Thus, if a rod which has an original length L is caused to stretch by an amount l by the action of a force on it, then the strain, or proportionate change of length, in the rod will be e, let us say, such that: To return to our string, if the original length of the string was, say, 2 metres (or 200 cm), and the weight of the brick causes it to stretch by 1 centimetre, then the strain in the string is:
