Introduction to Fluid Mechanics

Which of the following is TRUE about a Newtonian fluid?

• Its viscosity depends on the shear rate.

• Its viscosity remains constant regardless of applied shear stress.

• It exhibits both solid and liquid characteristics.

• Its viscosity increases with an increase in temperature.

Answer explanation

Newtonian fluids (like water and air) have a constant viscosity that does not change with applied shear stress, unlike non-Newtonian fluids like blood or ketchup.

In fluid statics, what is the correct relationship between pressure and depth in an incompressible fluid?

• Pressure decreases with depth.

• Pressure remains constant throughout.

• Pressure increases linearly with depth.

• Pressure is independent of depth.

Answer explanation

In an incompressible fluid, pressure increases with depth according to P = ρgh, where ρ is density, g is gravity, and h is depth.

Which principle best explains the lift force acting on an airplane wing?

• Pascal’s Law

• Bernoulli’s Principle

• Archimedes’ Principle

• Poiseuille’s Law

Answer explanation

Bernoulli’s Principle states that faster airflow over the top of the wing creates lower pressure, generating lift.

What property determines a fluid’s resistance to deformation under shear stress?

• Density

• Surface tension

• Viscosity

• Compressibility

Answer explanation

Viscosity is a measure of a fluid’s resistance to shear stress and internal friction.

Which of the following factors primarily distinguishes liquids from gases?

• Liquids are highly compressible, while gases are not.

• Liquids form a free surface under gravity, while gases do not.

• Liquids have no definite volume, whereas gases do.

• Liquids expand to fill any container, while gases do not.

Answer explanation

Liquids maintain a fixed volume and take the shape of their container, forming a free surface when not completely enclosed. Gases, however, expand to fill their container and do not form a free surface.

Which statement about surface tension is INCORRECT?

• It results from cohesive forces between liquid molecules.

• It increases with temperature.

• It allows insects to walk on water.

• t affects the shape of liquid droplets.

Answer explanation

Surface tension decreases as temperature increases because molecular cohesive forces weaken.

Which equation is derived from the principle of conservation of mass in fluid flow?

• Navier-Stokes equation

• Continuity equation

• Euler’s equation

• Bernoulli’s equation

Answer explanation

The Continuity Equation (A₁V₁ = A₂V₂) states that mass flow rate remains constant in an incompressible fluid.

Which force is negligible in inviscid flow analysis?

• Pressure force

• Gravity force

• Viscous force

• Inertial force

Answer explanation

Inviscid flow assumes zero viscosity, simplifying calculations by ignoring frictional forces.

Which condition makes a fluid incompressible?

• Constant velocity

• Constant density

• Constant pressure

• Constant temperature

Answer explanation

Incompressible fluids have negligible density changes under varying pressure conditions (e.g., most liquids).

Which phenomenon occurs when a fluid detaches from a surface due to adverse pressure gradients?

• Flow separation

• Cavitation

• Surface tension

• Turbulence

Answer explanation

Flow separation occurs when a fluid moves past an object, leading to turbulent wake regions and increased drag.