(2) Fluid friction:
Fluid friction occurs when adjacent layers in a fluid (liquid or gas) are moving at different velocities. This motion causes frictional forces between fluid elements, and these forces depend on the relative velocity between layers. When there is relative velocity between layers, there is no fluid friction. Fluid friction depends on the velocity gradients within the fluid and on the viscocity of the fluid.
(3) Internal friction:
Internal friction occurs in all solid materials subjected to cycle loading.
Friction |
Types of friction: (1) Dry friction: Dry friction occurs when the unlubricated (rough) surfaces of two solids are in contact under a condition of sliding or a tendency to slide. A friction force tangential to the surfaces of contact occurs both during the interval leading up to impending slippage and while slippage takes place. The direction of this friction force always opposes the motion or impending motion.This type of friction is also called Coulomb friction. |