# 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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