Stress and Pressure

Stress and Pressure are commonly mistaken because of their close nature to each other. Stress is defined as the force per unit area of a material, whereas Pressure is defined as the force exerted per unit area. Let us look at more distinguishing features and differences between the two. Before that, let us study stress and pressure separately to get a clear idea of their concepts.

Stress

The force acting on a material’s unit area is defined as Stress in physics. The impact of stress on the body is referred to as a strain. As a result of Stress, the body may deform. The amount of force experienced by a material is measured in stress units. Stress is classified into three types based on the direction of the deforming forces that act on the body. Let’s go through them one by one. Stress is denoted by the symbol ‘𝞼’

 [𝞼] = F/A.

In simple words, the restoring force per unit area is referred to as Stress. When we apply an external force to the body to change its shape, it develops a restoring force in the opposite direction.

The stress unit has no dimensions. Because it is the ratio of the length shift to the initial length, it is unitless.

There are various types of Stress:

• Normal Stress

Normal stress is applied perpendicular to the body. When the length of the wire or the volume of the body changes, the stress level will be normal.

• Longitudinal Stress

 Longitudinal Stress occurs when the body’s length changes due to normal Stress.

• Bulk Stress

It occurs when normal Stress acts from all directions on a body, causing a change in the volume of the body affected.

• Tensile Stress

It is a type of Stress that causes a body’s length to increase.

For example, pulling on two ends of a rod to lengthen it. Compressive Stress is a type of Stress that shortens a person’s body. Pushing on the two ends of a rod, for example, makes it shorter.

Pressure

Pressure is the force exerted perpendicular to the unit area. This is measured in Pascal. A unit pressure is defined as when one newton of force is exerted per unit area in a one-meter square area

Pressure =Force/Area

This is a scalar quantity with no specific directions. 

When we quote that the direction of pressure changes, we are denoting the direction of force rather than the pressure, as pressure does not have a direction. Force is a vector quantity 

A meteorologist who measures atmospheric pressure around uses the unit hectopascal while divers who dive against the high-pressure zone of ocean use decibar as their unit. Normal standard air pressure is the pressure of air in the normal weather above mean sea level; this is one-atmosphere pressure equals 101.325 Pascals. This is measured using a manometer or barometer where the pressure can be measured using the level of fluid such as mercury and water. Mercury is used mostly

When an object of rho density exerted a certain amount of pressure in the fluid such as water when placed above a height of h, pressure can still be measured as,

Pressure = Density * height(h) *gravitational acceleration (g)

             P=ŕ(rho)GH

We use this measuring of pressure in measuring blood pressure of individuals and lung gaseous pressure to see the functioning of the body. Increased pressure in the body is called high pressure or hypertension. When you have high force you get high pressure as force is proportional to pressure, when we use large area pressure is reduced, as pressure is inversely proportional to area.

This is used as the principle in many industrial types of equipment such as hydraulic suction force equipment, hydraulic brakes, blood pressure, etc. Fluid pressure occurs in two forms one as an open flow source and another as a closed-circuit this helps in estimating the amount of pressure exerted by the molecules over a container.

Difference between Stress and Pressure

Conclusion

Stress and Pressure both have a similar definition but closely observed they both differ in many properties. The important distinguishing property is, that stress is internal and pressure is external. In this article, we looked at stress, pressure, and its differences.