Figure 5. Schematic representation of the relationship between stress and strain during a sinusoidal oscillating strain (, angular velocity) for a perfectly elastic solid (A, Hookean body), a viscoelastic material (B), and a perfectly viscous liquid (C, Newtonian body). In a viscoelastic material, the phase difference between stress and strain is somewhere between (/2 > > 0), and the complex modulus E* is resolved into two components, i.e., the storage modulus E' and the loss modulus E'', shown vectorially. Furthermore, the tangent of the phase angle () between stress and strain is a measure of the ratio of energy loss to energy stored during a cyclic deformation.