Chapter 7 - Fluids and Solids Flashcards
According to Archimedes’ principle, the bouyant force acting upon an object is equal to what?
the weight of the fluid displaced
What is the elastic limit of a solid?
It is the greatest stress a solid can take and still return back to its original state.
What is friction in a fluid called?
viscosity (η)
For a floating object, relative densities = what?
% submerged
What are the units of viscosity?
N x s/m2
What is meant by an elastic solid?
With an applied force, a solid can be bent, compressed, or stretched, but can return to its original state when the force is removed.
How does surface tension affects surface area?
As surface tension increases, its surface decreases in area.
Equation: Archimedes’ principle of bouyancy
B = ρfluid x Vfluid displaced x g
Equation: viscous retarding force
F = 4πηLv
Which materials are most prone to lateral shear?
crystalline solids
Define a solid
a material that can hold a definite shape
What is the difference between stress and strain?
Stress causes a strain (deformation).
What is the characteristic of brittle materials in terms of strain and stress?
Their ultimate tension strengths are close to their fracture stress. They tend to fracture, without deforming much.
Equation: Reynolds number (NR)
NR = 2ρvR/η
R = radius of vessel
Define a fluid
any matter that flows (liquids and gases)
What a material’s ultimate tension strength?
the point at which a material is under maximum stress
What is meant by turbulent flow?
If the flow of a fluid is sufficiently high, then a chaotic and irregular pattern develops in the fluid.
What are the units of density?
kg/m3
If the radius of a pipe is doubled, how does this affect the flow rate?
Flow rate increases by a factor of 16.
Describe pascal’s principle.
A pressure applied to an enclosed fluid is transmitted equally throughout the fluid and to the walls of the fluid’s container.
Equation: density
ρ = mass/volume
Equation: velocity of fluid at the center of a pipe
v = [(P1 - P2)/4ηL] r2
What is the characteristic of ductile materials in terms of strain and stress?
They have fracture strains far above their ultimate tension strength. They deform a lot before they fracture.
Equation: strain (ε)
Strain = ε = change in dimensional length/original dimensional length = ΔL/L
What are the units of pressure?
pascal (Pa) = N/m2
Equation: specific gravity/relative density
specific gravity = ρrelative = ρmaterial/ρH2O at 4ºC
Equation: Pascal’s principle of pressure
P1 - P2 = ρ(y2 - y1)g
When does a solid material become fractured?
when strain is increased beyond a solid’s maximum tension strength
Equation: Bernoulli’s equation relating fluid pressures (2 versions)
P1 +1/2ρv12 + pgy1 = P2 + 1/2ρv22 + pgy2
k = Pagainst inner walls + 1/2ρv2 + ρgh
If an object has a greater bulk modulus (B), what does this say about its ability to deform?
It does not deform easily. Its volume remains mostly unchanged (cyrstalline solids).
As a simple fluid flows through a pipe, describe its flow rates near the edges versus the center.
Fluid in the center of the pipe flows the fastest, while fluid at the edges of the pipe flows the slowest (speed is almost 0).
Equation: Poiseuille’s principle of flow rate (Q)
Q = (πr4/8ηL) (P1 - P2)
What are the units of stress?
N/m2
Equation: stress (σ)
Stress = σ = Force/Area
How do pressures and velocities of air differ above and below a plane’s wing?
The top of the wing is curved, so it is longer than the bottom. Air must move faster across the top, resulting in a decreased pressure compared to the bottom of the wing. This allows lift.
If a cross-sectional area is smaller at the beginning of a pipe than the cross-sectional area at the end, how do the speeds of the fluid compare?
At the beginning, the speed with be faster than at the end.
Equation: continuity of flow rate
Q = A1V1 = A2V2
For sunken objects, relative densities = what?
W/Fbouyant ratio
Equation: flow rate (Q) in terms of volume
Q = V/t
Equation: pressure
P = F⊥/A
Equation: Bulk moldulus (B)
B = -ΔP/(ΔV/V0)
When is a solid material plastically deformed?
when it has passed its elastic limit
Stress-strain graph
What numbers correspond to laminar or turbulent flow?
Laminar: NR < 2000
Turbulent: NR > 3000
Unstable: 2000 > NR > 3000
What is meant by laminar/streamline flow?
Adjacent layers of a fluid have the ability to slide past one another in a smooth and uniform fashion.
If a cross-sectional area is smaller at the beginning of a pipe than the cross-sectional area at the end, how does the flow rate of the fluid compare?
It is the same along the entire pipe.
Equation: Young’s modulus Y of a solid’s elasticity
E = Y = Stress/Strain = σ/ε = (F/A)/(ΔL/L)
What is meant by bulk deformation and what is the result?
As pressure increases on all sides of an object, the object decreases in volume.
How does temperature change affect the viscosity of a liquid and gas?
As temperature increases, fluid viscosity decreases, while gaseous viscosity increases.
Equation: cross-sectional area of a pipe
A = πr2
When fluid velocity increases in a pipe, how is pressure affected?
Pressure will decrease.
