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Angular Simple Harmonic Motion

  1. May 13, 2015 #1
    1. The balance spring of a watch is a hoop 1.2 cm in diameter, with a mass of 0.65 g. If the watch is running 45 seconds per day too fast, by what percentage should the rotational inertia of the hoop be changed?

    2. Relevant equations: I = mR^2
    Ia = -k(theta)
    x(t) = Xm Cos(wt + @) (just using @ for phase constant)
    T = 2pi ( I/mgL)^0.5

    3. Rotational inertia = (0.00065 kg) x (0.006)^2 = 2.34 x 10^-8 I actually have no idea where to go from there.
     
  2. jcsd
  3. May 13, 2015 #2

    BvU

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    Hello LC, welcome to PF :smile: !

    You don't want the value of the inertia, you only want the change ! So you could just as well call it ##I_0##, from which you can calculate a ##T_0##. You want a ##T_1## which is soandosmuch over soandso times ##T_0##. That tells you something about ##I_1## in terms of ##I_0## !

    Cryptic ? Give it a try and post.

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