Strain gauges : ELECTRICAL INSTRUMENTATION SIGNALS. If a strip of conductive metal is stretched, it will become skinnier and longer, both changes resulting in an increase of electrical resistance end-to-end.
Conversely, if a strip of conductive metal is placed under compressive force (without buckling), it will broaden and shorten. If these stresses are kept within the elastic limit of the metal strip (so that the strip does not permanently deform), the strip can be used as a measuring element for physical force, the amount of applied force inferred from measuring its resistance. Such a device is called a strain gauge. Strain Gages, Accessories and Instrumentation: General Purpose Strain Gages. Strain Gages for Stress Analysis. Linear Strain Gauges Record strain in the direction in which their measuring grids are aligned.
One possible application is determining the modulus of elasticity on tension and compression bars.