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Can someone explain elastic band physics

  1. Dec 15, 2016 #1
    in my physics class we have to create a device that will make an egg not break after being dropped from a second story window. my idea was to take a strength training resistance band and use it like a bungee jumping cord and have the egg drop to the bottom without breaking.
    what are the formulas for this?
    can i have the band weighed down so it doesn't spring back up untill after i unhook the egg at the bottom?
    thanks
     
  2. jcsd
  3. Dec 15, 2016 #2

    Student100

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    You can approximate the bungee cord as a spring and somewhat model it's behavior with ##m\frac{d^2x}{dt^2} + \beta \frac{dx}{dt} +kx = f(t)##. Where m is the mass, ##\beta## is the damping coefficient, k is the spring constant, and f(t) would be the forcing function. k is ## \frac {F}{s} = k## which you can determine experimentally. ##\beta## will depend both on the material you use and the damping effect as the system moves through air. x will be the displacement. f(t) will be zero in this case.

    So you basically want to create it so that the system is over-damped, and the equilibrium position is somewhere off the ground of the drop sight. I wouldn't try to calculate this, as the simple model above isn't going to be accurate enough, basically you're going to want to do a lot of trial and error experimentation.

    Make sure you wear goggles when playing around, don't want to lose an eye!
     
  4. Dec 15, 2016 #3
    thanks very much!
     
  5. Dec 17, 2016 #4

    CWatters

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    You could also use a length of string with a short length of elastic to absorb the shock when the string becomes tight.
     
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