OAR Mechanical Comprehension: Fluids Flashcards

Which of the following is an example of a non-Newtonian fluid?

Answer: Ketchup

Ketchup is a shear-thinning non-Newtonian fluid — its viscosity decreases under stress (like shaking the bottle).

A pipe carrying water branches into two equal pipes. If the flow rate in the main pipe is 8 gal/min, what is the flow rate in each branch?

Answer: 4 gal/min

Conservation of mass requires the total flow to be preserved: 8 gal/min splits equally into 4 gal/min per branch.

What is cavitation in a fluid system?

Answer: Buildup of air bubbles at the pump inlet that collapse when pressure rises, causing damage

Cavitation occurs when local pressure drops below vapor pressure, forming bubbles that collapse violently and erode surfaces.

A hydraulic system transmits 2,000 lbs of force through fluid. If there are no losses, the work done by the input piston equals the work done by the output piston because:

Answer: Energy is conserved — force × distance is equal on both sides

Pascal's Law multiplies force but not energy; the output piston moves a shorter distance proportionally, preserving work (W = F × d).

Which condition must be true for Bernoulli's equation to apply without correction?

Answer: The flow must be steady and the fluid ideal (inviscid, incompressible)

Bernoulli's equation in its basic form assumes steady, incompressible, inviscid (frictionless) flow along a streamline.

A fluid exerts a force on a curved pipe bend. In which direction is the net resultant force on the bend if flow turns 90°?

Answer: Diagonally, combining both the inlet and outlet momentum directions

Momentum changes in both the x and y directions at a 90° bend, so the resultant reaction force acts diagonally.

Atmospheric pressure at sea level is approximately 14.7 psi. What is the absolute pressure at the bottom of a pool that creates 5 psi of gauge pressure?

Answer: 19.7 psi

Absolute pressure = atmospheric pressure + gauge pressure = 14.7 + 5 = 19.7 psi.