Physics · Mechanical Properties Of Solids · NEET
Not exactly. Longitudinal stress is the wider name for any stress acting ALONG the length of a body (force perpendicular to the cross-section area). It has two types: tensile (pulling force, body gets longer) and compressive (pushing force, body gets shorter). So tensile stress is one kind of longitudinal stress, not a separate thing. In NEET most wire problems are tensile because a hanging weight pulls the wire down.
Both use the same formula, stress = F/A, and both act along the length. The only difference is direction. In tensile stress the two forces pull outward, so the length increases (ΔL is positive). In compressive stress the two forces push inward, so the length decreases (ΔL is negative). A stretched rubber band feels tensile stress; a pillar holding a roof feels compressive stress.
For the definition, longitudinal strain = ΔL/L. In compression the length decreases, so ΔL is negative and the strain is negative. But in most NEET numerical answers we report the magnitude (size) of the strain, so you write the positive number and just say 'compressive'. Only add the minus sign when the question asks for the sign or when you compare directions.
They are the same idea. F is the force stretching the wire. If a weight of mass m hangs from the wire, the force is its weight W = mg, so stress = W/A = mg/A. If the question gives a general force F, use F/A. In the 2023 NEET question a weight W hangs from a wire of area A, so the longitudinal stress is simply W/A.
Strain = ΔL/L is a length divided by a length. The metres cancel out, so strain is just a pure number with no unit and no dimension. This is true for tensile and compressive strain both. Stress, on the other hand, has the unit N/m² (pascal, Pa) because it is force divided by area.
A wire is suspended from the ceiling and stretched by a weight W attached at its free end. The longitudinal stress at any point of cross-sectional area A of the wire is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
The SI unit is N/m², also called the pascal (Pa), because stress is force divided by area. Longitudinal strain has no unit because it is a ratio of two lengths.
Longitudinal stress = F/A (force along the length divided by cross-section area). Longitudinal strain = ΔL/L (change in length divided by original length).
Stress is not a simple vector; it is a tensor, because it depends on both the direction of the force and the orientation of the area it acts on. For NEET numericals you treat the magnitude F/A as a number and state whether it is tensile or compressive.
Longitudinal strain is produced by a force acting along the length of the body, perpendicular to its cross-section. A pulling force gives tensile (length increases) and a pushing force gives compressive (length decreases) strain.
Within the elastic limit, Young's modulus Y = longitudinal stress / longitudinal strain = (F/A) / (ΔL/L). So Y measures how strongly a material resists being stretched or compressed along its length.
