Hydraulics and Fluid Dynamics Flashcards

A hydraulic lift uses two pistons. Piston A has a surface area of 2 square inches, and Piston B has a surface area of 10 square inches. If a force of 50 pounds is applied to Piston A, what is the maximum lifting force that can be generated by Piston B?

Answer: 250 pounds

This question applies Pascal's Law, which states that pressure applied to an enclosed fluid is transmitted undiminished to every portion of the fluid and the walls of the containing vessel. The pressure (P) is Force (F) divided by Area (A), so P = F/A. The pressure on Piston A is 50 lbs / 2 in² = 25 psi. This pressure is transmitted to Piston B. The force on Piston B is P × Area B = 25 psi × 10 in² = 250 pounds.

In a horizontal pipe, water flows from a wider section into a narrower section. According to Bernoulli's principle, what happens to the water's speed and pressure as it enters the narrower section?

Answer: Speed increases, pressure decreases

Bernoulli's principle states that for a fluid in motion, an increase in speed occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy. In a horizontal pipe, when the cross-sectional area decreases, the fluid must speed up to maintain the same volume flow rate (the principle of continuity). As the speed increases, the internal pressure of the fluid decreases.

Which of the following properties of a fluid is a measure of its internal resistance to flow?

Answer: Viscosity

Viscosity is the measure of a fluid's internal friction or resistance to flow. A fluid with high viscosity, like honey, flows slowly, while a fluid with low viscosity, like water, flows easily. Density is mass per unit volume, buoyancy is the upward force exerted by a fluid, and compressibility is the ability to be squeezed into a smaller volume.

A scuba diver is 10 meters below the surface of the ocean. A second diver is 20 meters below the surface. How does the pressure on the second diver compare to the pressure on the first diver?

Answer: It is significantly greater.

The pressure exerted by a fluid increases directly and linearly with depth. This is because the pressure is caused by the weight of the fluid column above the point of measurement. Since the second diver is at twice the depth of the first diver, they will experience significantly greater pressure from the weight of the water above them.

A hydraulic system is designed to be 'fail-safe', meaning a small leak should not cause an immediate and catastrophic failure. Which type of fluid would be MOST suitable for this system?

Answer: A nearly incompressible liquid (like oil)

Hydraulic systems rely on Pascal's principle, which works because liquids are nearly incompressible. Using a nearly incompressible fluid like oil ensures that when force is applied to one piston, the pressure is transmitted efficiently to the other. A gas would compress under pressure, storing energy instead of transmitting force, and a small leak would cause a rapid loss of pressure and system failure. Viscosity and density are less critical to the fundamental operation than incompressibility.

In the context of fluid dynamics, which of the following describes a smooth, orderly flow where fluid particles move in parallel layers without mixing?

Answer: Laminar flow

Laminar flow is characterized by fluid particles moving in smooth, parallel layers or paths (streamlines) with little to no mixing between them. Turbulent flow, in contrast, is chaotic and characterized by eddies and swirls. While the flow may be viscous, 'viscous flow' is not the specific term for this smooth pattern.