Energy is stored by the system, then released.
Energy performs work on the material.
In between elastic and viscous behaviour lies the real world of most substances, which are viscoelastic materials. The rheology described on these net-pages is for slurries and emphasises the underlying chemical effects. We continue with some definitions and common terminology used in rheology. For ideal viscous materials, the rate of deformation is in proportion to the force applied. Deformation ceases when the applied force is removed.