Stress - Definition, Unit, Types, FAQs

Stress - Definition, Unit, Types, FAQs

Team Careers360Updated on 02 Jul 2025, 04:36 PM IST

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.

Commonly Asked Questions

Q: What is stress in physics?
A:
Stress is the internal force per unit area that develops within a material when an external force is applied to it. It represents how the force is distributed throughout the object and is a measure of the material's internal resistance to deformation.
Q: How is stress different from force?
A:
While force is an external influence that can change an object's motion or shape, stress is the internal response of the material to that force. Stress describes how the force is distributed within the object, while force is the external cause of that distribution.
Q: Can stress exist without strain?
A:
No, stress and strain always occur together in real materials. When a force is applied to a material, it experiences both stress (internal force distribution) and strain (deformation). The relationship between stress and strain is described by Hooke's Law for elastic materials.
Q: How does the cross-sectional area affect stress?
A:
Stress is inversely proportional to the cross-sectional area. For a given force, a smaller cross-sectional area will result in higher stress, while a larger area will distribute the force more widely, resulting in lower stress.
Q: How does temperature affect stress in materials?
A:
Temperature can significantly affect stress in materials. Generally, increasing temperature reduces a material's ability to withstand stress. This is because higher temperatures increase atomic vibrations, weakening interatomic bonds and making the material more susceptible to deformation.

What is the unit of stress?

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

So, The SI unit of stress is $\mathrm{N} / \mathrm{m}^2$ (pascal، Pa ).

The CGS unit of stress is dyne/ $\mathrm{cm}^2$.

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Commonly Asked Questions

Q: What is the SI unit of stress?
A:
The SI unit of stress is Pascal (Pa), which is equivalent to one Newton per square meter (N/m²). Larger units like megapascals (MPa) or gigapascals (GPa) are often used for higher stress values.
Q: What is the relationship between stress and pressure?
A:
While both stress and pressure are measured in the same units (force per unit area), they describe different phenomena. Pressure typically refers to the force exerted by fluids on surfaces, while stress describes the internal forces within solid materials in response to external forces.
Q: What is the stress-strain curve?
A:
The stress-strain curve is a graphical representation of the relationship between stress (force per unit area) and strain (deformation) in a material. It shows how a material deforms under different levels of applied stress and is used to determine various mechanical properties of the material.
Q: How does stress relate to material failure?
A:
Material failure occurs when the applied stress exceeds the material's strength. Different types of stress can lead to different failure modes, such as tensile failure (breaking apart), compressive failure (crushing), or shear failure (sliding). Understanding stress distributions helps predict and prevent material failure.
Q: How does stress relate to fatigue in materials?
A:
Fatigue is the weakening of a material caused by repeated cycles of stress, even when the stress is below the material's yield strength. Over time, these stress cycles can lead to the formation and growth of cracks, eventually causing material failure at stress levels lower than its normal breaking point.

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

Tensile Stress

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 meter (N/m²) :

$1 \mathrm{~Pa}=1 \mathrm{~N} / \mathrm{m}^2$

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

B. Shear stress or tangential stress

The figure shows a body being deformed by shear stress. A force acting in a generally horizontal direction especially or force that produces mountain folding and over thrusting.

Shear stress

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.

Bulk stress

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 stress shear 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 $\Delta \theta$. Hence, due to the rise in temperature, there develops a strain which is represented by $\Delta L L$.

From Young's Modulus $Y=$ Stress/Strain
We get, Stress $=Y \times$ Strain $=Y \Delta L / L$.

Relation between Stress and Elastic Potential Energy

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

The relation with stress is,

Elastic Potential Energy

$U=\frac{1}{2}$ Stress $\times$ Strain

Also, check-

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NCERT Physics Notes :

Commonly Asked Questions

Q: What are the main types of stress?
A:
The three main types of stress are:
Q: What is the difference between normal stress and shear stress?
A:
Normal stress acts perpendicular to the surface of a material and can be either tensile (pulling apart) or compressive (pushing together). Shear stress, on the other hand, acts parallel to the surface and tends to cause sliding between adjacent layers of the material.
Q: What is elastic limit?
A:
The elastic limit is the maximum stress a material can withstand while still returning to its original shape when the stress is removed. Beyond this point, the material enters the plastic deformation region and will not fully recover its original shape.
Q: How does stress relate to Hooke's Law?
A:
Hooke's Law states that for small deformations, stress is directly proportional to strain. This relationship is represented by the equation σ = Eε, where σ is stress, E is Young's modulus (a measure of the material's stiffness), and ε is strain.
Q: What is Young's modulus and how does it relate to stress?
A:
Young's modulus (E) is a measure of a material's stiffness or resistance to elastic deformation. It is defined as the ratio of stress to strain in the linear elastic region of the stress-strain curve. A higher Young's modulus indicates that more stress is required to produce a given amount of strain.

Frequently Asked Questions (FAQs)

Q: How does stress affect the behavior of polymers?
A:
Stress can cause various responses in polymers, including viscoelastic behavior (time-dependent deformation), stress relaxation, and creep. It can also induce molecular alignment in some polymers, affecting their properties. At high stresses or strain rates, polymers may exhibit brittle fracture instead of their typical ductile behavior.
Q: How does stress corrosion cracking occur?
A:
Stress corrosion cracking is a form of material failure that occurs when a material is subjected to both stress and a corrosive environment simultaneously. The combination of these factors can lead to the formation and growth of cracks at stress levels below the material's normal yield strength, potentially causing catastrophic failure.
Q: What is the difference between plane stress and plane strain?
A:
Plane stress is a two-dimensional stress state where stress acts only in the plane of the material (like in thin plates), while plane strain occurs when deformation is constrained in one direction (like in thick plates or long cylinders). These concepts are important in simplifying stress analysis for certain geometries.
Q: What is the significance of von Mises stress?
A:
Von Mises stress is a scalar value that combines the effects of all stress components acting on a material. It is particularly useful for predicting yielding of ductile materials under complex loading conditions. When the von Mises stress exceeds the yield strength of the material, plastic deformation is expected to occur.
Q: How does stress wave propagation occur in materials?
A:
Stress waves are disturbances that propagate through a material when it is subjected to sudden loading. These waves travel at the speed of sound in the material and can be longitudinal (compression waves) or transverse (shear waves). Understanding stress wave propagation is crucial in impact analysis and non-destructive testing.
Q: What is the relationship between stress and creep in materials?
A:
Creep is the tendency of a material to slowly deform permanently under constant stress, especially at elevated temperatures. The rate of creep generally increases with higher stress and temperature. Understanding this relationship is crucial for designing components that must maintain their shape under long-term loading at high temperatures.
Q: How does stress affect phase transformations in materials?
A:
Stress can influence phase transformations in materials by changing the thermodynamic stability of different phases. It can alter transformation temperatures, affect the kinetics of phase changes, and even induce new phases. This relationship is important in shape memory alloys and other smart materials.
Q: What is dynamic stress?
A:
Dynamic stress refers to stress that varies with time, as opposed to static stress which remains constant. It can be caused by vibrations, impacts, or cyclic loading. Analyzing dynamic stress is crucial in applications involving moving parts, vibrations, or impact loads, as materials often behave differently under dynamic conditions compared to static conditions.
Q: What is the concept of stress intensity factor?
A:
The stress intensity factor is a parameter used in fracture mechanics to predict the stress state near the tip of a crack. It depends on the applied stress and the crack geometry. When the stress intensity factor reaches a critical value (fracture toughness), the crack will propagate, potentially leading to material failure.
Q: How does residual stress affect material properties?
A:
Residual stress can significantly affect material properties and performance. It can improve fatigue life and stress corrosion resistance if compressive, or reduce these properties if tensile. Residual stress can also cause dimensional changes, affect crack propagation, and influence the overall strength and stiffness of components.

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CBSE's plan for two board exams a year aims to reduce stress, but at the ground level, it creates challenges :

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It sounds like you're looking for ways to manage stress. Here are a few activities that are known to help reduce stress, along with one that generally does not:

  1. Exercise :

  2. Meditation and Mindfulness :

  3. Healthy Eating :

  4. Procrastination :

Stress during exam season is normal. Try to take breaks in between while studying. If it becomes overwhelming, don't hesitate to ask for help from friends, teachers and family members. You can check out the following tips while preparing for the GSEB board exam: