exerted by a spring that obeys Hooke's law is proportional to the extension or compression, 
of the spring from its unstretched length, so that 
where 
is the spring constant. [P2.3, P2.4, P5.1, P5.2]
states: that for sufficiently small stress, the strain in a material is directly proportional to the stress causing it. [P7.6]
therefore requires: that the restoring force, exerted by a spring that obeys Hooke's law is proportional to the extension or compression, of the spring from its unstretched length, so that where is the spring constant. [P2.3, P2.4, P5.1, P5.2]
sometimes is expressed: in terms of the applied force 
which is required to maintain a given extension. [P2.3, P2.4, P5.1, P5.2]
leads: to the definition of a range of elastic moduli such as Young's modulus, shear modulus and bulk modulus. [P7.6]
Copyright 1997, The Open University