The friction which exist between two layers of liquid in relative motion is called.

Analysis

The question asks for the specific term used to describe the internal resistance or "friction" that occurs when different layers of a liquid move past each other at different velocities.

Concept Explanation

In physics, fluids (liquids and gases) possess a property that resists the relative motion of their layers. This is essentially the fluid's version of friction.

• Viscosity is defined as the internal friction of a fluid. When a liquid flows, the layer in contact with a surface moves slower than the layers further away. The force required to maintain this velocity gradient is due to the viscosity of the fluid.
• Capillarity refers to the ability of a liquid to flow in narrow spaces without the assistance of external forces (like gravity).
• Surface Tension is the property of a liquid surface that allows it to resist an external force, caused by the attraction of particles in the surface layer.
• Cohesion is the intermolecular force that holds molecules of the same substance together.

Step-by-Step Solution

1. Identify the phenomenon: The question describes "friction between two layers of liquid in relative motion."
2. Evaluate the options: • A (Capillary) relates to flow in narrow tubes. • B (Surface) is too broad and usually refers to surface tension. • C (Viscosity) is specifically defined as the measure of a fluid's resistance to gradual deformation by shear stress or tensile stress (internal friction). • D (Cohesion) is the force of attraction between molecules, not the friction between moving layers.
3. Conclusion: Viscosity is the correct physical term for the internal friction of a fluid.

Correct Answer

The correct option is C.

Exam Tip

Think of viscosity as the "thickness" or "stickiness" of a liquid. Honey has high viscosity (it flows slowly because the layers have high internal friction), while water has low viscosity. Remembering this relationship will help you identify the concept easily in future exams!