Question

What is fluid friction?

Answer 1

Hint: When two bodies slide over one another, there exists a resistive force between them due to interaction between the molecules of two bodies. In fluids also, this type of force is experienced when there is another body or medium moves through it.

Complete step by step answer:
Friction is a resisting force which comes into action when two bodies slide over each other. In other words, we can say that friction opposes the motion of one body over another.
Underlying working principle of friction is that when two bodies come in contact with each other and try to slide over each other, their surface may not be smooth and may have bumps and uneven surfaces. This leads to jerky motion which is characterized as friction.
Friction can be seen in action everywhere around us and it is experienced in fluids also. When a body moves through a fluid which may be liquid or air, there is interaction between molecules of fluid and the body which tries to resist the motion of the body through that fluid. This is called fluid friction.
In air, this frictional force is experienced by a body moving at a large speed against the air, for example, an airplane experiences this fluid friction when it's flying in the atmosphere. In order to reduce this friction, the body of an airplane has a streamline shape such that it cuts through the air resistance which saves fuel and improves speed of the airplane.
The viscosity of a fluid represents the frictional force between the layers of a fluid. A fluid which has greater friction between its layers resists its flow and has greater viscosity while a liquid which has less viscosity has lower fluid friction.
A swimmer experiences fluid friction while swimming in water due to which the swimmer has to push against the water in order to propel itself.

Note: Fluid friction is much more in liquids compared to gases since the number of molecules interacting with the body moving through liquids is more than that in air. Streamlining is required more in water than in air.