Question

An incompressible fluid is one in which:

• A. Density changes with pressure
• B. Density remains constant with pressure
• C. Volume increases with temperature only
• D. Viscosity is zero

Hint:

Logic Tip: Break down the word: "In-compressible" literally means "cannot be compressed." If it cannot be compressed, its volume cannot shrink. If its volume doesn't shrink, its density cannot change.

Answer 1

The Correct Option is B

Concept:
In fluid mechanics, compressibility relates to how much a fluid's volume (and subsequently its density) changes when subjected to external pressure forces.

Step 1: Density ($\rho$) is the mass ($m$) of a fluid divided by its volume ($V$). ($\rho = m/V$).

Step 2: Gases are highly compressible. When you apply pressure to a gas, you force the molecules closer together. This decreases the volume while mass stays the same, causing the density to increase.

Step 3: An idealized incompressible fluid is a theoretical concept (often used to model liquids like water) where the molecules are already packed closely together.

Step 4: Because the molecules cannot be squeezed any closer, applying external pressure does not reduce the fluid's volume.

Step 5: If applying pressure causes zero change in volume, and the mass is constant, then the density ($\rho = m/V$) must remain absolutely constant regardless of pressure changes.