Stress - Definition, Unit, Types, FAQs

What is Stress?

Stress definition is, the force that acts on a body of per unit area. The effect of stress causes strain in the material. Stress is the process which helps to deform the material. Stress in physics, helps us to understand the force that a material or object experiences.

What is the unit of stress?

Stress meaning, the force that acts on a material in a unit area.

So, the unit of stress is,

Stress=ForceArea=Nm2

Hence, we get the SI unit of stress is Nm2 and in cgs unit of stress is dynecm2.

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Types of Stress

A. Tensile Stress or Normal Stress

The tensile stress definition is given below-

The external force per unit area of material resulting in stretch of material is known as tensile stress. We say that object is in tension. The subscript is a reminder that force acts perpendicular to cross-section.

We define tensile stress at cross-section as ratio of force F to cross-sectional area A:

Normal stress=FA----(1)

This is a scalar quantity. The SI unit of stress is pascal. Equation (1) shows that 1 pascal equals 1 newton per square metre (N/m²) :

1 pascal = 1 Pa = 1 N/m²

The unit of stress is same as that of pressure. Air pressure in automobile tyres is typically around 300 kPa.

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B. Shear stress or tangential stress

Figure shows a body being deformed by shear stress. A force acting in generally horizontal direction especially or force that produces mountain folding and overthrusting.

Shear stress or Tangential stress=FA.

C. Bulk stress or Volumetric stress

Thus, bulk stress or volume stress is also can be called as pressure.

Bulk stress or Volume stress=p=FA.

Hooke’s Law

Hooke’s Law is defined as the ratio of stress to strain.

StressStrain=Hooke's Law (Elastic Modulus)

The relation between stress and modulus of elasticity:

1. Young's Modulus Y=Tensile stress or Normal stressTensile strain or normal strain
2. Shear Modulus G=Shear stress or tangential stressShear strain or tangential strain
3. Bulk Modulus B=Normal stressVolume strain

Thermal stress

The stress which is developed due to the rise or fall in temperature is known as thermal stress.

Let us consider that a rod of length L is fixed between two rigid walls and is heated to raise the temperature by ∆θ . Hence, due to rise in temperature, there develops a strain which is represented by ∆LL.

From Young’s Modulus Y=Stress/Strain

We get, Stress=Y×Strain=Y∆L/L.

Relation between Stress and Elastic Potential Energy

Elastic Potential energy is defined as total work which is done against the restoring force that stretches a material by any length.

The relation with stress is,

Elastic Potential Energy U=12Stress×Strain

Also check-

• NCERT Exemplar Class 11th Physics Solutions
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NCERT Physics Notes :

• NCERT Notes class 11 physics
• NCERT Notes class 12 physics
• NCERT Notes for all subject