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  1. #35
    Regular Member gundamzaku's Avatar
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    Quote Originally Posted by Olivier P. View Post
    Just my 2 cents as a physicist.

    Momentum of inertia
    I think that the quantity that describes whether a racket is head-heavy or head-light is indeed the moment of inertia. However this is not described as a sum of W x D but as a sum of W x D^2 (distance squared). The distance D has to be considered from the pivot point, that is, where the hand holds the racket.

    - The momentum of inertia is proportional to the energy that one needs to give to the racket to swing it (i.e. rotate) at a given (angular) speed.

    - The total weight of the racket determines how hard it is to translate it at a given (linear) speed.


    Balance point
    The balance point is defined as the point, dividing the racket in two, where the sums of W*D to the left and to the right are equal.

    It's clear it is a very different physical quantity from the momentum of inertia, the reason being that one is related to distances from the balance point whereas the other is related to distances squared from the grip.

    This explains why changing the grip weight will affect the balance point while not changing the "head heaviness" feeling of the racket. Another way of seeing that is by adding, let's say, 50g at both ends of the racket. The balance point is not changed but the feeling is now extremely head-heavy (and unplayable...).

    Since different rackets have more or less the same shapes, the balance point is somehow related to the "head-heaviness" feeling, but that's not the actual parameter that matters.

    Hope that helps...
    finally someone who can actually speak with authority. thank you for the explanation!!!

  2. #36
    Administrator kwun's Avatar
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    Quote Originally Posted by Olivier P. View Post
    Just my 2 cents as a physicist.

    Momentum of inertia
    I think that the quantity that describes whether a racket is head-heavy or head-light is indeed the moment of inertia. However this is not described as a sum of W x D but as a sum of W x D^2 (distance squared). The distance D has to be considered from the pivot point, that is, where the hand holds the racket.

    - The momentum of inertia is proportional to the energy that one needs to give to the racket to swing it (i.e. rotate) at a given (angular) speed.

    - The total weight of the racket determines how hard it is to translate it at a given (linear) speed.


    Balance point
    The balance point is defined as the point, dividing the racket in two, where the sums of W*D to the left and to the right are equal.

    It's clear it is a very different physical quantity from the momentum of inertia, the reason being that one is related to distances from the balance point whereas the other is related to distances squared from the grip.

    This explains why changing the grip weight will affect the balance point while not changing the "head heaviness" feeling of the racket. Another way of seeing that is by adding, let's say, 50g at both ends of the racket. The balance point is not changed but the feeling is now extremely head-heavy (and unplayable...).

    Since different rackets have more or less the same shapes, the balance point is somehow related to the "head-heaviness" feeling, but that's not the actual parameter that matters.

    Hope that helps...
    total so and well described.

    we need to describe rackets in a more precise manner.

    a racket can be head heavy balanced (eg. with a 295mm+ balance point), but still feel light weight because the racket itself has low weight.

  3. #37
    Regular Member visor's Avatar
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    http://www.badmintoncentral.com/forums/showthread.php/123622-Head-weight-an-easier-simpler-appoximation-of-swing-weight
    @
    kwun : @kwun : that's why I don't depend on bp and wt as much anymore. Now I measure head wt.
    Last edited by visor; 02-20-2013 at 01:51 PM.

  4. #38
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    If you really want to measure the moment of inertia, you can do it by making a pendulum out of your racket and measuring the oscillation period... From that period, you can infer the moment of inertia.

    Disclaimer: I just swing the racket in the air and/or play with it to know whether it is head-light or head-heavy! The feeling is the most important in my opinion.

  5. #39
    Regular Member visor's Avatar
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    Quote Originally Posted by Olivier P. View Post
    If you really want to measure the moment of inertia, you can do it by making a pendulum out of your racket and measuring the oscillation period... From that period, you can infer the moment of inertia.

    Disclaimer: I just swing the racket in the air and/or play with it to know whether it is head-light or head-heavy! The feeling is the most important in my opinion.
    yep, that's how swingtool app for iphone works...

    https://itunes.apple.com/us/app/swin...408209116?mt=8


  6. #40
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    There are really apps for everything right now

    The physics in this page about baseball bats is interesting and well explained.
    http://www.acs.psu.edu/drussell/bats/bat-moi.html

    I reckon most of it can be applied to understand badminton rackets.

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