Laws of Fluid Friction

The laws of fluid friction are:

1. First law: The fluid friction increases with an increase in the area of contact between the surface and the fluid.
2. Second law: The fluid friction increases with an increase in the velocity gradient of the substance.
3. Third law: The fluid having a higher coefficient of fluid friction or eta (η) has a higher value of fluid frictional force.

The rules hold differently for different lubricants. It is indirectly proportional to the temperature of the lubricants. The formula for the fluid friction can be derived by the following experiment:

In the given experiment it can be shown that the force Ϝ necessary to move the top plate in the figure is directly proportional to the area Α, the difference of speed between the layers ∆ν and inversely proportional to the spacing of the plates ∆y.

That is: Ϝ∽Α and Ϝ∽∆ν and Ϝ∽1∕∆y

This gives the equation:

Ϝ = η Α ∆ν∕∆y

Fluid friction occurs between fluid layers that are moving relative to each other. This internal resistance to flow is called viscosity or viscous drag or fluid friction. In normal terms, the viscosity of a fluid is described as its “thickness” of the fluid. Thus, water is “thin”, having a lower viscosity, while honey is “thick”, having a higher viscosity. The less viscous the fluid, the greater its ease of deformation or movement.

All real fluids (except superfluids) offer some resistance to shearing and therefore are viscous. Although the term “fluid” includes both the liquid and gas phases, in common usage, “fluid” is often used synonymously with “liquid”. Liquids and gases are called fluids because they can be made to flow or move. In any fluid, the molecules themselves are in constant, random motion, colliding with each other and with the walls of any container. In this article, we will learn in detail about fluid friction, its properties, example and more.