Have you ever wondered how different fluids flow? Why honey does not flow as easily as water?
Consider cornstarch and quicksand
What is stress?
It is because of viscosity! Viscosity is the resistance to flow, which relates to an even bigger concept known as momentum transfer.
Oblek is a mixture made out of cornstarch and water. This mixture acts like a solid and resists force.Quicksand, has a structure that becomes more viscous as the applied stress increases.
Stress encompasses the internal force exerted by neighboring particles on each other. The image above, has a knife spreading butter. Shear stress in being applied as the butter moves in parallel to the surface.