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Finding centre of gravity of a non-uniform rod... help please!

  • 25-02-2008 8:47pm
    #1
    barnesd
    Closed Accounts Posts: 522 ✭✭✭


    A con-rod to be more precise. I know the mass and overall length, the frequency it oscillates at when hung from a particular point and can work out the natural fequency so by 2pi/T. You can get moment of inertia about the centre of mass for a uniform rod but mL^2/12 right? Does this work here too? I know I can get it by m1L1^2 +m2L2^2 too but I don't know any of those things. Anything that could get me started? Been trying for ages, thanks a lot.


Comments

  • #2
    Turbulent Bill
    Registered Users, Registered Users 2 Posts: 1,638 ✭✭✭Turbulent Bill


    Are you trying to find it by measurement or from theory?

    Measurement should be simple, just suspend it from a piece of string - it will be balanced horizontally when suspended from the centre of gravity. Otherwise you'll probably have to get the second moment of area of the complete con-rod by combining the constituent parts, e.g., rod, big end etc. as you said.

    Depending on the dimensions, you might find that most of the mass is concentrated at the end(s), in which case you could treat it as a simple pendulum.


  • #3
    barnesd
    Closed Accounts Posts: 522 ✭✭✭barnesd


    No not from measurement, I'd be fine in that case! I think I've just about figured it out, found it to be just below the big end. Would that make sense?


  • #4
    mawk
    Registered Users, Registered Users 2 Posts: 2,738 ✭✭✭mawk


    yeah it should be just below the big end, its a while since i did this in a mech lab, but my hazy memory says we suspended it by two spring balances giving m1 and m2 and then we worked it out by the formula

    but i cant actually remember what the point of the lab was..:rolleyes:


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