Within the elastic region (see the graph below), there exist a between the force applied and the change in the physical state of object. Experiments have shown that the elastic behavior can be by the following relations with the condition that the change in physical state is small in compared to the original. It can be that the stress is directly proportional to the strain within the line region. This relationship is expressed by Hooke''s Law in two ways.
          1. The equation F = - kx
          2. young''s modulus(Y)=tensile stress/tensile strain
          3. bulk''s modulus(Y)=bulk stress/bulk strain