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 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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