Here's why:
* Viscoelastic materials exhibit properties of both viscous fluids and elastic solids.
* Viscosity refers to a material's resistance to flow (think of honey vs. water).
* Elasticity refers to a material's ability to return to its original shape after deformation.
When you heat rubber or glass, the molecules within them gain more energy and move more freely. This causes the material to become less resistant to deformation (less viscous) and more easily stretched or molded (more elastic).
Other examples of viscoelastic materials:
* Plastics
* Polymers
* Some metals (at high temperatures)
Note: While rubber and glass soften with heat, they do not melt like a typical solid. They undergo a gradual transition from a more solid-like state to a more liquid-like state.
