The document discusses the physical states of materials and their behavior under applied forces. It describes three basic material properties - elasticity, plasticity, and viscosity. Materials can exhibit elastic, plastic, viscous or viscoelastic behavior depending on the stress and strain applied over time. Viscoelastic materials have aspects of both elastic solids and viscous fluids. The document also discusses nonlinear, time-dependent and non-Newtonian behaviors exhibited by some materials.