# AS Physics - Mechanics.

All key definitions needed.

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• Created by: EJ
• Created on: 01-05-11 19:57

## Tensile forces.

Usually two equal and opposite forces acting on both ends of a wire in order to stretch it.

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## Compressive forces.

Two or more forces that have the effect of reducing the volume of the object on which they are acting, or reducing the length of a spring.

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## Elastic deformation.

The object will return to its original shape when the deforming force is removed.

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## Plastic deformation.

The object will not return to its original shape when the deforming force is removed, it becomes permanently deformed.

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## Elastic limit.

The point at which elastic deformation becomes plastic deformation.

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## Elastic potential energy.

The energy stored within a stretched or  compressed object (for example a spring).

J

E = work done = 0.5Fx =

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## Extension.

The change in length of an object when subjected to tension.

m

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## Hooke's law.

The extension of an elastic body is proportional to the force that causes it.

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## Stress.

The force per unit cross-sectional area.

Pa

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## Young modulus.

The ration between stress and strain.

Pa

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## Ductile.

Materials that have a large plastic region, therefore can be drawn into wire; for example, copper.

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## Ultimate tensile stress.

The maximum stress that can be applied to an object before it breaks.

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## Ultimate tensile strength.

The maximum tensile force that can be applied to an object before it breaks.

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## Brittle.

A material that distorts very little even when subject to a large stress and does not exhibit any plastic deformation; for example concrete.

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## Strain.

Extension per unit length.

(L change = extension).

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## Polymeric material.

A material made of many smaller molecules bonded together, often making tangled long chains. These materials often exhibit very large strains (e.g. 300%), for example rubber.

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