what is hooke's law? does it apply to elastic materials or to inelastic materials?
Hooke's law. When studying springs and elasticity, the 17ᵗʰ century physicist Robert Hooke noticed that the stress vs strain curve for many materials has a linear region. Within certain limits, the force required to stretch an elastic object such as a metal spring is directly proportional to the extension of the spring.
Slide 2 of 14. Notes: The fact that strain means relative change in shape or size implies that it is dimensionless and has no units. Stress, on the other hand, has dimension of force per unit area, or, less often, force per unit length. This statement of Hookes Law (stress proportional to strain) is a more general statement than the more specific one given in a later slide, that restoring force is proportional to displacement.