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  1. #18
    Regular Member craigandy's Avatar
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  2. #19
    Regular Member Tadashi's Avatar
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    VERY LONG POST - you asked for it though.

    Quote Originally Posted by craigandy View Post
    I am not sure if I understand what ...
    PITCH

    There is a nice PSU webpage asking this: "How is it possible that two bats with the same actual weight feel like they are 8 ounces different when they are swung?"

    That's what people usually feel about the weight .. but it's not about the weight.

    ACT1

    But let's talk about head-heaviness and weight first.

    I find throwing tennis balls simpler to throw than a shuttlecock or a ping pong. Note that tennis balls are heavier!

    When it comes to head heaviness, look at baseball bats. Baseball bats have a certain design, a shape, they are fatter at the end, and thinner at the handle. By design, power goes better into the ball if the bat's end is such and such times bigger than the ball itself. See, a bigger billiard ball kicks a smaller billiard ball much better - same thing with "head heavier" baseball bats.

    You can mimick this for any badminton racket by making heads "heavier". That's what the producers do ... they put in a little bit of metal inside the frame at the 12 o'clock tip so it becomes "head heavy." Typically, they have the label "professional" and the AT800 successors would be it, on their balance-flex matrix look at the top and top-right corners, there you have all the nice rackets for hitting.

    (Of course, not everybody can handle a head heavier racket and baseball bat, because most have weak underarms - it's not the racket, it's the weak underarms that cause problems - see that's why there are tennis elbows, and producers say "for professional/tournament" for a reason.

    The true thing about these high priced rackets is: the harder the string tension, the more muscle training you need to handle them, and the harder you can pull, the better engineering must go into your racket frame to withstand forces - which justifies higher prices.

    It also was found that (better) skill correlates with (higher) ball speed/striking speeds, regardless of what racket, so that better players actually need better engineering.)

    Since this is about weights and not about strings tension (although measured by kilograms/pounds, too), not about skill, I skip the problem with strings and I skip the material stiffness and skill, too. That you, please, ignore.

    ACT2

    Now the original, the first, the prime question of THIS thread was: if you lower the grams or have more grams, what's the effect on ball speed. Right?

    The science experiments (DOI 10.1080/02640410500127876 or [2] in the references) suggest the following: from a certain threshold somewhere between 100 and 200 gram onwards up to relevant 1000 grams for any racket (tennis is about 300+ g), the striking speeds do not differ much on average. Okay, again. Take a light racket of weight 100g, a heavier one of 200g and a heavy 300g racket --- do you see increases in striking speed? Not really. 1000g? Not really. Do you see drops in striking speed? Not really. On average, striking speed doesn't change as you change heaviness within these bounds.

    Why it does not change? Because the experiments kept the moment of inertia constant. The 100g racket has had a similar moment of inertia as the heavier rackets. Hence, the striking speed remained relatively the same. There also was not much about striking skill, because they only hit the racket down like knife-cutting and chopping vegetables, or beheading a chicken. Just down. Not much about skill either. So "all else equal," as visor said.

    But why is a tennis ball better to throw than a ping pong? Because among other things, there seems to be this threshold. Below the threshold, you strike/throw faster as the thing gets heavier (from ping pong to tennis ball), but above the threshold, that's no longer true (100g rackets, 200g, 300g). So I say 100, 120, 150g, there you have the threshold. A tennis ball in hands changes your hand's weight much more than a ping pong and you stay below the threshold!

    The thing is that you don't play 150g badminton rackets, you play 85g. So you could buy a 90g or a good old iron-wood frame - I have one, it weights 110g, but it actually is as easy to strike as the modern rackets, and it would increase strike speed compared to a kids' racket of 65g. How do I know? Well, there are other experiments that show it clearly ... weighted badminton rackets correlate with higher striking speeds (measurable and statistically significant but in practice by a ridiculous small margin).


    However, 100g is heavier than 85g and holding heavier things needs (little) more energy, so you can get tired by that little extra weight, I assume. Unless you train your underarm ... which ... as I said ... well, not many people do that, and that's why people like lighter rackets for they would like to swing faster, but they actually like to play ... longer.


    Still, some rackets of the same weight can feel very different. You see, most rackets you buy have a narrow margin of 80 to 90 grams in weight. By numbers, that's just 10 grams maximum difference ... not much, really not much, it's so narrow you could say that there is no real difference.

    But people feel differences when swung.


    ACT3


    Now about swing weight ... pretty simple: lower swing weight, faster swinging; higher swing weight, slower swinging. All experiments show this. Check the DOI above. You can also check the graphs on the net - it's all round the web, if you look for it, you find it, it's in the public domain. Nothing mysterious, completely old information, almost trivial, no drama there, and nothing to dispute.

    This PSU graph, from a Penn State University page [1], USA, http://www.acs.psu.edu/drussell/bats...s/moi-data.jpg shows exactly what I just said in lavishly long paragraphs. It shows the same results as in DOI 10.1080/02640410500127876, which comes from University of Sydney, and University of Technology, Sydney, Australia. Both confirming what I said here, or put it differently, I only report what was confirmed by them independently around the world. So please, no drama. All information is strikingly trivial, old and conventional.

    What you see -- Left graph, on the up down axis: SPEED. Right graph, on the up-down axis: SPEED. So speed is on the y-axis. Left graph, on the left-right axis: WEIGHT (mass). Right graph, on the left-right axis: SWING WEIGHT (moment of inertia).

    On the left graph, there is no change in speeds, but the data points refer to different weights. Right graph: the speed goes down, as the swing weight goes up. Lower swing weight, faster swinging; higher swing weight, slower swinging. Different masses, same speeds.

    Now I only cite what Mr. Russel from PSU writes: "Before you run out to purchase a new bat with lowest moment-of-inertia you can find in order to increase your bat-swing speed in hopes of hitting balls faster, there is a catch. It is true that lower MOI translates to higher bat-swing speed, and that higher bat-swing speed results in higher batted-ball speed. However, a gain in batted-ball speed only results if you are swinging the same bat faster. Swinging a lower MOI bat faster does not resulting in a faster batted-ball speed. "

    EPILOGUE

    If I remember correctly, someone said that Yonex promotes a new racket that can run 20% faster through air? Well, it's the shuttlecock that needs 20% more speed, not the racket swing alone.

    If you remember ... big billiard ball kicks small billiard ball much better. Then you recognise that swinging is not hitting and the physics of hitting is not swinging alone. So, first you need to swing much better and faster, that means mucles, nerves, innervation and training - not just lowering the swing weight! And then this superbly faster power must translate into ball speed at impact, too, hence the racket design and the string and the stiffness and the material and the impact point on the strings ... lots of stuff going on in hitting.

    So, you cannot simply find a one-to-one causation from A to B. That's just not there. If a salesman tells you so, don't buy.

    REFERENCES

    1. Russell, D. A. Swing Weight: Why moment-of-inertia matters more than weight. (2008). at <http://www.acs.psu.edu/drussell/bats/bat-moi.html>
    2. Cross; Bower: Effects of swing-weight on swing speed and racket power, Journal of Sports Sciences, January 2006; 24(1): 2330
    Last edited by Tadashi; 06-24-2013 at 04:31 PM. Reason: Minor changes here and there..

  3. #20
    Regular Member Tadashi's Avatar
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    Quote Originally Posted by amleto View Post
    I agree it's not very clear. I think Tadashi changes his meaning when he's talking about speed - sometimes he's talking about racket speed, sometimes it looks like shuttle speed (it's not obvious).


    The punchline is obviously wrong in part as well since he says adding tape gives a faster smash AND faster swing. However, earlier on he says lower swing weight gives faster swing (correct).
    Absolutely correct, the earlier thing wasn't very .. say accurate. There are so many different speeds out there I always get confused. There is the racket head speed, which is swinging. There is are multiple other angular speeds at various points of the racket, which is still swinging. Then there are different speeds of the shuttlecock, like the speed at impact, before the impact and the terminal speed after the flight downwards ... there are different speeds ... I apologize.

    However, I honestly remember that is quite correct that adding tape makes a great smash ... for reasons states in the second post, I have to check what happens to swing speed by adding tape/extra weight.
    Last edited by Tadashi; 06-24-2013 at 04:42 PM.

  4. #21
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    Quote Originally Posted by Tadashi View Post
    However, I honestly remember that is quite correct that adding tape makes a great smash ... for reasons states in the second post, I have to check what happens to swing speed by adding tape/extra weight.
    swing speed must go down if the only that that changed was increased MoI.

  5. #22
    Regular Member Tadashi's Avatar
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    Quote Originally Posted by Tadashi View Post
    I have to check what happens to swing speed by adding tape/extra weight.
    Yep, swing weight goes up significantly with extra weight, counterintuitively against the "higher-swing-weight makes slower swinging" the ball speed also goes up but only if hit on the right spot on the strings, otherwise ... lots of other stuff going on but I quote the guy studying this ....

    "it is clear that mass added at the tip of the racket is effective in increasing racket power and that the point of maximum power is shifted towards the tip of the racket" [1:14]

    He defined racket power as ball speed right after impact and maximum power is the situation when you do loose a minimum of physical energy due to vibration upon impact - (coefficient of restitution COR, if this is something meaningful to you ... in simple terms - the trampolin)

    [1] Cross: Customising a tennis racket by adding weights, Sports Engineering (2001) 4, 114

  6. #23
    Regular Member craigandy's Avatar
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    One thing that's important is OP however stated
    1st racket weight 78gr with same spec such as stiff and head heavy
    2nd racket weight 86gr with same spec stiff and head heavy too

    An 86g racket with the same bp in mm as a 76g racket(say bp300mm). The 86g racket will have higher swing weight. So if BP and shaft stiffness the same there is still a valid discussion.

  7. #24
    Regular Member Tadashi's Avatar
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    Quote Originally Posted by amleto View Post
    swing speed must go down if the only that that changed was increased MoI.
    it's really funny, this extra-weight study came before the swing-weight study, but he mentions that ball speed surely depends on the swing speed, which we now know depends on lower swing weight ... and the next thing is that a change in the vibration upon impact is less important than the swing speed ... however he comes up with great wizzardry --- or I just be too lazy to read all again and double check elsewhere, I admit that --- ball speed up with weights if hit on the right COR spot.

  8. #25
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    Quote Originally Posted by craigandy View Post
    Interesting read. Unfortunately the study explicitly elimintated internal rotation and pronation from the swing used to generate the data . So yeh, they used a tennis swing and not a badminton swing.

  9. #26
    Regular Member Tadashi's Avatar
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    Quote Originally Posted by craigandy View Post
    The 86g racket will have higher swing weight. So if BP and shaft stiffness the same there is still a valid discussion. [/COLOR]
    As such the swing speed for the 86g racket may suffer, compared to the 78g racket, but:

    From Russel, see earlier post of mine - "this increase in batted-ball speed results from an increase in bat-swing speed for the same bat. Swinging a given bat faster will result in a faster batted-ball speed. However, swinging a lower MOI bat with a faster swing speed will not increase the batted-ball speed."

    I think it's pretty clear ... the answer is no.

    @happy

    Oh please, we just figured out what it is about the different weights Don't come up with angular speeds of pronation etc.( ... but wait I also remember that the torso rotation and later the pronation (underarm) and the rotation of the wrist that are the fastest and greatest contributors to smash speed, if this is what you look for)

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