Let’s start with a question.

“What is modulus of elasticity?” . The first and general answer by students would be

“It is stress divided by strain”

Does this answer make sense to a 5th grader?

We often fail to comprehend scientific terms in a qualitative manner. What might actually be the significance of modulus of elasticity? You might know and ‘feel’ stress and strain. But many people don’t know and ‘feel’ modulus of elasticity. What exactly means when we say modulus of elasticity of steel is 200 GPA?

*Modulus of elasticity is also called Young’s modulus or Elastic modulus.*

We all know the famous stress strain graph where we can find yield stress and ultimate tensile stress of a material.

In the graph, there is this linear stress region where Hooke’s law makes sense. It is also the region where the material when deformed tends to revert back to original. Think of a rubber, when it is stretched(and then released) it returns back to its original state.

Again think of a glass, Is it ‘rubbery’? Glass does not show the ‘rubbery’ property on application of nominal stress. It is what we call ‘stiff’. Stiffness is often confused with strength. So you can think of above mentioned examples to differentiate between stiffness and strength.

That is where modulus of elasticity comes into account. Modulus of elasticity qualitatively defines whether the material is ‘rubber’y or ‘glassy’.

The more the value of modulus of elasticity of a material, the more stiff the material is. The more the modulus of elasticity is, the more easier it is to induce temporary deflection in a material.

Sorry to point out that your explanations are misleading. Nobody defines modulus of elasticity as stress by strain. Recovery is central to the concept. It is indeed stress over strain wrt the idealised linear portion of stress strain curve.

The concepts of stiffness and strength are from applied engineering practice and refer to absorption of energy and failure of material under load, and are not central to theory of elasticity.

The stiffness of glass is entirely due to internal structure of the material, and the shape; a fibre of glass is not brittle, and is highly elastic. It is also strong when used properly. There seems to be some confusion between ‘stiffness’, ‘rigidity’ and ‘brittleness’. It is very dangerous to use rubber when explaining elastic behaviour – rubber is not elastic; it is plastic and is not a rigid body.

The problem is that the language used has to be rigid, and indicate limits of application at the out set. You attempt is good, but definitions have to be rigid. It is better to be clinical in word usage and avoid use of non techl. terms, and avoid curtailing definitions.

Noted! Thank you for your comment.