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  1. latej is offline
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    #21
    Quote Originally Posted by Atas Newton
    well if it's the same diameter and mass, but thinner, then it's gonna be more reluctant to spin, no?
    Yes, undoubtedly. An analogy would be that a heavier object is more reluctant to movement. So if you convert the same energy to the rotation of those 2 TT balls (same shape and weight), so that now they have the exact same rotational energy, then the one with thinner shell will rotate slower. Which also means that if they rotate equally fast, then the one with thinner shell will have more rotational energy, and may appear to us as having a heavier spin.

    But with the very same stroke you will not impart the very same energy to those 2 balls, imo. An analogy, if you take TT ball and golf ball and throw them with the exact same movement, say as fast as you can, the golf ball will have significantly more energy. They will have very very similar speeds though, at least initially. This analogy is a bit imprecise, because it is not really a collision between those balls and the hand, but I am using it because it is so easy to visualize. Similarly, with the very same stroke, the 2 TT balls will not receive the exact same rotational energy, because what happens between the ball and bat has elements of both a bounce and of a throw. After all, we tend to speak about the dwell time and the throw angle. So, imo, the 2 TT balls will have different rotational energy (the one with thinner shell will have more rotational energy), and similar spin (speed of rotation). Perhaps not as similar as the thrown balls (TT ball and golf ball), I can't quantify.

    I thought that the ball with thicker shell will get a bit more (faster) spin initially. But I simply don't know. What Zwill said is very interesting. It may be, that due to, let's call it, details of how the imparting of spin actually exactly happens between the ball and bat, that the ball with thinner shell, may even get more spin (not only more rotational energy). I don't know. Hopefully Someone can explain eventually.

    Anyways, Igor says the one with thinner shell rotates faster. We don't know how he measured. Maybe they rotate almost equally fast, but the one with thinner shell he perceived as a heavier spin, as I mentioned above...

    I hope it's OK I replied to this question. It's possible the differences are negligible. It is absolutely clear it has not much practical TT meaning. But where do you draw the line? Finally, I will not reply to incoming accusations in this thread.

  2. Zwill is offline
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    #22
    I think what you are saying is sound. It shouldn't make much difference how much rotational energy a ball can take during the stroke based on the wall thickness of the ball, but it makes a bit more difference that thinner wall balls will keep their rotational energy for longer.

    Actually I really am curious about the weight of the balls, I would be shocked if the difference was only 0.01-0.02g between brands. Even in my hand I can feel some weight difference between balls and for sure my hand cannot tell a difference between 0.01g-0.02g.
    I don't know what other reason would a DHS ball fly faster and lose its speed slower than a seamless ball.

    But a different weight ball would have a different effect on both the racket and the rubber. Since I tend to play with harder rubbers like Dignics or Hurricane (or I would even consider Tenergy and Rozena on the harder end of the scale) a heavier and lighter ball makes a noticeable difference on these rubbers, how much the sponge is compressed and how much the rubber is stretched. (or how easily the ball "hits down" on the wood)

    There are videos online where pros discuss that even the size of the venue makes a difference on their game, the temperature of the area as well. So why wouldn't the weight of the ball make a difference? To me it sounds very obvious.

    I feel the DHS balls are heavier than seamless balls, so DHS balls work better with harder rubbers. If someone is playing with seamless balls maybe it's not the worst idea to consider to chose softer rubbers to get the similar gameplay feeling, similar spring and stretch effect.

  3. latej is offline
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    #23
    I have a scale with 0,1g precision from my youth :-). Not very precise but at least something (measured 2 of each mark):

    DHS D40+ 2,7g
    Tibhar 40+SL 2.8g
    Hanno 40+ 2.8g
    Sanwei 1star 2.7g

    Some Joola and Xushaofa I can measure later.

    The senses are misleading. When I take DHS and Tibhar in the hand, I'd say DHS is harder and heavier, and Tibhar is lighter, but it is the opposite - the weight. Can't measure the hardness, may be opposite too... I like both more than Joola and Xushaofa in play (those feel quite differently too).

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    #24
    You don't measure the weight of each ball one at a time. Weigh 10 balls at a time then average.

    The senses are misleading
    YES! I have been saying that for over 10 years. That is why I can record motion at rates up 4 kHz easily. I have had too many customers telling me what they think they see. Only when they see the high speed recordings that they finally understand they aren't calibrated machines.
    Everyone has their "feelings" and opinions but what are the facts to back them up

    I don't know what other reason would a DHS ball fly faster and lose its speed slower than a seamless ball.
    It would take a larger impulse ( force x time ) to accelerate the heavier ball to the same speed as a lighter ball so you aren't doing an apples to apples comparison. However, the percentage difference is small. A heavier ball wouldn't slow down as fast. There is a differential equation for computing how the speed of the ball ( sphere ) will slow down. TT balls will slow down approximately by 50% after the ball travels 5 meters which is about the distance between two players.

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    #25
    If we assume that the seam is thicker than the shell, in which situation the ball will spin faster?
    1. When the seam plane is in the flight direction
    2. When the seam plane is perpendicular to the flight direction


  6. latej is offline
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    #26
    Quote Originally Posted by langel
    If we assume that the seam is thicker than the shell, in which situation the ball will spin faster?
    1. When the seam plane is in the flight direction
    2. When the seam plane is perpendicular to the flight direction
    I think 2. If we consider the seam to be extra matter, then in case 1 all this extra matter is at radius r from the center, and in case 2 it is distributed at varying radii (0, r). So imo, the ball will be a bit more reluctant to spin in case 1.

    Edit: Langel, I guess this is not what you asked. So whether or not the same stroke would actually impart more rotation in those 2 case is for me unknown, for the same reasons as before with the thicker and thinner shell...
    Last edited by latej; 12-09-2021 at 12:55 PM.

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    #27
    Quote Originally Posted by latej
    I think 2. If we consider the seam to be extra matter, then in case 1 all this extra matter is at radius r from the center, and in case 2 it is distributed at varying radii (0, r). So imo, the ball will be a bit more reluctant to spin in case 1.

    Edit: Langel, I guess this is not what you asked. So whether or not the same stroke would actually impart more rotation in those 2 case is for me unknown, for the same reasons as before with the thicker and thinner shell...

    Thank you, I've noticed your reply and the edit.
    I have to admit that their is a hidden question, but the main one is absolutely on the table too. About the hidden one - later.
    For now I'm still waiting for some more answers.


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    #28
    You guys are arguing about minute differences that you really can't feel the difference since they are so small

    Forget which orientation will spin faster because that depends on a lot of different factors. Lets just concentrate on which orientation of spin will have the greater inertia. This is simple. The inertia will be higher if the axis of rotation is normal ( perpendicular in two dimensions ) plane of the seam.

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    #29
    Quote Originally Posted by brokenball
    You guys are arguing about minute differences that you really can't feel the difference since they are so small

    Forget which orientation will spin faster because that depends on a lot of different factors. Lets just concentrate on which orientation of spin will have the greater inertia. This is simple. The inertia will be higher if the axis of rotation is normal ( perpendicular in two dimensions ) plane of the seam.

    Of course, and here comes the hidden question - what is the chance to hit the ball at "normal plane"?

    What about the "zig-zaging" ball?


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    #30
    [quote="langel;358433" - what is the chance to hit the ball at "normal plane"?[/quote]
    This isn't clear to me. The earth's axis of rotation is normal to the planes described by the equator. The axis or rotation is not a plane.

    What about the "zig-zaging" ball?[/p]
    What does a zig-zagging ball have to do with rotational inertia?
    To the outside world the ball looks like sphere and mass unless you think a raised seam influences the air flow over the ball. TT balls have seams but they are like the seams on base balls if that is what you are getting at.

  11. latej is offline
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    #31
    Quote Originally Posted by langel
    What about the "zig-zaging" ball?
    You can visualize how much volume of the ball the seam-plane takes when the ball rotates, at various orientations. It can take the whole ball (case 2), or very small volume (case 1), or something in between (zig-zag). Approx. so varies also the inertia (case 1 highest, case 2 lowest).

    Btw. they abandon seamed balls because with them ML can control the Dzhanibekov effect at will, and that poses serious problem to non-chinese players. Rumor is, he is getting to it with seamless balls too - if you ask why he couldn't participate at the 2 recent finals events...

    Edit: Adding here, don't want to spoil AN's post:
    Quote Originally Posted by langel
    Of course, and here comes the hidden question - what is the chance to hit the ball at "normal plane"?
    He meant normal to plane, but forgot to write "to".

    The chance, if you give tolerance 1 degree, is very small, cca 0,005% (I was wrong before, can be wrong again).
    Last edited by latej; 12-13-2021 at 08:59 AM.

  12. brokenball is offline
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    #32
    Quote Originally Posted by latej
    You can visualize how much volume of the ball the seam-plane takes when the ball rotates, at various orientations. It can take the whole ball (case 2), or very small volume (case 1), or something in between (zig-zag). Approx. so varies also the inertia (case 1 highest, case 2 lowest).
    Did you understand the video? It specifically stated that the moment of inertia must be different between the 3 axes of rotation. This isn't true for a TT Ball. If the seam is the equator then rotating around the north and south pole axis is higher than the other two axes but they are the same.

    Btw. they abandon seamed balls because with them ML can control the Dzhanibekov effect at will, and that poses serious problem to non-chinese players. Rumor is, he is getting to it with seamless balls too - if you ask why he couldn't participate at the 2 recent finals events...
    Neat video but I call BS on Ma Long being able to control it. The video makes is clear that this effect is a property of the rotating device, not the player or the force he applies. Then again, the seamed TT ball is symmetrical around two of the non-polar axes. Also, the effect in the video happens quickly in the video because the wing nut's three axes of rotation have greatly varying inertias.

  13. Atas Newton is offline
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    #33
    It's just a joke :-)

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    the commentator lists Grand Slam winners, calls JOW John Oev Wellner, LGL Louis Goodland (not kidding)

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