Ch 12: Fluid Mechanics Flashcards
What is (average) density?
density = mass/volume
What is the SI unit of density?
kilogram per cubic meter
What is the specific gravity of a material?
the ratio of its density to the density of water at 4.0°C, which is 1000 kg/m³
When a fluid is at rest, it exerts a force _____ to any surface in contact with it.
perpendicular
If we think of an imaginary surface within the fluid, the fluid on the two sides of the surface exerts _____.
equal and opposite forces on the surface
What is pressure?
dF⊥/dA; if pressure is the same at all points, then p=F⊥/A
What is the SI unit of pressure?
the pascal, which is equal to 1 N/m²
What is atmospheric pressure?
the pressure of the earth’s atmosphere at sea level, which is 1 atm = 1.013E5 Pa
When an element of a fluid is at rest, the downward forces (_____) are equal to the upward force (_____).
force due to pressure on top of surface and weight of the fluid element; force due to pressure on the bottom of the surface
As you move upward in a liquid, pressure _____.
decreases
What is the equation for pressure difference between 2 points in a static fluid of uniform density?
p_2 - p_1 = -ρg(y_2 - y_1)
What is the equation for pressure at a given depth h if p_0 is at the surface of the liquid?
p = p_0 + ρgh
What is Pascal’s Law (conceptually)?
Pressure applied to an enclosed fluid is transmitted undiminished to every portion of the fluid and the walls of the containing vessel
What is Pascal’s Law (relating to hydraulic lift)?
If p is the same everywhere, then F1/A1 = F2/A2
What is gauge pressure?
excess pressure above atmospheric pressure; p - p_atm
What is absolute pressure?
total pressure (p); gauge pressure + atmospheric pressure
What is Archimedes’s Principle?
When a body is completely or partially immersed in a fluid, the fluid exerts an upward force on the body equal to the weight of the fluid displaced by the body
What is the buoyant force?
the upward force exerted by any fluid upon a body placed in it, equal to the weight of the displaced fluid
The surface of a liquid behaves like _____.
a membrane under tension
Why are raindrops spherical?
Surface tension; the molecules of water exert attractive forces on each other, and so surface molecules are drawn into the volume, minimizing surface area; Spheres have the smallest surface area to volume ratio, and so that is the resulting shape.
What are two properties of an ideal fluid?
It is incompressible (its density cannot change) and has no internal friction (no viscosity)
What is laminar flow?
Adjacent layers of fluid slide smoothly past each other and the flow is steady
What is turbulent flow and when does it occur?
There is no steady-state pattern; this occurs at sufficiently high flow rates, or when boundary surfaces cause abrupt changes in velocity, causing the flow to become irregular and chaotic.
What is the continuity equation?
A1v1=A2v2 for incompressible fluid; multiply by ρ for compressible fluid.
What is volume flow rate?
dV/dt = Av, the rate at which volume crosses a section of the tub
