# Can someone explain elastic band physics

1. Dec 15, 2016

### Pianodude132

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. Dec 15, 2016

### Student100

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!

3. Dec 15, 2016

### Pianodude132

thanks very much!

4. Dec 17, 2016

### CWatters

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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