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Stress - Definition, Unit, Types, FAQs

Stress - Definition, Unit, Types, FAQs

Edited By Team Careers360 | Updated on Jul 02, 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.

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/ $\mathrm{cm}^2$.

Also read -

This Story also Contains
  1. What is Stress?
  2. What is the unit of stress?
  3. Types of Stress
Stress - Definition, Unit, Types, FAQs
Stress - Definition, Unit, Types, FAQs

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

Related Topics,

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-

NEET Highest Scoring Chapters & Topics
This ebook serves as a valuable study guide for NEET exams, specifically designed to assist students in light of recent changes and the removal of certain topics from the NEET exam.
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NCERT Physics Notes :

Frequently Asked Questions (FAQs)

1. Define stress in physics.

Stress meaning in physics, is the amount of force that acts on any material with unit surface area. It is the property by which we can understand the limit of deformation of any material.

2. What is the SI unit of stress?

The SI unit of stress is Nm2. The SI unit of stress is also considered to be Pascal.

3. What is the SI unit of stress?
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.
4. What are the different types of stress?

There are mainly three types of stress in physics-

  1. Tensile stress or Normal stress: Tensile stress or normal stress is defined as the stress, when the force F acts normal to the surface of the material to a cross-sectional area A. The formula of tensile or normal or longitudinal stress is, Normal stress=FA. Normal stress is also known as longitudinal stress.

  2. Shear Stress or Tangential stress: Shear stress or tangential stress is defined as the stress where the forces F act tangentially to the opposite ends of an object of surface area A. The formula of shear or tangential stress is, Tangential Stress=FA.

  3. Bulk stress or Volumetric stress: Bulk stress or volume stress is defined as the force which acts tangentially on the surface of a body which causes a change in its volume or pressure. This stress symbol is, ∆p where p is pressure which can be written as p=F/A.

5. What is hoop stress formula?

The hoop stress formula is H=PDm/2t where, H= hoop stress, P = pressure, t = thickness of the pipe and Dm = diameter of the pipe.

6. What are the main types of stress?
The three main types of stress are:
7. What is the difference between normal stress and shear stress?
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.
8. What is elastic limit?
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.
9. How does stress relate to Hooke's Law?
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.
10. What is Young's modulus and how does it relate to stress?
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.
11. What is stress in physics?
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.
12. How is stress different from force?
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.
13. Can stress exist without strain?
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.
14. How does the cross-sectional area affect stress?
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.
15. How does temperature affect stress in materials?
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.
16. What is the relationship between stress and pressure?
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.
17. What is the stress-strain curve?
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.
18. How does stress relate to material failure?
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.
19. How does stress relate to fatigue in materials?
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.
20. How does stress distribution change in composite materials?
In composite materials, stress distribution is more complex due to the presence of different materials with varying properties. The stress is typically not uniform and depends on the properties and arrangement of the constituent materials. This non-uniform distribution can lead to unique failure modes and requires careful analysis.
21. How does stress affect the magnetic properties of materials?
Stress can significantly affect the magnetic properties of materials through a phenomenon called magnetostriction. Applied stress can change the magnetic domain structure in ferromagnetic materials, altering their magnetic behavior. This relationship is used in various sensors and actuators.
22. How does stress affect the electrical properties of materials?
Stress can alter the electrical properties of materials through various mechanisms. In semiconductors, stress can change the band structure, affecting conductivity. In piezoelectric materials, stress directly generates an electric field. These effects are utilized in strain gauges and other sensing devices.
23. How does stress distribution change near a crack tip?
Near a crack tip, stress distribution becomes highly non-uniform, with stress concentration occurring at the tip. This localized high stress can lead to crack propagation even when the overall stress in the material is below its yield strength. Understanding this stress distribution is fundamental to fracture mechanics and predicting material failure.
24. What is stress shielding and why is it important in biomaterials?
Stress shielding occurs when an implant (like a bone implant) carries a larger portion of the load, reducing the stress experienced by the surrounding tissue. This can lead to bone resorption and weakening. Understanding and mitigating stress shielding is crucial in designing effective and long-lasting biomedical implants.
25. What is the concept of stress triaxiality?
Stress triaxiality is a measure of the hydrostatic stress component relative to the equivalent stress in a material. It plays a crucial role in ductile fracture mechanics, affecting the material's ductility and fracture behavior. High stress triaxiality can lead to void nucleation and growth, potentially causing ductile fracture at lower strains.
26. How does stress affect the thermal conductivity of materials?
Stress can influence the thermal conductivity of materials by altering their atomic or molecular structure. In metals, stress can increase electron scattering, reducing thermal conductivity. In some materials, stress-induced changes in crystal structure or defect concentration can significantly affect heat transfer properties. This relationship is important in thermal management applications and in understanding the behavior of materials under extreme conditions.
27. Can stress be negative?
Yes, stress can be negative. Negative stress typically refers to compressive stress, where the forces are pushing the material together. Positive stress usually indicates tensile stress, where forces are pulling the material apart.
28. What is the difference between engineering stress and true stress?
Engineering stress is calculated using the original cross-sectional area of the material, while true stress uses the instantaneous cross-sectional area during deformation. True stress is more accurate, especially for large deformations, but engineering stress is often used for simplicity in calculations.
29. What is residual stress?
Residual stress is stress that remains in a material even after the external forces have been removed. It can be caused by manufacturing processes, heat treatment, or plastic deformation. Residual stress can affect a material's performance and lifespan.
30. How does stress concentration occur?
Stress concentration occurs when the geometry of an object causes an intensification of stress in a localized area. This often happens at sharp corners, holes, or sudden changes in cross-sectional area. Stress concentration can lead to material failure at lower overall stress levels than expected.
31. What is the difference between ductile and brittle failure under stress?
Ductile failure occurs when a material undergoes significant plastic deformation before fracturing, often showing necking or thinning. Brittle failure, on the other hand, occurs suddenly with little or no plastic deformation. The type of failure depends on the material properties and the nature of the applied stress.
32. What is thermal stress?
Thermal stress is internal stress induced in a material due to temperature changes. It occurs when different parts of a material expand or contract at different rates, or when the material's expansion is constrained. Thermal stress can lead to material deformation or failure if not properly managed.
33. How does stress affect the atomic structure of materials?
At the atomic level, stress causes atoms to move relative to each other. In the elastic region, these movements are small and reversible. As stress increases, it can cause permanent shifts in atomic positions (plastic deformation) or even break atomic bonds, leading to material failure.
34. What is the significance of yield stress?
Yield stress is the point at which a material begins to deform plastically. It marks the transition from elastic to plastic behavior and is a crucial parameter in material selection and design. Beyond the yield stress, a material will not fully return to its original shape when the stress is removed.
35. What is the principle of superposition in stress analysis?
The principle of superposition states that the total stress in a material subjected to multiple forces is the sum of the stresses caused by each force acting independently. This principle is valid for linear elastic materials and allows for the analysis of complex stress states by breaking them down into simpler components.
36. How does Poisson's ratio relate to stress?
Poisson's ratio is the negative ratio of transverse strain to axial strain in a material under stress. It describes how a material expands in directions perpendicular to the direction of compression, or contracts in directions perpendicular to the direction of extension. This ratio affects how stress is distributed in three dimensions within a material.
37. What is the difference between hydrostatic stress and deviatoric stress?
Hydrostatic stress is the component of stress that tends to change the volume of a material without changing its shape. Deviatoric stress, on the other hand, tends to change the shape of a material without changing its volume. The total stress in a material can be decomposed into these two components.
38. How does stress relate to strain energy?
Strain energy is the energy stored in a material as it deforms under stress. In the elastic region, this energy is recoverable and is proportional to the square of the stress. The area under the stress-strain curve represents the strain energy per unit volume of the material.
39. What is stress relaxation?
Stress relaxation is the decrease in stress over time in a material held at constant strain. It occurs due to the rearrangement of atoms or molecules within the material, often more pronounced at higher temperatures. This phenomenon is important in applications where materials are subjected to constant deformation over long periods.
40. What is the concept of principal stresses?
Principal stresses are the maximum and minimum normal stresses acting on a material at a given point. They occur on planes where there is no shear stress. Understanding principal stresses is crucial for analyzing complex stress states and predicting material behavior under various loading conditions.
41. How does stress corrosion cracking occur?
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.
42. What is the difference between plane stress and plane strain?
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.
43. What is the significance of von Mises stress?
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.
44. How does stress wave propagation occur in materials?
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.
45. What is the relationship between stress and creep in materials?
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.
46. How does stress affect phase transformations in materials?
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.
47. What is dynamic stress?
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.
48. What is the concept of stress intensity factor?
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.
49. How does residual stress affect material properties?
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.
50. What is the difference between isotropic and anisotropic stress?
Isotropic stress is uniform in all directions, while anisotropic stress varies with direction. Most materials exhibit some degree of anisotropy in their response to stress, especially composite materials and single crystals. Understanding this difference is crucial for accurately predicting material behavior under complex loading conditions.
51. How does stress affect the optical properties of materials?
Stress can alter the optical properties of materials through the photoelastic effect. This causes changes in the material's refractive index, leading to birefringence (double refraction). This phenomenon is used in photoelastic stress analysis and in some optical components like wave plates.
52. What is the concept of equivalent stress?
Equivalent stress is a scalar value that represents the overall stress state in a material subjected to multiple stress components. It allows for the comparison of complex stress states to simple uniaxial stress states. The von Mises stress is a common form of equivalent stress used in failure prediction for ductile materials.
53. How does stress affect the diffusion of atoms in materials?
Stress can significantly influence atomic diffusion in materials. Tensile stress tends to increase diffusion rates by increasing the spacing between atoms, while compressive stress typically decreases diffusion. This relationship is important in understanding phenomena like creep, stress corrosion, and certain heat treatment processes.
54. How does stress affect the behavior of polymers?
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.

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Shubham Jha 13 June,2025
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Hello there,

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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  4. Logistical Issues – Managing two national exams adds strain on CBSE and schools.

Without proper planning, this move may increase stress rather than reduce it.


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I understand the situation, and it is indeed possible to attempt your Class 12 exams, even if there has been less attendance due to medical issues. Here's what you can do:

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Act fast and talk to your school authorities to ensure you meet all the requirements.

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