Stress

To help visualize Stress, think of pressure (force per unit area) which is acting on a cross-section of an object.

Tensile stress:

$$
\sigma = \frac{\text{Force}}{\text{Area of cross-section}}
$$

Area = π r² in case of round bar or rod. For any other shape, apply the area as per the geometry.

Please note carefully that the strong metallic rope is pulling in the same direction as the elongation, it means the Force is acting in the direction of displacement of the material’s molecules that moved apart from each other (hence the bar became longer). Doesn’t this remind you of the term “Work done”? We’ll come back to Work Done in a subsequent topic.