Fluids Flashcards
Liquid
ability to flow and conform to the shapes of their containers
Gases and liquids are….
Fluids
Only solids can withstand ____ forces, but both fluids and solids can exert _____ forces.
shear/tangential
perpendicular
Density
scalar
p = m/v
g/mL or kg/m^3 or g/cm^3
1 g/cm^3 = _____ kg/m^3
1000
Weight of any Volume
Fg = density * volume * gravity
Specific Gravity
density of a fluid compared to pure water @ 1 atm and 4 C
SG = density / 1(g/cm^3)
Pressure
ratio of magnitude of force per unit area in pascals
P = F/A
scalar
1 atm = ____ torr = _____ mmHg = 1.013*10^5 Pa
760
760
1 Pa = _____ N/m^2
1
Atmospheric Pressure
changes with altitude
impacts a number of processes including hemoglobins affinity for oxygen and boiling of liquids
Absolute (Hydrostatic) Pressure
total pressure exerted on an object submerged within a fluid
P = Po + pgz
Po = ambient pressure (pressure at surface)
p = density
z = depth of object
In open air and most situations Po = _____ but in other fluid systems the surface pressure may be higher or lower than atmospheric pressure.
1 atm
Pressure cooker increases ____ to raise the ___ of water in food to reduce cooking time and prevent loss of moisture.
pressure
boiling point
Gauge Pressure
difference between absolute pressure inside tire and armspheric pressure outside the tire
Pgauge = P - Patm = (Po + pgz) - Patm
Hydrostatics
study of forces and pressures acting on fluids at rest
Pascals Principle
an incompressible fluid with a change in pressure will have it transmitted through every portion of the fluid and the walls of the containing vessel
Hydraulic Systems
take advantage of the near-incompressibility of liquids to generate mechanical advantage (pascals theory)
pressure is same across both piston areas, so forces are proportional based in ratio of areas
P = F1/A1 = F2/A2
F2 = F1 (A2/A1)
Piston Displacement of Hydraulic systems
energy is conserved as volume displaced by piston 1 is equal to volume displaced in piston 2
V = A1d1 = A2d2
d2 = d1(A1/A2)
Work Generated by Piston Hydraulic Systems
W = P*delta V = F/A (Ad)
W = F1d1 = F2d2
greater force through smaller distance
Archimedes Principle
buoyancy of objects when placed in a fluid
any object placed in a fluid will cause a colume of fluid to be displaced equal to the volume of the object submerged
a body wholly/partially immersed in a fluid will be buoyed upwards by a force equal to the weight of the fluid it dispalces
Buoyant Force
mass of fluid dispersed exerts a force equal to its weight against the submerged object
F = pfluid * Vfluid displaced * g = pfluid * Vsubmerged*g
When an object is placed in a fluid, it will sink into the fluid only to the point at which the _________ exerts a force equal to the ________
volume of displaced fluid
weight of object
If two objects placed in a fluid displace the same volume of liquid, they will experience ________ even if the objects themselves have different masses.
same magnitude of buoyant force
Specific Gravity and how much a floating object lies below the surface
if an objects specific gravity is expressed as a percent, it indicates the percent of the objecy submerged:
ie. ice density if 0.92 g/cm^3 so its specific gravity is 0.92 and 92% of it is submerged
A specific gravity of exactly 1 indicates that _____
100% of the object will be submerged but it will not sink
Surface Tension
results from cohesion
molecules have strong attractive forces on the molecules below them pulling surface of the liquid toward the center to produce the tension with a net upward force.
Cohesion
attractive force between molecules of liquid towards other molecules of same liquid
Adhesion
attractive force of liquid molecules to molecules of other substance
Meniscus
downward curved surface which forms when adhesive forces greater than cohesive
Convex Meniscus
Middle higher than the edges
cohesive forces greater than the adhesive forces
Fluid Dynamics
study of fluids in motion
Assumptions For Fluid Dynamics
1) rigid walled containers
2) uniform density of fluids
Viscosity
resistance of a fluid to dlow
Pascal-second = N*s / m^2
Viscous Drag
caused by increased viscosity which is a non conservative force like air resistance
Inviscid
fluids which have no viscosity
More viscous fluids will _____ more energy while flowing.
lose
Laminar Flow
smooth and orderly, layers of fluid flow parallel to each other; HOWEVEr layers will not always have same linear speed
ie: layers close to wall of pipe flow slower than those in the center
Posielles Law
with Laminar Flow in a confined space, rate of flow can be calculated
Q = (pi*r^4 *delta pressure gradient)/ (8 * viscosity * Length)
***relationship of radius and pressure gradient is incerse exponential to the fourth power ; even a slight change in radius can effect the pressure gradient
Turbulence Flow
rough and disorderly
forms eddies
Eddies
caused by turbulence flow; swirls of fluid of varying sizes occuring downstream of an obstacle
Critical speed
when turbulence occurs in unobstructed fluid flow
depends on physical properties of the fluid like viscosity/diameter
Vc = (reynolds number * viscosity )/ (density *diamerter)
Boundary Layer
when critical speed is exceeded, laminar flow occurs only in fluid adjacent to the wall
Reynolds number
depends on size, shape and surface roughness of an objects within the fluid
Streamlines
pathways followed by fluid eleents/particles as they move
velocity vector is tangent to the stram line and they don’t cross each other
Flow rate is ____ for a closed system and is ____ of changes in cross sectional area
constant
independent
Linear Speed
measure of linear displacement of fluid particles in a given amount of time
While the flow rate is constant, the linear speed of the fluid _______ to the cross sectional area
does not change relative
Continuity Equation :Q = v1A1 = v2A2
Q flow rate
v1 = linear speeds
A = cross sectional area
tells us fluids flow more quickly through narrow passages and slowly through wider onces
Bernoullis Equation
P1 + 1/2pv1^2 + pgh1 = P2 + 1/2pv2^2 + pgh2
P is absolute pressure of fluid
p is density of fluid
v is linear speed
h is heigh of fluid
sum of the staatic pressure and dynamic pressure will be constant within a closed contained for an incompressible fluid not experiencing viscous drag
Dynamic Pressure
pressure associated with movement of fluid
1/2pv^2
Static pressure
P + pgh
Venturi Flow Meter
pgh constant at both points
h difference is difference in heights of the columns
linear speed must increases as cross sectional area decreases
dynamic pressure increases, absolute pressure decreases making fluid at venturi tube lower
Circulatory system is a _____ with a _____ flow rate.
The ___ flow rate can be measured as a _____
closed loop
non constant
non constant
pulse
As blood flows away from the heart, each vessel has _____ resistance until the capillaries, but resistance total decreases as the vessels are ___ with each other.
increased
parallel
Return flow of blood to heart from skeletal muscles squeezing, _____ pressure in limbs to push blood to heart which has decreased pressure
increasing
Results of turbulent blood flow
heart murmurs
During inspiration, there is a ____ pressure gradient that moves air into lungs. During expatriation this gradient reverses.
When air reaches the alveoli it has ______
negative
essentially no
