- As we know that, all the materials are made from atoms and molecules. When we apply some external force the intermolecular bonding of the atoms gets disturbed and they get deformed. But, at that time also, there is some internal elastic forces will be set up in the body which try to bring the body to its original position.
- The bodies or materials which regains their original shape and size after removal of some external unbalanced force then such bodies are called as elastic bodies.
- And the property is called as elasticity.
- For example: rubber
- And some bodies or materials which are not regains their original shape and size even after removal of the external force such bodies are called as plastic bodies. And such property is called as plasticity.
- For example: clay
- The elastic properties of the bodies are explained on the basis of stress and strain.
- Stress is nothing but the external applied force per unit cross sectional area of the body and is given by,
Stress = applied force/ area
- The SI unit of stress is N/m2.
- And strain of the body is defined as the change in dimensions of the body to the original dimensions of the body.
- And it is given by
Strain = change in dimensions/ original dimensions
- The quantity strain has no units.
Hooke’s law Statement:
According to Hooke’s law, up to an elastic limit the stress acting on a body is directly proportional to the strain of the body.
Explanation:
As stress α strain
We write stress = M strain
Thus, M = stress/strain
Where M is the proportionality constant called as modulus of elasticity.
- The modulus of elasticity has SI unit as N/m2.
- The dimensions of modulus of elasticity are [L-1 M1 T-2].
- The materials which obey Hooke’s law are called as the linear elastic or Hookean materials.