If an elastic material is stretched or
compressed beyond a certain limit, it will not regain its original state and
will remain deformed. The limit beyond which permanent deformation occurs is
called the elastic limit.
English Physicist Robert Hooke (1635 - 1703) in the year 1676 put
forward the relation between the extension produced in a wire and the restoring
force developed in it. The law formulated on the basis of this study is known
as Hooke's law. According to Hooke's law, within
the elastic limit, strain produced in a
body is directly proportional to the stress that produces it.
(i.e) stress α strain
Stress / Strain = a constant,
known as modulus of elasticity.
Its unit is N m-2
and its dimensional formula is ML-1T-2
Experimental verification of Hooke's law
A spring is suspended from a
rigid support as shown in the Fig.. A weight hanger and a light pointer is
attached at its lower end such that the
pointer can slide over a scale graduated in millimeters. The initial reading on
the scale is noted. A slotted weight of m
kg is added to the weight hanger and the pointer position is noted. The same
procedure is repeated with every additional m
kg weight. It will be observed that the extension of the spring is proportional
to the weight. This verifies Hooke's law.