Ans:
1. A substance in the liquid or gas phase is referred to as a fluid.
2. A solid resists the applied shear stress by deforming whereas a fluid deforms continuously under influence of shear stress, no matter how small.
3. In solids shear stress is proportional to strain, but in fluids stress is proportional to shear strain rate (du/dy).
4. Liquid takes the shape of the container it is in and forms a free surface.
5. Gases expand until they encounter the walls of containers and fills entire available space.