Question

In which year Robert Hooke presented his law of elasticity?
A) $1672$
B) $1674$
C) $1676$
D) $1678$

Answer 1

Hint: A hard-solid object having a definite shape and size is known as a Rigid body. But a rigid body can be stretched, compressed, and bent when a sufficiently large external force is applied to it. This applied external force is called the deforming force.

Complete step by step answer:
When an external force is applied to a body, if the body suffers a change in length, volume, or shape, the body is said to be deformed. When the rigid body is deformed, a restoring force is developed internally which opposes the deforming force. When the body is in equilibrium in the determined state, the internal restoring force is equal and opposite to the external deforming force.
As soon as the deforming force is removed the internal restoring force makes the body recover to its original length, volume, and shape. This property of the material of the body by virtue of which the body regains its original dimension after the removal of deforming force is called elasticity.
An elastic body can regain its original form completely when the deforming force does not exceed a particular limit. This upper limit of the deforming force for which the body can regain its original form is called the elastic limit.
Stress is defined as the internal restoring force developed per unit area of the deforming body.
Under the action of deforming force, the configuration of a body changes, and the body is said to be strained by the force.
In the year 1676, Robert Hooke presented his law of elasticity called Hooke’s law. Which gives the relation between stress and strain that is, for an applied force there is a change in its configuration with an inelastic limit.
Hooke’s law states that, within an elastic limit, the stress is directly proportional to the stress.
That is,
$stress \propto strain$
$ \Rightarrow stress = k(strain)$
$ \Rightarrow k = \dfrac{{stress}}{{strain}}$
Where, $k$ is called modulus of elasticity.

$\therefore $ The correct option is (C).

Note:
- Elastic limit is the property of a body whereas elasticity is the property of a material.
- SI unit of stress is $N{m^{ - 1}}$
- The strain is a dimensionless quantity and has no unit, because the strain meter by meter gets canceled out.
- Robert Hooke discovered that law of elasticity in 1660 but he presented that in 1676.