Which of the following statement about viscosity is not true? it

Analyze the question: We need the statement about viscosity that is NOT true.

Concept: Viscosity is the internal friction in a fluid (liquid or gas) that opposes relative motion between adjacent layers. Newton's law of viscosity gives:

F = ηA(dv/dx)

where

• F = tangential (viscous) force between the layers
• η = coefficient of viscosity
• A = area of the layers in contact
• dv/dx = velocity gradient (change in relative velocity between layers over their separation)

Check each option:

• A. Depends on areas of the surfaces in contact: True. From F = ηA(dv/dx), the viscous force is proportional to the area A.
• B. Occurs in fluids: True. Viscosity is a property of liquids and gases.
• C. Is independent of the relative velocity of the layers: Not true. The viscous force is directly proportional to the velocity gradient, so it depends on the relative velocity of the layers. (Only the coefficient η is independent of velocity for Newtonian fluids, but the viscous force itself is not.)
• D. Depends on the tangential force between the layers: True. The viscous force is tangential to the layers, and it is what F represents in the formula.

Tip: In "which is NOT true" questions, test each option against the formula. Here F = ηA(dv/dx) contains area, force, and velocity gradient, so any statement denying one of these dependencies is the likely false one.