Intro to Viscosity

Viscosity in layman's terms is how thick a fluid is or how hard it is for a fluid to flow. Honey flows really slowly so its viscosity is quite high whereas water flows really easily so it has a low viscosity. Viscosity is due to intermolecular forces and friction between the molecules. When viewing this phenomenon in large scale the viscosity of the fluid acts like friction by changing the kinetic energy into heat energy. According to Fowler, the coeeficient of viscosity n (greek letter...) is "a measure of how much heat is generated when faster fluid is flowing by slower fluid, but it is also a measure of the rate of transfer of momentum from the faster stream to the slower stream." So in general viscosity is different speeds of flow in a fluid.

Viscosity of fluids has applications in aerodynamics because objects moving through air encounter air drag which is essentially the effect of viscosity of the air and also of fluid/solid interaction. viscosity also comes into play in any mechanical device that uses a liquid to lubricate moving parts. The friction is reduced this way because the two solids are not in contact with each other but the viscosity of the fluid has some friction of its own that the device will has to take care of. For a more in depth discussion on this interesting topic of viscosity and the physics behind it i would encourage you to read this article by Michael Fowler.