Question

The unit of stress is:
A. $kg\,{m^{ - 2}}$
B. $N\,k{g^{ - 1}}$
C. $N\,{m^{ - 2}}$
D. $N$

Answer 1

Hint: Here, to find the unit of stress we will first define stress which is stress is the ratio of force acting on the material and area of the material. The unit of stress can be calculated by dividing the units of force and area. The stress on the body results in the deformation of the body.

Complete step by step answer:
Stress is defined as the physical quantity that is used to express the internal forces that the neighboring particle of a material exerts on each other. The stress is denoted by the Greek letter sigma ($\sigma $ ). Also, the stress can be defined as the force per unit area of a material and is given by
$\sigma = \dfrac{F}{A}$
Here, $F$ is the force acting on the material and $A$ is the area of the material.

Now, the force is defined as the push or pull that acts on an object as a result of which the velocity of an object changes. The unit of force is $newton\,(N)$ . Also, the unit of the area is ${m^2}$ . Therefore, the unit of stress can be calculated as
$\sigma = \dfrac{N}{{{m^2}}}$
Therefore, the unit of stress is $N\,{m^{ - 2}}$ .

Hence, option C is the correct option.

Additional information:
There are mainly three types of stress that are discussed below:
NORMAL STRESS:
The normal stress is defined as the force that is applied perpendicular to the cross-sectional area of the body. Normal stress can also be categorized into two types that are longitudinal stress and volumetric stress.
TANGENTIAL STRESS:
The tangential stress is defined as the force that is applied parallel to the cross-sectional area of the body. The tangential force results in the change of the shape of the body.
HYDRAULIC STRESS:
The hydraulic stress is defined as the internal force that is applied per unit area on the liquids. Also, a hydraulic force is defined as the restoring force per unit area that is applied by the liquid on the body.

Note:Students may get confused between the stress and the pressure. Remember, stress is the internal force that is applied to the object. On the other hand, the pressure is the external force that is applied to the object. But, the dimensions and units of stress and pressure are the same.