# Physics AS Materials Unit 2

A set of AS physics revision cards for the materials section of Unit 2. Feel free to download/use them!

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## Hooke's Law

The extension of a spring is directly proportional to the load or force acting upon it.

F = ke

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Mass / Volume

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## Tensile Stress

Force / Cross-sectional Area

Note: Cross sectional area = (pi x diameter^2) / 4

It is measured in Nm^-2 or Pa (Pascals)

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## Tensile Strain

Change in Length / Original Length

It has no units, it is just a number.

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Stress / Strain

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## Elastic Limit

If you increase the force (load) on a material past the Elastic Limit, the material will become permanently elastically deformed, meaning it will no longer return to its original shape.

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## Limit of Proportionality

If you increase the Force (load) on a material past the limit of proportionality, then it will no longer obey Hooke's Law, however it will return to its original shape because the limit of proportionality is reached before the elastic limit.

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## Yield Point

Here the material suffers a large amount of plastic deformation without an extra force (load).

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## If a material is Brittle..

..It snaps suddenly when the force reaches a certain size, without plastically deforming.

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## Energy Stored in a spring/wire

0.5 x stress x strain

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## Ultimate Tensile Stress

The maximum stress a material can withstand.

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