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Difference Between Stress and Pressure - A Complete Guide

Difference Between Stress and Pressure - A Complete Guide

Edited By Team Careers360 | Updated on Jul 02, 2025 04:46 PM IST

In this article, we will explore stress, pressure, the difference between stress and pressure, and much more. These two terms, stress and pressure, are often used interchangeably, yet they have distinct definitions. Pressure is defined as the amount of force applied per unit area, while stress refers to the force exerted per unit area that a material experiences internally. Understanding the difference between stress and pressure will help clarify their fundamentals and their unique applications.

This Story also Contains
  1. What is the Definition of Stress?
  2. What is Pressure?
  3. What is the Difference Between Stress and Pressure?
Difference Between Stress and Pressure - A Complete Guide
Difference Between Stress and Pressure - A Complete Guide

What is the Definition of Stress?

Stress is a response within a material to restore its original shape and size when deformed. This force, known as the restoring force, acts in opposition to the deforming force. Therefore, stress is defined as the restoring force per unit area within the material. As a tensor quantity, it effectively describes stress and pressure differences in material behaviour.

Background wave

Stress Formula

Stress is defined as a force per unit of area within a material caused by externally applied forces. It accurately describes and predicts flexible elastic, plastic, and fluid behaviour. Stress formula (σ) is given by

σ=FA

The units for stress depend on force and area measurements. The SI unit of stress is the pascal (Pa), or Nm2, which aligns with pressure in stress calculations.

Types of Stress

In physics, there are various types of stress, however, they are primarily divided into two types: normal stress and tangential or shearing stress. The next sections go over some of the different types of stress.

i) Normal Stress: Normal stress is the one in which the direction of the applied force is normal to the cross-sectional area of the body, stress is said to be normal stress. The stress will be normal as the length of the wire or the volume of the body changes. Normal stress is further divided into two types based on the force dimension. Longitudinal stress Bulk stress, also known as volumetric stress

ii) Longitudinal Stress: Consider the shape of a cylinder.

When two cross-sectional sections of the cylinder are exposed to equal and opposite forces, it undergoes stress. The stress is called a longitudinal stress. Deforming Force / Area of Cross-section = F/A = Longitudinal Stress

The Longitudinal Stress stretches or compresses the thing along its whole length. As a result, based on the direction of deforming force, it can be further categorised into two types:

Tensile stress

Compressive stress

a) Tensile Stress: Tensile stress is defined as stress that occurs when a deforming force or applied force causes an increase in the length of an object. For example, a rod or wire can be stretched by drawing it at both ends with equal and opposite forces (outwards).

b) Compressive Stress: When a deforming force or applied force causes an object's length to shrink, the resulting tension is known as compressive stress. When a rod or wire is compressed/squeezed by pulling it inwards with equal and opposite forces at both ends, for example.

iii) Bulk Stress or Volume Stress

When a deforming force or applied force acts on an object in all dimensions, causing a change in volume, this is referred to as volumetric stress or bulk stress. Volume stress occurs when the volume of a body changes as a result of a deforming force.

iv) Shearing Stress or Tangential Stress

When the applied force is parallel to the cross-sectional area of the object then the stress is called shearing stress or tangential stress. The body's shape changes as a result of this.

What is Pressure?

Pressure is the force exerted per unit area perpendicular to an object's surface, with the pascal (Pa) as its SI unit:

P=FA
This formula illustrates that pressure rises with decreased area, explaining stress and pressure differences in applications.

where P denotes the pressure, F denotes the thrust force and A represents the area.

Pressure reduces when the area increases and pressure builds up when the area decreases. The greater the pressure on a surface, the smaller the area. In honour of Blaise Pascal, the S.I. unit of pressure is named the Pascal (Pa). Therefore, 1Pa=1Nm2

1 pascal is described as the pressure exerted on a 1m2 surface by a 1 N thrust acting on it.

Different Types Of Pressure

Pressure is classified as follows

  • Absolute Pressure: It's a sort of pressure that uses a vacuum or an airless environment as a reference point. Because atmospheric pressure differences alter as the location changes, this sort of pressure varies as well. It eliminates the reference to variable ambient pressure and depends on a defined pressure range for reference by employing a device like an absolute pressure sensor.
  • Gauge Pressure: The difference between absolute and atmospheric pressure is known as gauge pressure. Relative pressure is another name for gauge pressure. At sea level, the observed pressure is compared to the standard atmospheric pressure. The vent on pressure sensors used to measure gauge pressure allow the instrument to use ambient pressure as a reference point. Both positive and negative values can be assessed. Overpressure is the term for positive values. Under pressure or partial vacuum occurs when the gauge pressure measurement is negative.
  • Differential Pressure: Differential pressure is the difference between two pressures and is a sort of gauge pressure. It aids in determining the pressure difference between two places. Flow and level measurement applications use differential pressure. The suffix "d" is used to represent differential pressure.
  • Sealed Pressure: The vacuum is defined as a space with no absolute pressure. Perfect vacuum is difficult to obtain in practice and only exists as a theoretical value. A vacuum is generated when the pressure is lower than the atmospheric pressure. In practice, the vacuum will only be attained partially, which is referred to as a partial vacuum.
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A high vacuum indicates a very low absolute pressure. The pressure is measured in a sealed chamber that is kept at atmospheric pressure. The sealed sensor is used to measure the sealed pressure and is made out of an airtight sensing element that prevents further pressure changes owing to changes in ambient conditions. Pressure transducers are protected from damage by sealed pressure. Now let's talk about stress vs pressure in which we are going to see the stress and pressure difference

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What is the Difference Between Stress and Pressure?

Here's the Difference Between Stress and Pressure

Stress
Pressure
Stress is defined as the internal resistive force to deformation per unit area.
Pressure is defined as the amount of force applied per unit area.

(strain) / (Young's modulus) can be used to represent stress.
Pressure can be expressed mathematically as (force) / (area)
Stress is a material characteristic.
Pressure is a distinctive feature of thermodynamics or physics.
Stress can be viewed as either a beneficial or negative force.
The force of pressure is always a positive force.
There is no stress measurement instrument (not a measurable quantity).
Strain or elongation are used to calculate stress.
Pressure gauges, manometers, and other pressure-measuring equipment or instruments are used to physically measure (measure) the pressure.

Tensile, compressive, and shear stress are all possible.
Compressive pressure is constantly present.
The level of tension at a different place in a different direction varies.
The magnitude of pressure at a location remains constant in all directions.
The stress fluctuates as the surface area changes.
The pressure is unaffected by the size of the contact surface.
It remains constant and does not change while the surface area changes.
Internal stress develops.
External pressure is exerted

Understanding what is the difference between stress and pressure and their calculations allows us to distinguish stress vs pressure for practical and scientific applications.

Frequently Asked Questions (FAQs)

1. What is the definition of stress?

Stress is defined as the amount of restoring force per unit of area. 

2. What is the stress unit?

The unit of stress is the pascal (N/m2). 

3. What effect does deforming force have?

The deforming force might alter the object's shape, volume, or size. 

4. In the case of shearing stress, what is the direction of the deforming force?

The deforming force is parallel to the cross-sectional area.

5. What is the difference between stress and pressure in physics?

Stress is defined as the internal resistive force to deformation per unit area.

Pressure is defined as the amount of force applied per unit area. 

(strain) / (Young's modulus) can be used to represent stress. 

Pressure can be expressed mathematically as (force) / (area) 

Stress is a material characteristic. 

Pressure is a distinctive feature of thermodynamics or physics. 

Stress can be viewed as either a beneficial or negative force. 

The force of pressure is always a positive force. 

There is no stress measurement instrument (not a measurable quantity). 

Strain or elongation are used to calculate stress. 

Pressure gauges, manometers, and other pressure measuring equipment or instruments are used to physically measure (measure) the pressure.

Tensile, compressive, and shear stress are all possible. 

Compressive pressure is constantly present. 

6. Can you explain why a sharp knife cuts more easily than a dull one in terms of stress and pressure?
A sharp knife concentrates the applied force over a very small area at its edge, creating high pressure and stress at the point of contact. This localized high stress easily exceeds the material's strength, causing it to separate. A dull knife spreads the force over a larger area, reducing the pressure and stress, making cutting more difficult.
7. What is the relationship between pressure, force, and area, and how does this differ for stress?
The relationship between pressure, force, and area is given by the equation P = F/A, where P is pressure, F is force, and A is area. This same relationship applies to stress, but stress refers to internal forces within a material, while pressure typically refers to external forces applied to a surface.
8. Can you explain why standing on ice with ice skates is more likely to break the ice than standing with boots?
This scenario illustrates the difference between stress and pressure. The person's weight (force) remains the same, but the area of contact changes. Ice skates have a much smaller contact area than boots, concentrating the force and creating higher pressure. This increased pressure is more likely to exceed the ice's strength, causing it to break.
9. Why is it important to distinguish between stress and pressure in engineering calculations?
Distinguishing between stress and pressure is crucial in engineering calculations because they represent different physical phenomena. Pressure calculations are used for fluid systems and external forces on surfaces, while stress calculations are essential for understanding internal forces and material behavior. Using the wrong concept could lead to serious design flaws or safety issues.
10. How does hydrostatic pressure differ from stress in solids?
Hydrostatic pressure is the pressure exerted by a fluid at rest, which is equal in all directions. In contrast, stress in solids can vary in direction and magnitude throughout the material, depending on how forces are applied and the material's properties.
11. How does stress relate to strain in materials?
Stress and strain are closely related concepts in material science. Stress causes strain, which is the deformation of a material in response to applied forces. The relationship between stress and strain is described by Hooke's Law for elastic materials, where stress is proportional to strain up to the elastic limit.
12. What is the difference between normal stress and shear stress?
Normal stress acts perpendicular to a surface, either pulling the material apart (tensile stress) or pushing it together (compressive stress). Shear stress, in contrast, acts parallel to a surface, tending to cause layers within the material to slide past each other.
13. How does the concept of stress help in understanding material fatigue?
Stress plays a key role in material fatigue, which is the weakening of a material due to repeated loading and unloading. By understanding the stress levels and cycles a material experiences, engineers can predict when fatigue failure might occur and design components to withstand long-term use without failing unexpectedly.
14. How does stress distribution change in a material with non-uniform cross-section?
In materials with non-uniform cross-sections, stress is not evenly distributed. Areas with smaller cross-sections experience higher stress for a given force, as stress is inversely proportional to area. This principle is crucial in designing structures, as these areas of higher stress concentration can be potential weak points.
15. Why is the concept of stress important in understanding the behavior of materials at the atomic level?
At the atomic level, stress affects the bonds between atoms in a material. Understanding stress helps explain phenomena like plastic deformation, where atoms shift their positions permanently, and elastic deformation, where atoms temporarily move but return to their original positions when the stress is removed. This atomic-level understanding is crucial for developing new materials with specific properties.
16. What is the fundamental difference between stress and pressure?
Stress is an internal force exerted by one part of a body on another, measured in units of force per unit area (e.g., N/m²). Pressure, on the other hand, is the force applied perpendicular to a surface per unit area, typically from an external source. While both are measured in the same units, stress occurs within a material, while pressure is applied to a surface.
17. Can a material experience stress without external pressure being applied?
Yes, a material can experience stress without external pressure. Internal stresses can arise from various factors such as temperature changes, manufacturing processes, or the material's own weight. For example, a bent metal bar experiences internal stress even without external pressure being applied.
18. How does the direction of force application differ between stress and pressure?
Pressure is always applied perpendicular to a surface, while stress can act in various directions within a material. Stress can be compressive, tensile, or shear, depending on how the forces are applied and how the material responds.
19. Why is the concept of stress important in engineering and material science?
Stress is crucial in engineering and material science because it helps predict how materials will behave under different loads. Understanding stress allows engineers to design structures and components that can withstand expected forces without failing, ensuring safety and efficiency in various applications.
20. How does the area over which a force is applied affect stress and pressure?
Both stress and pressure are inversely proportional to the area over which the force is applied. As the area increases, stress and pressure decrease for a given force. This relationship is expressed in the formula: Stress or Pressure = Force / Area.
21. Why is it important to consider both stress and strain when analyzing material behavior?
Considering both stress and strain is essential because they provide complementary information about a material's behavior. Stress indicates the internal forces experienced by the material, while strain shows how much the material deforms in response to these forces. Together, they give a complete picture of a material's elastic and plastic behavior, crucial for predicting performance and failure points.
22. How does the principle of stress transfer apply in composite materials?
In composite materials, stress transfer occurs between different components, typically a strong, stiff reinforcement (like fibers) and a softer matrix material. The matrix transfers stress to the reinforcement, allowing the composite to bear higher loads than either component could alone. Understanding this stress transfer is crucial for designing effective composite materials for specific applications.
23. Can you explain how stress analysis is used in optimizing the design of aerospace structures?
Stress analysis is fundamental in aerospace design, where structures must be both strong and lightweight. Engineers use advanced computational methods to model how different parts of an aircraft or spacecraft experience stress under various conditions (takeoff, landing, maneuvering). This analysis helps identify areas of high stress, allowing designers to reinforce critical points, redistribute loads, or change materials to ensure structural integrity while minimizing weight.
24. How does the concept of stress shielding apply in biomedical engineering, particularly in implant design?
Stress shielding occurs when an implant (like a hip replacement) takes on a larger share of the load than the surrounding bone. This can lead to bone density loss as the bone is no longer subjected to its normal stress levels. Understanding this phenomenon is crucial in implant design to ensure that the implant and bone share the load appropriately, maintaining bone health and implant longevity.
25. How does the concept of stress relate to the phenomenon of magnetostriction?
Magnetostriction is the change in a material's shape or dimensions in response to a change in its magnetization. This phenomenon demonstrates a direct relationship between magnetic fields and mechanical stress in certain materials. Understanding this interaction is important in designing sensors, actuators, and other devices that convert between magnetic and mechanical energy.
26. How do stress and pressure affect the design of underwater structures?
In underwater structures, both stress and pressure are critical considerations. The hydrostatic pressure of water increases with depth and acts on all surfaces of the structure. This external pressure creates internal stresses within the material of the structure. Engineers must design underwater structures to withstand these pressures without experiencing excessive stress that could lead to failure.
27. How does the principle of stress distribution apply to the design of bridges?
In bridge design, understanding stress distribution is crucial for ensuring structural integrity. Engineers design bridges to distribute stress evenly across the structure, avoiding stress concentrations that could lead to failure. This involves careful consideration of the bridge's shape, materials, and support structures to manage both compressive and tensile stresses under various load conditions.
28. Can you explain why a full water balloon feels firm, relating it to the concepts of stress and pressure?
A full water balloon feels firm due to the interplay of pressure and stress. The water inside exerts pressure equally in all directions on the balloon's surface. This internal pressure creates tension (a form of stress) in the balloon's material. The balloon's elasticity allows it to stretch until the stress in its material balances the internal pressure, resulting in a firm feel.
29. How does the concept of stress relate to the phenomenon of thermal expansion in materials?
Thermal expansion occurs when materials change size due to temperature changes. This expansion (or contraction) can create internal stresses, especially in constrained materials or those with different expansion rates. Understanding these thermal stresses is crucial in engineering, as they can lead to material failure if not properly accounted for in design.
30. How does the concept of stress help in understanding and preventing material failure?
Understanding stress is key to preventing material failure. By analyzing stress distributions and magnitudes in a material or structure, engineers can identify potential weak points or areas prone to failure. This knowledge allows for design modifications, material selection, or reinforcement to ensure that stresses remain below the material's yield or ultimate strength, thus preventing failure.
31. Can you explain the difference between engineering stress and true stress?
Engineering stress is calculated using the original cross-sectional area of a material, while true stress uses the actual, instantaneous area. In most materials, as they deform under load, their cross-sectional area changes. Engineering stress is simpler to calculate and is often used in design, but true stress provides a more accurate representation of the material's state, especially at high strains.
32. Why is the concept of stress important in geophysics and plate tectonics?
In geophysics and plate tectonics, stress plays a crucial role in understanding Earth's dynamics. Tectonic plates experience various stresses due to mantle convection, gravitational forces, and interactions with other plates. These stresses lead to phenomena like earthquakes, mountain formation, and continental drift. Analyzing stress patterns helps geologists predict seismic activity and understand long-term geological processes.
33. How does stress concentration affect the design of mechanical parts?
Stress concentration refers to areas in a material where stress is significantly higher than the average stress in the part. These often occur at sharp corners, holes, or sudden changes in cross-section. In designing mechanical parts, engineers must account for these stress concentrations by either modifying the geometry (e.g., adding fillets or rounds) or reinforcing high-stress areas to prevent premature failure.
34. Can you explain how stress waves propagate through materials during impact?
When an impact occurs, it creates stress waves that propagate through the material at the speed of sound in that medium. These waves can be compressive, tensile, or shear, depending on the nature of the impact. As they travel, they can reflect off boundaries, interfere with each other, and cause localized areas of high stress. Understanding stress wave propagation is crucial in designing impact-resistant structures and materials.
35. How does the concept of residual stress affect material properties and behavior?
Residual stresses are stresses that remain in a material even when no external forces are applied. They can result from manufacturing processes, heat treatment, or plastic deformation. Residual stresses can significantly affect a material's properties, potentially improving fatigue life and stress corrosion resistance if compressive, or leading to unexpected failures if tensile. Understanding and controlling residual stresses is crucial in material processing and product design.
36. Why is the distinction between stress and pressure important in fluid dynamics?
In fluid dynamics, pressure is a scalar quantity representing the force per unit area exerted by a fluid in all directions. Stress, however, is a tensor quantity that can vary in different directions and includes both normal and shear components. This distinction is crucial for accurately modeling fluid behavior, especially in complex flow situations where shear stresses play a significant role.
37. How does the concept of stress relate to the phenomenon of creep in materials?
Creep is the tendency of a solid material to slowly deform permanently under constant stress, typically at elevated temperatures. The rate of creep depends on the applied stress, temperature, and material properties. Understanding the relationship between stress and creep is crucial in designing components for high-temperature applications, as it helps predict long-term deformation and potential failure under sustained loads.
38. Why is it important to consider both static and dynamic stresses in structural engineering?
Static stresses result from constant loads like a building's weight, while dynamic stresses arise from changing loads like wind, earthquakes, or moving vehicles. Considering both is crucial because materials can fail under dynamic loads even if they're safe under static conditions. Dynamic stresses can cause fatigue, resonance, or sudden failures, so structures must be designed to withstand both types of stress for long-term safety and stability.
39. How does the principle of stress distribution apply to the design of pressure vessels?
In pressure vessel design, understanding stress distribution is critical for safety. The internal pressure creates hoop stress (circumferential) and longitudinal stress in the vessel walls. Engineers use this knowledge to determine appropriate wall thickness, material selection, and reinforcement placement. They also consider stress concentrations around openings or joints to ensure the vessel can safely contain the pressure without failure.
40. Can you explain the relationship between stress and crack propagation in materials?
Stress plays a crucial role in crack propagation. When a crack forms, it creates a stress concentration at its tip. If the local stress exceeds the material's strength, the crack grows. This process continues as long as sufficient stress is applied. Understanding this relationship is fundamental to fracture mechanics and is used to predict material failure, design fail-safe structures, and develop materials with improved crack resistance.
41. How does the concept of stress relate to the piezoelectric effect?
The piezoelectric effect is the ability of certain materials to generate an electric charge in response to applied mechanical stress. Conversely, these materials can change shape when an electric field is applied. This direct relationship between stress and electrical properties is utilized in various applications, from sensors and actuators to energy harvesting devices.
42. Why is understanding stress important in the field of biomechanics?
In biomechanics, understanding stress is crucial for analyzing how biological tissues respond to forces. This knowledge is applied in studying joint mechanics, designing prosthetics, and understanding injury mechanisms. For example, stress analysis helps in developing treatments for conditions like osteoporosis by understanding how bone responds to different loading conditions.
43. How does the concept of stress apply to the study of plate tectonics and earthquakes?
In plate tectonics, stress accumulates along plate boundaries as tectonic plates move. When this stress exceeds the strength of the rock, it results in sudden movement, causing earthquakes. Understanding stress distributions in the Earth's crust helps geologists predict earthquake likelihood and understand the forces driving continental drift and mountain formation.
44. Can you explain how stress analysis is used in the design of sports equipment?
Stress analysis is crucial in designing sports equipment for performance and safety. For example, in designing a tennis racket, engineers analyze stress distribution to create a sweet spot that maximizes power and control while minimizing vibrations that could lead to injuries. Similarly, in helmet design, stress analysis helps create structures that effectively dissipate impact forces to protect the wearer.
45. Why is it important to consider both macro-scale and micro-scale stresses in material science?
Considering both macro-scale and micro-scale stresses provides a comprehensive understanding of material behavior. Macro-scale stresses affect the overall shape and integrity of a structure, while micro-scale stresses influence phenomena like crack initiation, dislocation movement, and grain boundary interactions. Understanding both scales is crucial for predicting material performance, designing microstructures, and developing advanced materials with specific properties.
46. How does the concept of stress apply to the study of phase transformations in materials?
Stress plays a significant role in phase transformations, which are changes in the crystal structure of a material. Applied stress can alter the thermodynamics and kinetics of these transformations, affecting the temperature at which they occur and the resulting microstructure. This understanding is crucial in processes like heat treatment of metals, where controlled stress can be used to achieve desired material properties.
47. Can you explain how stress analysis is used in the field of dentistry?
In dentistry, stress analysis is used to design and evaluate dental restorations, implants, and orthodontic appliances. For example, finite element analysis is used to model how forces are distributed in a tooth with a filling or crown, helping to predict potential failure points and optimize designs. This application of stress principles helps create longer-lasting, more comfortable dental solutions.
48. How does the concept of stress relate to the phenomenon of photoacoustic effect?
The photoacoustic effect occurs when a material absorbs light, causing localized heating and thermal expansion. This rapid expansion creates stress waves that propagate through the material as sound. Understanding the stress dynamics in this process is crucial for applications in biomedical imaging, materials characterization, and non-destructive testing.
49. Why is understanding stress important in the field of nanotechnology?
In nanotechnology, stress plays a crucial role due to the high surface-area-to-volume ratio of nanomaterials. Surface stresses can significantly affect the properties and behavior of nanostructures. Understanding these stress effects is essential for designing nanomaterials with specific mechanical, electrical, or chemical

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