How to test tennis balls (measuring bounce)

Discussion in 'Other Equipment' started by stoneage, May 25, 2011.

  1. stoneage

    stoneage Rookie

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    According to the ITF rules a "valid" tennis ball should bounce to between 135 cm and 147 cm when dropped on a concrete floor from a height of 254 cm (53-57 in from 100 in). This means that the ball should reach between 53% and 57% of the drop height when bouncing. However, that is a little difficult to measure, unless you have a high speed camera and are prepared to spend some time analyzing the video. Probably not something worth doing for checking and old can of balls.

    A simpler way is to use the sound and a basic laws of physics. If you drop the ball and measure the time "t" between the first impact on the floor and the second, you can calculate the height "h" the ball has reached through the equation (g is gravity):

    h=g*t^2/8

    If you want to be more precise you can include the air resistance, which is fairly small, but will reduce the height with about 3 %. So including that and g=9.81 you get:

    h= 1.19*t^2

    Since you take the square of the time you have to measure it fairly exactly. The easiest way to do it, is to record the sound with a computer, and get the time between the two bumps in the sound curve. Agreed that this still is a little work, but nothing that should prevent a scientifically minded tennis nerd :)

    I have implemented this and some further calculation to handle low bounces in the latest version of racquetTune.

    /Sten

    ______________________________________
    racquetTune, swingTool and netHeight, tennis apps for the iPhone.
     
    #1
  2. mikeler

    mikeler G.O.A.T.

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    You are going to put low bouncing Penn balls out of business! :twisted:
     
    #2
  3. bigmalik76

    bigmalik76 Rookie

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    :) But Penn Balls are cheap at Costco maybe they will get cheaper :)
     
    #3
  4. vandre

    vandre Hall of Fame

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    dude, you're making me want an iphone! curse you!

    i'm a caveman i guess, because i test the bounce of a tennis ball by holding it at eye level and dropping it. if it bounces to or above my waist, it's good.
     
    #4
  5. The Matrix

    The Matrix New User

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    Are you really going to do this just to see how dead a ball is??
     
    #5
  6. bigmalik76

    bigmalik76 Rookie

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    I'll rather open a new can then sit down and solve those equations. (Disclaimer: not a big fan of Math :twisted:)
     
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  7. tennytive

    tennytive Semi-Pro

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    ^^^^ Bingo!
     
    #7
  8. Readers

    Readers Semi-Pro

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    I honestly think it's easier to put a line on a wall or a post, then bounce the ball next to it... takes less than a min.
     
    #8
  9. ae695

    ae695 Rookie

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    Racquettune

    If you have an iPhone (do not know if there is an Android version) you can use Raquettune app. The last version has a ball test.

    Good luck!!
     
    #9
  10. verbouge

    verbouge Rookie

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    The Ball Bounce feature has disappeared from my Racquettune app!

    I was going to show it to someone last night, and lo and behold, it's no longer on the app. Anybody else have this issue? Stoneage, you have any insight or help?

    Thanks,
    Dave in Oregon
     
    #10
  11. LeeD

    LeeD Bionic Poster

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    I'd say any Dunlop bounces the lowest.
    And what air temps? Balls and air temps. In 120 degrees, with heated balls, anything is too bouncy.
    In 39 degrees, even Wilsons are dead as doornails.
     
    #11
  12. tennisnj

    tennisnj Professional

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    It all depends on court surface because the courts I play most of the time are the slowest hardcourts I've ever been on & also the lowest bouncing (they weren't laid right). They play as slow as clay with the bounce of grass courts. The only way to get any pace or depth is to use Dunlop because they bounce the highest.
     
    #12
  13. LeeD

    LeeD Bionic Poster

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    Wait, are you saying Dunrocks bounce the HIGHEST? Higher than Wilson air balls?
    Are you sure this is what you meant to say?
    I hope you don't think Tretorn pressureless also bounce really high?
     
    #13
  14. tennisnj

    tennisnj Professional

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    Again Lee, it all depends on the courts. Tretorns don't bounce @ all where I play & they ruin your arm. The ultra-slow hardcourts I play on don't allow for Penns to be used unless that's all we have handy. The Dunlops bounce the HIGHEST b/c they are the liveliest tennis balls for the courts we play on. Wilsons bounce 'in the middle' if we're comparing Penn, Wilson & Dunlop.
     
    #14
  15. LeeD

    LeeD Bionic Poster

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    Wow, that doesn't go on West Coast cement at all.
    Wilson's are the lightest and most air, least knapp, bouncing highest regardless of court surface.
    Penn's have more knapp, some are heavier.
    Dunlops are what some guys here call "dunrocks", the most knapp, the heaviest, and moderate air pressure.
    Tretorns are the rock, bounce the least, are the heaviest.
     
    #15
  16. tennisnj

    tennisnj Professional

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    I figured it out---many courts on the east coast are more cushioned (not always on purpose-ours happen to be installed incorrectly & there is always a layer of water underneath the 1st few layers.) You may be familiar with the old San Jose ATP tournament the SAP Open; we supposedly use the same surface as there---Premier Court its called http://www.premiercourt.com/what_is.htm & it is god awful. Says it's not a gritty court surface but judging by the way balls look after 5 sets of doubles, I'd say they're very gritty.
     
    #16
  17. JW10S

    JW10S Hall of Fame

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    Oh please--you have to be kidding. I can easily see if a ball bounces a little more than 1/2 way back up when I drop it--besides it's easier just to squeeze them to tell if they're dead or not. You have WAY too much time on your hands--maybe you should spend more time actually playing tennis.
     
    Last edited: Nov 17, 2012
    #17
  18. scotus

    scotus Legend

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    There's nothing "Stone Age" about this guy.
     
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  19. leafscat

    leafscat Rookie

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    The developer made it a stand alone app. It is called Ball Tester and is free (or was). He expanded it a bit as it will also test if basketballs or soccer (footballs) have enough air in them.
     
    #19
  20. sundaypunch

    sundaypunch Hall of Fame

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    Or I could just put three marks on my garage wall and drop the ball.
     
    #20
  21. tennis_ocd

    tennis_ocd Hall of Fame

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    do you take into account humidity and air density? altitude above sea level and its effect on gravity? your latitude and the inertia produced as a result of earth's rotation? Also in play would be the counter gravitational pull of the sun and moon depending on their position relative to earth's orbit and the time of your ball test.

    My guess is you're just winging it and it's holding you back from true GOAT.
     
    #21

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