Physics gives us reasons behind everything that occurs in our daily life. It contains mathematical as well as theoretical laws. It is a subject that analyses surroundings and their actions through time and space.

In this, people learn about different forces, stress and strain applied in an object, whether moving or static. And the changes or the deformation it goes through at every stage.

Stress and Strain both are terms of physics where Stress is a force, and Strain is a resulting change or the change which results in an object after applying Stress.

The amount of Strain in an object cannot be measured. It can only be seen and observed through the movement, shape, and form of an object or physical body after the effect of Stress force.

**Stress vs Strain**

The difference between Stress and Strain is that Stress can be measured and has its unit of measurement. Also, when Stress is applied to an object, it produces Strain; therefore, Stress can occur without Strain. While Strain cannot occur independently, there must be the action of Stress force. And Strain cannot be measured, so it does not have any measurement unit.

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Stress is a force that an object goes through when it is subjected to external loading. Then elements from the object will try to oppose the force which is internal resistance generated by elements from the body.

It is a physical quantity which means that it can be measured and recorded. The Greek symbol sigma is used to designate this force. Stress may also exist when no external force is applied to a body.

The Strain occurs after Stress is applied to a body or an object. Without the application of Stress force, there will be no Strain. It can be observed and seen but cannot be measured. Therefore it does not have any measuring unit.

The epsilon symbol is used to denote Strain. The formula says that Strain due to Stress equals the multiplication of change in length and original length of the material.

**Comparison Table**

Parameters of Comparison | Stress | Strain |
---|---|---|

Definition | Stress is a force and is defined as the repelling force to a unit area of the object or deforming and restoring force per unit area. | The Strain is the variation in the shape of an object per the original shape or the deformation per unit area. |

Unit of measurement | Stress has two main categories one is tensile, and another is compressive stress. The measuring unit of Stress is N/m2 (SI). | There are two main types of Strain normal strain and shear strain. It has no unit of measurement. |

Dependence | Stress does not depend on Strain, as it can exist without Strain. | Strain only happens when there is stress or when Stress is applied to an object. |

Types | The various sorts of Stress are tensile, compressive, and shear stress. | Strain is categorized into tensile, compressive, shear, and volumetric strain. |

Symbol and Formula | The Greek symbol sigma designates stress, and the formula for Stress is represented by Stress =force/ Cross-sectional area or σ= F/A. | Strain is symbolized by ‘ε,’ that is epsilon, and the formula is given by: ε= dt/t. |

**What is Stress?**

Stress is defined as a force that can be calculated by dividing the applied force from the cross-sectional area of the object or a body to which the force is applied.

Stress can happen without applying any force because of the internal particles’ collisions. There is a breaking point of Stress force that takes place when the Stress is at its peak or maximum point which is called breaking Stress.

There are so many forms of Stress normal stress, tangential stress, hydraulic stress, radial stress, volume stress or bulk stress, tensile stress, compression stress, etc.

Where normal stress and tangential stress depend on the angle of direction of the applied force, while the hydraulic force takes place in liquids, that is, when an external force is applied to a liquid.

The Système International unit of Stress is newton per meter square. It can also be considered as tension which causes the body to change its shape or dimensions.

And the resulting change in dimension and shape that an object goes through is called Strain.

**What is Strain?**

Strain is described as the amount of change and distortion that an object faces or goes through when Stress is applied to the object.

Strain can only be observed or noticed as it cannot be recorded or calculated; therefore, it has no measuring unit. It is mainly an internal force that an object goes through.

The Strain takes place because of Stress. There is no Strain without the application of Stress in a body.

Strain can be a longitudinal strain, shearing strain, and volumetric strain. Strain only describes the amount of distortion associated with a relative displacement of the object in which these forces act.

The formula for calculating Strain is defined as the change in dimension of an object divided by the original dimension of an object recorded before the application of force.

Elastic modulus also affects the Strain effect on an object.

For example, when Stress is applied to rubber and when the same Stress is applied to a steel wire, the rubber will be changed more in dimensions or shape as compared to steel wire because the elastic modulus of rubber is less than steel.

**Main Differences Between Stress and Strain**

- Stress is a force and is defined as the repelling force to a unit area of the object or deforming and restoring force per unit area. On the other hand, the Strain is the change in shape per the original shape or the deformation per unit area.
- Strain is categorized into tensile, compressive, shear, and volumetric strain. And the various sorts of Stress are tensile, compressive, and shear stress.
- Strain only happens when there is stress or when Stress is applied to an object. In contrast, Stress does not depend on Strain as it can exist without Strain.
- Stress has main categories as tensile and compressive. The measuring unit of Stress is N/m2 (SI) or lb/in2 (USA). In contrast, there are two main types of Strain normal strain and shear strain. It has no unit of measurement.
- Strain is symbolized by ‘ε’, which is epsilon, and the formula is given by: ε= dt/t. While the Greek symbol sigma designates Stress, the formula for Stress is represented by Stress =force/ Cross-sectional area or σ= F/A.

**References**

- https://journals.aps.org/prb/abstract/10.1103/PhysRevB.32.3780
- https://books.google.com/books?hl=en&lr=&id=2fSMOVoAXgYC&oi=fnd&pg=PA295&dq=strain&ots=aFinjIv-xD&sig=AoFhbOSvialUL-0BVdLdHItC_4g

Piyush Yadav has spent the past 25 years working as a physicist in the local community. He is a physicist passionate about making science more accessible to our readers. He holds a BSc in Natural Sciences and Post Graduate Diploma in Environmental Science. You can read more about him on his bio page.