Forces and Elasticity

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Forces and Elasticity

  • work done to an elastic object is stored as Elastic Potential Energy:
  • applying force to an object may cause it to change shape or stretch - any object that can go back to the original shape after the force has been removed is an elastic object
  • work is done to an elastic object to change its shape, the energy is not lost but stored by the object as elastic potential energy
  • the elastic potential energy is converted to kinetic energy when the force is removed and the object returns to its original shape 
  • extension of an elastic object is directly proportional to the force:
  • the extension, e, of an elastic object is directly proportional to the load or force applied, F
  • F = k x e    = force applied, newtons = spring constant, N/m x extension, metres
  • k is the spring constant, its value depends on the material stretched. 
  • this stops working when the force is great enough:   there is a limit to the amount of force you can apply to an object for the extension to keep increasing proportionally.
  • for small forces - force and extension are proportional
  • there is a max force the elastic object can take and extend proportionally = limit of proportionality, on a graph marked P. 
  • increasing the force past the limit of proportionality = the material is permanently stretched.
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Power

  • power is the rate of doing work 
  • power is not the same as force or energy. 
  • P = E/t    = power, watts = work done(or energy transferred), joules/ time taken, seconds
  • Calculating Power Output:
  • a - the timed un upstairs - "energy transferred" is the potential energy you gain(=mgh) ...   power = mgh/t
  • b - the timed acceleration - energy transferred is the kinetic energy you gain(=mgh) ...       power = 1/2mv(2)/t
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