The main differentiating point for stress vs pressure is that Pressure is the external force applied on the unit area of the object while Stress is the internal resistive force per unit area developed by an object to resist the deformation.
Stress:
Stress is the intensity of the internal resistive force generated by an object to resist the deformation. It may be generated due to the application of the external force or due to the uneven heating of the object.
Stress is given by,
`\text{Stress}=\frac{\text{Resistive force}}{\text{Area}}`
The SI unit of the stress is Pascal (or N/m²) while the FPS unit is lb/ft².
Example: The stress generated in a rubber band or rope when it is subjected to the tensile force at both ends helps to resist the deformation
Pressure:
The pressure is the intensity of the externally applied force onto the object and it is given by,
`\text{Pressure}=\frac{\text{Force}}{\text{Area}}`
The SI unit of the pressure is Pascal (or N/m²) while the FPS unit is lb/ft².
Pressure is also measured by the use of different gauges used for the pressure measurement. The pressure is only described by the magnitude and therefore the pressure is considered as a scalar quantity.
Example: Pressure created by the compressed air inside of the cylinder, Pressure created by the atmosphere on the earth, etc.
Difference between stress and pressure:
| Sr. No. | Pressure | Stress |
|---|---|---|
| 1] | Pressure is the external force applied to the unit area of the object. | Stress is the internal resistive force per unit area developed by an object to resist the deformation. |
| 2] | It is also called as Intensity of the external force. | It is also called as the intensity of the internal resistive force. |
| 3] | Pressure is applied externally. | Stress is developed internally. |
| 4] | Pressure is normal to the surface. | The stress may be in a perpendicular or parallel direction. |
| 5] | Pressure is a scalar quantity. | Stress is described by using magnitude, direction, and point of application (hence it is also known as a second-order tensor) |
| 6] | Pressure can be directly measured by the use of gauges. | Stress can’t be measured directly by the use of any device. |
| 7] | The magnitude of pressure is the same in all directions. | The magnitude of stress may be same or different in all directions |
| 8] | Pressure is responsible for the deformation of an object. | Stress helps to resist the deformation in an object. |
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