# A-level Physics/Forces and Motion/Deformation of solids

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## Hooke's law[edit]

This applies to an object's deformation only before the elastic limit; from then on it deforms plastically and no longer follows this law. it states that,extention is directly propotional to the applied force.

## Spring Constant[edit]

The gradient refers to the gradient of a Tension-Extension graph.

The standard units of k are N m^{-1}

## Strain[edit]

Because this is a division of two measurements of length, Strain has no units and remains a ratio.

## Stress[edit]

The units for Stress are N m^{-2}, otherwise known as Pascals (Pa)

## The Young's modulus[edit]

## Strain energy[edit]

However, due to Hooke's Law, it can be calculated in another form;