Question

A spring balance shows wrong readings after using for a long time . Why ?

Answer 1

This is because of continous usage , the wire loses its elasticity and does not regain its original configuration(this property or phenomenon is known as elastic fatigue ).this is why it shows wrong readings.

The temporary loss of elastic properties because of the action of repeated alternating deforming force is called elastic fatigue. (Because of this only we are able to break a wire by repeated bending.)