# CBSE Class 11th Physics Notes for ​Chapter 9 Mechanical Properties Of Solids

Chapter 9 Mechanical Properties Of Solids

ELASTICITY

Elasticity is a property by the virtue of which the solid regains its original shape once the external force is removed.

PLASTICITY

Plasticity is the property by virtue of which the sold does not regain its original shape even after all the external forces are removed.

DUCTILITY

Ductility is the property of a solid to be drawn into thin wires.

MALLEABILITY

Malleability is the property of a solid to be beaten into thin sheets.

STRESS

Stress is the restoring force per unit area. When we apply an external force on the body to change its shape there is a restoring force that develops in the body in the opposite direction.

Mathematically, Stress = F / A, where F is the restoring force that develops in the body and A is the area. The SI unit of stress is N/m2 or Pascal (Pa).

Types of stress:

• Longitudinal stress: It is defined as the restoring force per unit area when the force is applied to the cross sectional area of the cylindrical body. There are two types of longitudinal stress:
• Tensile stress: When the stress leads to an increase in the length of the body.
• Compressive stress: When the force applied compresses the body.
• Shearing stress: Also known as tangential stress. The restoring force per unit area when the force is applied parallel to the cross sectional area of the body.
• Hydraulic stress: The restoring force per unit area when the force on the body is applied by a fluid.

STRAIN

Strain is a measure of deformation i.e. the displacement between the particles in the body.

Mathematically, Strain= (Change in length)/ (original length)

Types of strain:

• Longitudinal strain: When the change in length occurs due to longitudinal stress.
• Shearing strain: The relative displacement of the opposite faces of the body as a result of shearing stress.
• Volume strain: The ratio of change in volume to the original volume due to hydraulic stress.

HOOKE’S LAW

This law states that within the elastic limit, stress developed is directly proportional to the strain produced in a body.

Mathematically,

Stress = k x strain, where k is the modulus of elasticity

Elastic modulus: It is the ratio of stress and strain.