Physics · Mechanical Properties Of Solids · NEET
| What changes | Young's Y: length (long dimension) | Bulk B: volume of whole body |
| Type of stress | Young's Y: tensile / compressive (normal, along length) | Bulk B: pressure (normal, all-round surface) |
| Type of strain | Young's Y: longitudinal strain ΔL/L | Bulk B: volume strain ΔV/V |
| Formula | Young's Y = (F/A)/(ΔL/L) | Bulk B = −p/(ΔV/V) |
| Applies to | Young's Y: solids only | Bulk B: solids, liquids and gases |
| Shear modulus (G) note | Shear G: change in SHAPE, stress F/A tangential, strain Δx/L (=angle θ) | Shear G = (F/A)/(Δx/L); zero for liquids and gases; controls twisting and springs |
Look at what is CHANGING. If length changes (a wire is pulled or a rod is stretched) it is Young's modulus. If the shape changes but volume stays the same (top face slides over the bottom face, or a body is twisted) it is Shear modulus. If the volume changes because pressure acts equally from all sides (a body under water or gas pressure) it is Bulk modulus. One quick test: only Bulk modulus involves pressure acting on the whole surface.
Yes. Shear modulus and modulus of rigidity are two names for the exact same quantity, symbol G (sometimes written η). NCERT uses G. It is the ratio of shearing stress to shearing strain. So if a question says 'modulus of rigidity', treat it as shear modulus.
When you pull the two ends of a coil spring, the spring gets longer, but the wire that makes the coil is not stretched along its length — it is TWISTED. Twisting is a shear deformation, so the stiffness of the spring depends on the shear modulus G of the wire material, not its Young's modulus. NEET 2022 tested exactly this idea.
No. Liquids and gases cannot resist a change in shape, so they have NO shear modulus (G = 0 for an ideal fluid). They also cannot be pulled like a wire, so Young's modulus does not apply. Fluids only resist a change in volume, so they have only a Bulk modulus. Solids have all three.
For most solids there is no single fixed rule, but a common pattern for metals is Y > B > G. Young's modulus and Bulk modulus are usually of similar large size, while the shear modulus is smaller (often roughly one-third of Young's modulus). NEET does not ask you to memorise exact ratios, only to know each modulus and its formula.
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. −VP/ΔV Choose the correct answer.
Statement I: The stretching of a coil spring is determined by the shear modulus of the material of the spring. Statement II: A coil spring of copper has more tensile strength than a steel spring of same dimensions. Choose the most appropriate answer.
The bulk modulus of a spherical object is B. If it is subjected to uniform pressure p, the fractional decrease in radius is
Try the real previous-year questions from this chapter — each with the answer and a full solution.
All three have the same SI unit: pascal (Pa) or N/m². This is because each is a stress divided by a strain, and strain has no units, so every modulus carries the unit of stress.
Shear modulus (G), also called modulus of rigidity. It measures resistance to a change in shape where the volume stays the same, such as one face sliding parallel to the opposite face.
No. Young's modulus is for stretching a solid along its length. Gases and liquids cannot be stretched like a wire, so only bulk modulus applies to them. They have no Young's modulus and no shear modulus.
Compressibility is simply the reciprocal of bulk modulus, k = 1/B. A material with a high bulk modulus is hard to compress, so it has low compressibility. This link appears directly in the NEET 2026 matching question above.
Yes. Every elastic modulus is defined as stress ÷ strain in the region where Hooke's law holds, that is within the proportional/elastic limit where stress and strain are proportional. Beyond that the ratio is no longer constant.
