Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other.
There are several types of friction:
- Dry friction resists relative lateral motion of two solid surfaces in contact.
- Fluid friction describes the friction between layers of a viscous fluid that are moving relative to each other.
- Lubricated friction is a case of fluid friction where a lubricant fluid separates two solid surfaces.
- Skin friction is a component of drag, the force resisting the motion of a fluid across the surface of a body.
- Internal friction is the force resisting motion between the elements making up a solid material while it undergoes deformation.
What is fluid friction?
Fluid friction occurs between fluid layers that are moving relative to each other. This internal resistance to flow is named viscosity. In everyday terms, the viscosity of a fluid is described as its “thickness”.
All real fluids offer some resistance to shearing and therefore are viscous. It is helpful to use the concept of an inviscid fluid or an ideal fluid which offers no resistance to shearing and so is not viscous.
Examples of Fluid Friction
- If there is a wet surface between two thin glass plates, you will notice that platest get stucked and the bottom plate doesn’t fall when you hold only the top one.
- When any object is dropped in a fluid, the extent of splash is depended on the fluid friction of that particular fluid.
- You find lighter dust particles move fast on the surface of a flowing river. This is due to the high velocity gradient at the top layer of water due to lower dynamic fluid friction at that layer.