Elasticity - NEET Notes

Introduction to Elasticity

Elasticity is the property of a material by virtue of which it regains its original shape and size when the deforming force is removed. It plays a crucial role in mechanics and material science.

Stress and Strain

Stress is the restoring force per unit area applied on a body, and strain is the relative deformation experienced by the body. Stress is measured in Pascals (Pa), while strain is dimensionless.

Types of Stress

There are three types of stress:

• Tensile Stress: When a material is stretched.
• Compressive Stress: When a material is compressed.
• Shear Stress: When a material experiences parallel forces in opposite directions.

Types of Strain

Strain is categorized into three types:

• Longitudinal Strain: Change in length per unit original length.
• Volumetric Strain: Change in volume per unit original volume.
• Shear Strain: Angular displacement due to shear stress.

Hooke’s Law

Hooke’s Law states that within the elastic limit, stress is directly proportional to strain. Mathematically,

Stress ∝ Strain or σ = E × ε

where E is the modulus of elasticity of the material.

Modulus of Elasticity

It is the ratio of stress to strain and is categorized as:

• Young’s Modulus (Y): Ratio of tensile stress to tensile strain.
• Bulk Modulus (K): Ratio of volumetric stress to volumetric strain.
• Shear Modulus (G): Ratio of shear stress to shear strain.

Elastic Limit and Permanent Deformation

The elastic limit is the maximum stress a material can withstand without permanent deformation. Beyond this limit, the material undergoes plastic deformation.

Applications of Elasticity

Elasticity is widely used in:

• Engineering and construction (e.g., bridges, buildings).
• Manufacturing of springs and shock absorbers.
• Biomechanics (e.g., elasticity of tendons and skin).