Question

An ideal fluid has one of the following characteristics

• A. Zero surface tension and incompressible
• B. Zero shear stress and behaves as a perfect gas
• C. Constant density and viscosity
• D. Zero viscosity and incompressible

Hint:

Ideal Fluid = Inviscid ($\mu = 0$) + Incompressible ($\rho = \text{constant}$).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
An ideal (perfect) fluid is a theoretical fluid model having zero internal friction and constant volume under pressure.
Key Formula or Approach:
\[ \mu = 0 \text{ (Inviscid/Non-viscous)}, \quad \rho = \text{constant} \text{ (Incompressible: } \frac{d\rho}{dt} = 0\text{)} \]

Step 2: Detailed Explanation:
In fluid mechanics:
1. Non-viscous (Inviscid): Dynamic viscosity \(\mu = 0\). No shear stresses ($\tau = 0$) exist between fluid layers during motion.
2. Incompressible: Density \(\rho\) remains strictly constant regardless of pressure changes ($K = \infty$).
Real fluids possess both finite viscosity and slight compressibility.

Step 3: Final Answer:
Thus, an ideal fluid has Zero viscosity and is incompressible, matching option (D).