Physics · Mechanical Properties Of Solids · NEET
Lateral strain is measured ACROSS the force, at 90 degrees to it. If you pull a wire lengthwise, its diameter changes sideways, and that sideways change (Δd/d) is the lateral strain. Longitudinal strain (ΔL/L) is the one measured ALONG the force direction. Students lose marks by swapping these, so fix it: force direction = longitudinal, perpendicular direction = lateral.
The material has (nearly) fixed volume. When you pull it and it gets longer, the atoms rearrange and the wire compensates by shrinking across its width. So longitudinal strain is positive (length increases) while lateral strain is negative (diameter decreases). This sideways shrinking is exactly the lateral strain.
Longitudinal strain = ΔL / L (change in length over original length, along the force). Lateral strain = Δd / d or ΔD / D (change in width/diameter over original width, across the force). Both are ratios of same-type quantities (length/length), so both are pure numbers with NO units and NO dimensions.
Yes, for stretching. Longitudinal strain is positive (length grows) and lateral strain is negative (diameter shrinks). For compression it flips: length shrinks (negative) and width bulges out (positive). Because of this, Poisson's ratio σ = -(lateral strain)/(longitudinal strain) carries a minus sign so that the final value comes out positive.
It is called Poisson's ratio, written σ (sigma). σ = -(Δd/d)/(ΔL/L) = -(lateral strain)/(longitudinal strain). This exact ratio was asked in NEET 2026. For most solids σ lies between 0 and 0.5. Learn the limits separately on the Poisson's ratio range page.
Match List I with List II. List I: A. Young's Modulus, B. Compressibility, C. Bulk Modulus, D. Poisson's Ratio. List II: I. (Δd/d)/(ΔL/L), II. FL/(A·ΔL), III. -(1/V)(ΔV/P), IV. -V·P/ΔV. Choose the correct answer.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Longitudinal strain is bigger in magnitude. Since Poisson's ratio (lateral over longitudinal) is between 0 and 0.5 for real solids, lateral strain is at most half the longitudinal strain, and usually much less.
Only if Poisson's ratio is zero, which is very rare (like cork). For normal materials, stretching along the length always causes some sideways shrinking, so both strains occur together.
No. It is a change in width divided by original width, so it is a pure number with no unit and no dimension, exactly like longitudinal strain.
No. Lateral strain is the sideways change in size when you pull or push along a length (linked to Poisson's ratio). Shear strain is an angle change when a force acts parallel to a surface (linked to shear modulus). They are different ideas.
