Fluid mechanics – Euler’s equation of motion (assumptions) Euler’s equation for inviscid flow is derived under several idealizing assumptions. Which of the following correctly list those assumptions used for the motion of liquids?

Introduction / Context:
Euler’s equation is a cornerstone of ideal fluid mechanics. It expresses Newton’s second law for a fluid particle when viscosity is neglected. Understanding the underlying assumptions is essential because they define when Euler’s equation (and its integrated form, the Bernoulli equation) can be applied reliably in engineering problems.

Given Data / Assumptions:

• Ideal fluid model: inviscid, homogeneous, frequently treated as incompressible for liquids.
• Flow field that is steady for the common derivation used in hydraulics.
• Equation written along a streamline for general three-dimensional flows.
• Cross-sectional uniformity is often invoked when reducing to 1-D forms.

Concept / Approach:
Euler’s differential momentum equation comes from applying Newton’s second law to a fluid element while neglecting viscous stresses. In typical liquid-flow applications, incompressibility and steadiness simplify terms. When engineers move to a 1-D treatment, they additionally assume sectionally uniform velocity to relate pointwise variables to section-averaged values.

Step-by-Step Solution:

Verification / Alternative check:
If viscosity were significant (e.g., near walls, in laminar layers), Navier–Stokes terms with viscous stresses would be required. Euler’s equation is then insufficient, confirming the necessity of the inviscid assumption.

Why Other Options Are Wrong:

• Options A, B, and C are each individually true within the standard derivations; the comprehensive choice is “All of the above”.
• “None of the above” contradicts classical fluid mechanics.

Common Pitfalls:
Blindly applying Bernoulli/Euler to real, highly viscous, or unsteady flows without checking assumptions such as inviscid behavior, steadiness, and streamline alignment.

Final Answer:
All of the above