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# P1.2 - Work & Energy

### Work & Energy - OCR AS Physics

Define work done: Work done = force x distance moved in the direction of the force
Define power: Work done per second.
What is the principle of conservation of energy? Energy cannot be created or destroyed. It can only be converted from one form to another.
How do you work out efficiency? Useful output/total input x 100%
What do sankey diagrams show? Energy input and output.
What does Hooke's law state? Extension is proportional to force.
What is the equation for hook's law? F = ke
When does hooke's law stop working? When the load is great enough, the elastic limit. If you increase the load past the elastic limit the material will be permanently deformed.
What is an elastic stretch? The material will return to it's original shape once the forces are removed.
What is a plastic stretch? The material will be permanently stretched.
A stress causes a ...... A stress causes a strain.
How do you work out the stress of an object? Force/Area
How do you work out the strain of an object? extension/original length
If af stress is big enough to break the material, what is it called? The Breaking Stress. The atoms are completely separated.
What is elastic strain energy? The energy stored in a stretched material. This is given by the area under a force-extension graph.
What equation gives the energy stored in as stretched wire? 1/2 x Force x extension OR 1/2 x k x extension^^2
How do you work out young's modulus? Stress/Strain. It is also equal to the area under a stress/strain graph.
What does the stress strain graph for a ductile material look like? It will curve.
What does the stress strain graph for a brittle material look like? It is a straight line so will not curve.
Rubber will return to it's original length when the load is removed, what is this behaviour called? Elastic Behaviour.
Created by: Sparksy