Centrifugal force on spinning ball?

Discussion in 'Tennis Tips/Instruction' started by pondus, Sep 8, 2009.

  1. pondus

    pondus Rookie

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    If a ball is spinning at 2000 rpm, is there any measurable effect due to centrifugal force? Has any study tried to measure this, or is there a simple physics formula that can be used to cast light on this?
     
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  2. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    Perhaps if you were an ant riding on the outside or inside of a tennis ball the centrifugal or centripetal force might be significant. Not sure that these forces are large enough with a tennis ball spinning at 2000 rpm to have any noticeable effect on the shape or playing characteristics of the ball.

    However, the Magnus effect due to the ball spin is very significant. Any ball with topspin, underspin or (vertical axis) side spin will experience a change in trajectory due to the Mangus effect. On the other hand, spiral spin will have no net Magnus effect.

    .
     
    Last edited: Sep 9, 2009
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  3. jrod

    jrod Hall of Fame

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    SA- I'm sure you've seen balls hit that are no longer appear to be perfectly spherical (egg or oval shaped). My observation is that when someone hits a ball like this it has a tremendous amount of spin. While I can understand the initial contact distorting the ball's shape, it's not clear to me why the ball doesn't return to it's spherical shape right away.

    What do you think causes these types of balls to remain (or appear to) distorted in shape for a good part of the flight? I'm of the opinion the spin contributes to the ball retaining it's distorted shape longer...
     
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  4. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    No, can't say that I've really noticed balls being non-spherical while in flight. I suppose that this may happen, but can't say that I've really been aware of it. High speed photography shows that the ball's shape becomes extremely distorted on contact (with ground or racquet). Do you have any photos that show shape distortion while in flight -- some time after contact?
     
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  5. Nellie

    Nellie Hall of Fame

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    I would argue that a "heavy ball" is due to the gyroscope effect of the spinning ball - which is way harder to calculate than centripetal force.
     
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  6. jrod

    jrod Hall of Fame

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    I don't have any photos but I definitely have seen it. I hit with a lefty who hits with massive topspin and he occassionally will send one over the net. I think it has also happened with mishits where the ball makes contact with part of the frame. In all cases the ball appears to be spinning at a very high RPM's and takes on a subtle oval/egg shape. I can't recall how the shape relates to the axis of rotation, but next time I see it I will try and take note.

    I wonder if there are any pics or slo-mo video of this phenomenon out there???
     
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  7. jrod

    jrod Hall of Fame

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    SA- I googled around a little and found nothing in the way of pics. I did stumble across a fairly interesting study which included fairly sophisticated simulation models of a ball in flight, but nowhere do they suggest the shape is distorted.

    Here is the site: http://wings.avkids.com/Tennis/CFD/cfd-02.html

    I'm wondering if you got a ball to spin fast enough whether the differential pressures might cause some slight compression in one axis? Seems pretty improbable I know, but there has to be some explanation of what I am seeing (aside from a flashback that is...).
     
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  8. LeeD

    LeeD Bionic Poster

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    C'mon guys, even I, as a lowly bad 4.0 ancient player, can hit a ball that goes oval a little, hiss's a little with audible noise, and can distract the lesser level players just by it's sound and shape.
    Those top players easily hit the ball into those shapes all the time, and it's a normal shot for them.
    Don't you guys ever play against decent players.....ever?
    My second serves usually return to normal shape by the time it goes to the opponent's strike zone. However, some of my opponent's can keep the oval effect and noise all the way to the backboard. But they are like 6'6", 200lbs., and were ranked top 200 in the world.
    Gee willikers, who ARE on these forums, anyways?
     
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  9. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    A lot of players can't even tell what kind of spin a ball has let alone the shape of the ball. Never really focused on the shape of the ball -- always been focused on the spin & the trajectory. I don't doubt that the ball is not perfectly round at high spin rates but I would have probably noticed if it was significantly non-spherical.
     
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  10. benasp

    benasp Semi-Pro

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    The ball need to be very old or pressureless to get oval. A new ball will never do that. At least i only seen that with old ball on miss-hit
     
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  11. LeeD

    LeeD Bionic Poster

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    I notice the ovalness and hissing sound because I used to regularly play with guys who served over 130, and swung FASTER for their second serves. I NEVER noticed my serves doing that until opponent's started telling me.
    When a former #4 in the world tells me my serve goes oval and hiss's, I tend to listen and retain. His didn't! He'd hit his first serve faster than mine, but took swing speed off for his second serves (DickStockton).
    But I played KevinCurran, then 17, the following year, and ALL his serves made audible noises AND were hit with enough spin to go oval.
     
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  12. jrod

    jrod Hall of Fame

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    ^^^ True...sometimes there is a hissing-like sound with these types of balls. It's actually more noticeable than one might think.
     
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  13. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    Hissing sounds, huh? I'll have to listen for that (& look for the oval as well) the next time I playing with someone who employs heavy spins at high speeds. I suspect that the sound has more to do with air turbulence than with centrifugal or centripetal force tho'.

    Note that the 2000 rpm that the OP was talking about is only moderate spin. A ball with 1000 rpm (or less) would be considered "flat" for most types of shots. Doubt that there would be very much ball distortions at spin rates of 1000 or 2000 rpm. Heavy spins would be on the order of 3500 to 5000+ rpm.
     
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  14. HunterST

    HunterST Hall of Fame

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    It's centripetal force.
     
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  15. ubermeyer

    ubermeyer Hall of Fame

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    I heard that when Agassi hits the ball it always looks like an egg... and Nadal hits more spin than he does
     
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  16. jrod

    jrod Hall of Fame

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    Right, these numbers were provide in the url I cited above. In all honesty I have no idea what RPM's are associated when the ball distortion occurs but I can tell you that the spin is extreme, even uncanny. It invokes a degree of dread in the returner since there is substantial ambiguity as to where the contact point will be after the ball bounces.
     
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