Can someone explain elastic band physics

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SUMMARY

The discussion centers on using a strength training resistance band to create a device that prevents an egg from breaking when dropped from a second-story window. The key formula for modeling the behavior of the band is given by the differential equation m(d²x/dt²) + β(dx/dt) + kx = f(t), where m is mass, β is the damping coefficient, k is the spring constant, and f(t) is the forcing function. The goal is to achieve an over-damped system with the equilibrium position set above the ground level. Experimentation is essential for fine-tuning the device, as theoretical calculations may not yield accurate results.

PREREQUISITES
  • Understanding of basic physics concepts, including mass, force, and motion.
  • Familiarity with differential equations and their application in modeling physical systems.
  • Knowledge of damping coefficients and spring constants in elastic materials.
  • Experience with experimental design and trial-and-error methods in physics projects.
NEXT STEPS
  • Research the principles of over-damping in mechanical systems.
  • Learn how to experimentally determine the spring constant (k) for different materials.
  • Explore the effects of damping coefficients (β) on motion through air.
  • Investigate alternative shock-absorbing materials and their properties for similar applications.
USEFUL FOR

This discussion is beneficial for physics students, educators, and hobbyists interested in experimental mechanics and device design, particularly those working on projects involving shock absorption and material properties.

Pianodude132
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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 until after i unhook the egg at the bottom?
thanks
 
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Pianodude132 said:
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 until after i unhook the egg at the bottom?
thanks

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!
 
thanks very much!
 
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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