Question

When a fluid is in streamline flow, the reason of viscous force acting between its two layers is:

• A. transport of energy from one layer to another
• B. transport of linear momentum from one layer to another
• C. same velocity of molecules
• D. the variable density along the length of the tube

Answer 1

The correct option is B transport of linear momentum from one layer to another

Viscosity comes about from collisions between the molecules of the fluid in which some of the momentum of the fast moving molecules is transferred to the slower molecules. This transfer of momentum from fast to slow regions has a "calming" influence on the flow, since it opposes any situation where a fast moving and slow moving region are in close contact. Because of viscosity, each "chunk" of fluid will tend to move at the same velocity as the surrounding "chunks".