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# Strain

Strain is a measure of the deformation of an object. simply put: if you apply a force to an object which changes the size of this object, you have put it under strain.

Strain is a dimensionless quantity represented by the greek letter epsilon ($\varepsilon$) it is the percentage change in length of an object. For example:
A rod of length 2 metres is subjected to a force which causes it to expand in length by 5 millimetres, The strain on this rod is simply 0.005/2 = 0.0025 $\varepsilon$

$\varepsilon = \frac{L-L_0}{L_0}$ where L is the length of the rod under a load and $L_0$ is the original length.