball moving upwards too much (too high an angle). To further increase the spin without the ball moving upwards as much, you need to adjust the angle to be more forwards. This will increase both spin and speed though. The near vertical motion will produce a high spin, low speed shot if that is the goal.

    Most of the time I see players using near vertical motion is when the player is back, or the ball is dropping downward before contact, or there's a lot of backspin on the ball. When the player is spinning while near the table, the motion is more forwards, probably ranging between 45 degrees to near 80 degrees from vertical.
     
  19. Sep 17, 2006 #18
    hmm strange, for me, the ball goes the slowest, and spinniest when the motion goes from down to up b/c that way, I don't focus on speed as much as spin. When I loop more forward, speed increases more and spin decreases. Btw, what kind of shot are you talking about, where you barely touch the ball(like brushing it) or where you spin the ball by applying more force on it?
     
  20. Sep 17, 2006 #19

    rcgldr

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    Brushing the ball, although some increase in force won't decrease the spin. I learned this from the Chinese team coach when he visited Southern California for a 2 month clinic, that you can graze the ball too thin, and that a slightly more open racket will produce more spin due to better contact.

    Still, the blade angle versus the stroke angle determines how much you "brush the ball", and this can be done with any stroke angle. I've done my share of near horizontal loop drive shots on short balls, sometimes having to run around the side of the table to position for the shot on a really short ball, as the table blocks the path for anything else. This happens more in doubles or against a chopper that doesn't place the ball deep enough.

    On my forward motion loops, both spin and speed increase, but speed increases more, so the ratio of spin to speed is less. Take a good look at those videos again. On those loop drive / loop kill shots the blade angle is near horizontal at contact, I'd call that brushing the ball. In spite of the speed, there's a significant downwards curve in the balls path after contact.

    If you look at that first sequence in the tt3.wmv, the ball has backspin, it's dropping and struck from well below the table, so a near vertical motion is used. Here is a link to videos of old events: http://tt.mainstreet.net/HungaryChina1981, the first video shows the off the floor near vertical (and some sideways) motion, but most of them are more like loop drive shots with more forwards motion. This was first time in recent history that the Chinese team got beat. It was almost 10 years later before Sweeden accomplished the same thing (Pearson and Waldner being the top two players on the team, Waldner going on to dominate Table Tennis for a few years, although a few other players, including Pearson were rated # 1 on and off during Waldner's "reign".

    Part of this depends on the type of table tennis rubber you're using. Mark V for example, is very elastic, both in bounce and in reversal of spin, and with Mark V and similar rubber sheets, some forwards motion is going to give you more spin than a vertical motion, especially if you're countering a loop with another loop (when one or both players are back from table). Currently, I have Stiga Innova Premium, a more controllable and lighter rubber than Mark V, but with similar speed and spin response, however, my company closed it's gym quite a while ago, so there's no table anymore, and the closest club is inconvenient, too far and only weekends (family time).

    Personally and from watching modern top level players, the near vertical loop motion is normally done in special circumstances as I mentioned before (backspin, dropping ball, below table level).

    For those not familiar with the amount of friction and elasticity of table tennis rubber, I made a short video. In the second part, I reverse the spin back and forth, striking the ball with a fairly slow motion, but there's enough change in momentum from spin reversal that the ball moves near vertical, inspite of a steep racket angle (about 45 degrees or more from horizontal). Imagine the effect with a lot of blade speed instead of just the small motion I use in the video.

    ttstick.wmv
     
    Last edited: Sep 17, 2006
  21. Sep 18, 2006 #20
    If you take the blade upside down( ball totally facing the floor) w/ a tacky rubber like hurricane, the ball will still stick, for long. Btw, where did you get that first clip from? tt3.wmv?

    While looping, do you think concave spins more? Convex? or straight? I know this depends on weather you are using tacky rubber or not but lets discuss both.

    I would pick concave on both of them. What do you think?
     
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