The primary difference between stress and pressure is that pressure is the measure of force applied per unit area, whereas stress is the force per unit area experienced by a material.
What is Stress?
Stress arises when an external force is applied to a material, causing it to resist changes in shape or deformation by generating internal forces. For instance, when you stretch a spring, it experiences stress as it strives to return to its initial configuration.
This phenomenon occurs because the material’s atomic structure resists changes in interatomic distances. Therefore, stress is the measure of the internal resistance per unit area within the material in response to an applied force.
What is Pressure?
Pressure, a term commonly employed within fluids, represents the force applied per unit area. This property remains consistent in all directions within the fluid at a specific point. Pressure finds its utility in mechanical applications, particularly in hydraulic machinery where it’s used to apply a specific amount of force.
Pressure is essentially the force exerted by an object on the area it affects. For instance, envision a ball colliding with a wall; it exerts pressure on the wall. This concept falls under the domain of thermodynamics, and pressure is considered a scalar quantity. It establishes a connection between the vector area element (a vector pointing perpendicular to the surface) and the normal force acting upon it.
Pressure serves as an intrinsic property, primarily associated with fluids. It relies on the transfer of momentum among the atoms or molecules confined within the volume of a liquid or gas, occurring on a microscopic scale.
Stress vs Pressure
The key differences between stress and pressure are given below:
| Pressure | Stress |
| Pressure is the external force exerted on the object’s unit area. | Stress is defined as an object’s internal resistive force per unit area created to resist the deformation. |
| It is also known as the external force’s intensity. | It is also known as internal resistive force intensity. |
| External pressure is exerted. | Internally, stress is created. |
| The surface is under normal pressure. | The stress can be applied in either perpendicular or parallel direction. |
| It is a scalar quantity. | The size, direction, and point of application of stress is used to describe it (hence it is also known as a second-order tensor). |
| Gauges can be used to directly measure pressure. | Stress cannot be measured directly by using any equipment. |
| The pressure magnitude is the same in all directions. | The quantity of tension in all directions may be the same or different. |
| The deformation of an object is caused by pressure. | Stress aids in the resistance of an object to deformation. |