Fluids Flashcards
substances that have the ability to flow and conform to the shape of their containers; can exert perpendicular forces but not shear; liquids and gases are considered this
fluids
do not flow and they retain their shape regardless of their containers
solids
mass per unit volume of a substance
density (ρ)
density (ρ)
ρ = m/V
measure of force per unit area; it is exerted by a fluid on the walls of its container and on objects placed in fluid; scalar quantity; gas always exerts perpendicular to walls of container
pressure
pressure
P = F/A
sum of all pressures at a certain point within a fluid; equal to pressure at surface of a fluid (usually atmospheric) plus pressure due to fluid itself
absolute pressure
absolute pressure
P = P(o) + ρgz
where: P(o) = incident/ambient pressure (at surface) ρ = density g = acceleration due to gravity z = depth of object
difference between absolute pressure and atmospheric pressure
gauge pressure
gauge pressure
P(gauge) = P - P(atm) = (P(o) + ρgz) - P(atm)
where: P(o) = incident/ambient pressure (at surface) ρ = density g = acceleration due to gravity z = depth of object below some point
the study of fluids at rest and the forces and pressures associated with standing fluids
hydrostatics
states that a pressure applied to an incompressible fluid will be distributed undiminished throughout the entire volume of the fluid
Pascal’s principle
operate based on the application of Pascal’s principle to generate mechanical advantage
hydraulic machines
principle that governs buoyant force
Archimede’s principle
when an object is placed in a fluid, the fluid generates a force against the object that is equal to the weight of the fluid displaced by the object; direction is always opposite to the direction of gravity
buoyant force
when max force is larger than force of gravity on object the object will _____; true if object is less dense than fluid it is in
will float
when max force is smaller than force of gravity on object the object will _____; true if object is more dense than fluid it is in
will sink
causes liquid to form a thin but strong layer at liquid’s surface, caused by cohesion
surface tension
attractive force that a molecule of liquid feels toward other molecules of the same liquid
cohesion
attractive force that a molecule of liquid feels toward the molecules of some other substance
adhesion
the study of fluids in motion
fluid dynamics
a measurement of a fluid’s internal friction
viscosity (η)
a nonconservative force generated by viscosity; analogous to air resistance
viscous drag
smooth and orderly flow of fluid; often modeled as layers of fluid that flow parallel to one another, layers will not have same linear speed
laminar flow
relationships that determine rate of laminar flow
Poiseuille’s law
Poiseuille’s law
Q = (π (r^4) ΔP) / (8ηL)
where: Q = flow rate r = radius of tube ΔP = pressure gradient η = viscosity L = length of pipe
rough and disorderly flow of fluid; when unobstructed, turbulence can arise when the speed of the fluid exceeds a certain critical speed
turbulent flow
critical speed (V(c))
V(c) = (N(R) η) / (ρD)
where: N(R) = Reynold's number η = viscosity ρ = density D = diameter of tube
volume per unit time; is constant for a closed system and independent of changes in cross-sectional area
flow rate
measure of linear displacement of fluid particles in a given amount of time; does change relative to ross-sectional area
linear speed
expression of conservation of mass; tells us that fluids will flow more quickly through narrow passages and more slowly through wider ones
continuity equation
continuity equation
Q = v(1) * A(1) = v(2) * A(2)
where:
Q = flow rate
v = linear speed
A = cross-sectional area
an expression of conservation of energy; states that sum of static pressure and dynamic pressure will be constant between any two points in a closed system
Bernoulli’s equation
Bernoulli’s equation
P(1) + 1/2 ρv(1)^2 + ρgh(1) = P(2) + 1/2 ρv(2)^2 + ρgh(2)
where: P = absolute pressure ρ = density v = linear speed g = acceleration due to gravity h = height of fluid above some point
term of Bernoulli’s equation associated with movement; kinetic energy divided by volume
dynamic pressure
dynamic pressure
1/2 ρv^2
term of Bernoulli’s equation that is same as equation for absolute pressure: ambient pressure + (potential energy / volume)
static pressure
static pressure
P + ρgh
refers to how the velocity of a fluid passing through a constricted area will increase and its static pressure will decrease
Venturi effect
behaves as a closed system with nonconstant flow in the body; is a closed loop
circulatory system
decreases as total cross-sectional area increases
resistance
primary driver of arterial circulation
heart
has three times the volume of arterial circulation and is motivated by the skeletal musculature and expansion of the heart
venous circulation
_____ and _____ create a pressure gradient not only for the respiratory system, but for the circulatory system as well
inspiration and expiration
air that has essentially zero speed in the body
air at the alveoli
