concept 4b Flashcards
fluids
characterized by their ability to flow and conform to the shapes of their containers
both liquids and gases are fluids
can impose large perpendicular forces, falling water from significant height is painful
solids
do not flow and are rigid enough to retain a shape independent of their container
can also exert forces perpendicular to their surfaces
but solids are able to withstand shear (tangential) forces
density
ratio of their mass to their volume scalar quantity, has no direction p=m/V p is rho and represents density units are kg/m^3 or g/mL or g/cm^3 1g/cm^3=1000kg/m^3
finding weight using density
with known density at any volume you can calculate weight
Fg=pVg
this is the calculation that appears when working through buoyancy problems
specific gravity
ratio of an object’s density to the density of water
comparing the density of a fluid to pure water at 1 atm and 4 deg C (which is 1 g/cm^3 or 1000 kg/m^3)
SG=p/(1 g/cm^3)
this is unitless and expressed as a decimal
can be used to determine if an object will sing or float in water
pressure
ratio of force to the area over which it is applied
scalar quantity
measured in pascals (Pa), millimeters of mercury (mmHg) or torr, or atmospheres (atm)
P=F/A
1 Pa= 1 N/m^2
units of pressure
1.013e5 Pa 760 mmHg 760 torr 1 atm these are the equivalent measures of pressure
atmospheric pressure
pressure of the atmosphere
changes with altitude
impacts a number of processes, including hemoglobin’s affinity for oxygen and boiling of liquids
absolute pressure
the actual pressure at a given depth in a fluid
including both ambient pressure at the surface and the pressure associated with increased depth in the fluid
aka hydrostatic pressure
total pressure exerted on an object that is submerged in a fluid
P=Po+pgz
P is absolute pressure, Po is the incident or ambient pressure, p is density of fluid, g is accel due to gravity, z is depth of object
ambient pressure
the pressure at the surface
aka incident
gauge pressure
the difference b/w the absolute pressure inside a tire and the atmospheric pressure outside the tire
amount of pressure in a closed space above and beyond atmospheric pressure
Pg=P-Patm=(Po+pgz)-Patm
hydrostatics
study of fluids at rest and the forces and pressures associated with standing fluids
Pascal’s principle
states that pressure applied to a non compressible fluid is distributed equally to all points within that fluid and the walls of the container
P=F1/A1=F2/A2
hydraulic system
a simple machine that exerts mechanical advantage using an incompressible fluid
based on Pascal’s principle and conservation of energy
Archimedes’ principle
states that a body immersed in a volume of fluid experiences a buoyant force equal to the weight of the displaced fluid
F(buoy)=p(fluid)V(fluid displaced)g
=p(fluid)V(submerged)g
remember to always use the density of the fluid itself not the density of the object
buoyancy
the upward force that results from immersion in a fluid
described by Archimedes’ principle
will an object float or sink?
an object will FLOAT if its average density is less than the average density of the fluid it is immersed in
an object will SINK if its average density is greater than that of the fluid
molecular forces in liquids
surface tension
cohesion
adhesion
surface tension
the result of the cohesive forces in a liquid creating a barrier at the interface b/w a liquid and the environment
causes the liquid to form a thin but strong layer like a “skin” at the liquid’s surface
exp. dome the forms on top of penny
cohesion
the attractive force that a molecule of liquid feels toward other molecules of the same liquid
liquids will stick together
intermolecular force b/w molecules of liquid
adhesion
the attractive force that a molecule of liquid feels toward molecules of some other substance
intermolecular force b/w molecules of a liquid and molecules of another substance
liquids will stick to other substances
exp. water climbing up a paper towel
meniscus
curved surface in which liquid “crawls” up the side of the container a small amount
will form when the adhesive forces are greater than the cohesive forces
backwards (convex) meniscus
the liquid level is higher in the middle than at the edges
occurs when the cohesive forces are greater than the adhesive forces
Mercury (only metal that is liquid at room temp) forms one when placed in a container
fluid dynamics
the study of fluids in motion
in many aspects of life, delivery of water to our homes and blood flow thorough our arteries and veins
viscosity
the resistance of fluid flow
increased viscosity of a fluid increases its viscous drag
thin fluids, gases, water, dilute aqueous solutions, have low viscosity and flow easily
whole blood, vegetable oil, honey, cream, molasses are thick fluids and flow slowly
viscous drag
nonconservative force that is experienced with high viscosity
analogous to air resistance
laminar flow
smooth and orderly movement of fluids
often modeled as layers of fluid that flow parallel to each other
low viscosity fluids have low internal resistance and have laminar flow
Poiseuille’s law
relates viscosity, tube dimensions, and pressure differentials to the rate of flow b/w 2 points in a system
allows to calculate laminar flow
Q=(pir^4delta P)/8nL
Q is flow rate, r is radius of the tube, delta P is the pressure gradient, n (eta) is viscosity, and L is length of pipe
even small change in radius has significant effect on pressure gradient, assuming constant flow rate
turbulent flow
rough and disorderly movement of fluids
causes the formation of eddies
also can arise in unobstructed flow if speed of fluid exceeds a critical speed
eddies
swirls of fluid of varying sizes occurring typically on the downstream side of an obstacle
caused by turbulent flow
critical speed
depends on the physical properties of the fluid, viscosity and diameter of tube
when speed of fluid exceeds critical speed fluid demonstrates complex flow patterns and laminar flow occurs only in thin layer of fluid adjacent to the wall, boundary layer
calculating critical speed
vc=N(R)n/pD
N(R) is Reynolds number a constant, n is viscosity, p is density, and D is diameter of tube
Reynolds number
depends on factors such as size, shape, and surface roughness of any objects within the fluid
streamlines
representation of molecular movement
indicate the pathways followed by tiny fluid elements (fluid particles) as they move
never cross each other
velocity vector of fluid particles will alway be tangential to the streamline
flow rate
rate of movement of fluids
volume per unit time
is constant for a closed system and is independent of changes in cross-sectional area
linear speed
measure of the linear displacement of fluid particles in a given amount of time
the product of linear speed and area are equal to flow rate
Q=v1A1=v2A2
Q is flow rate, v is linear speed of fluid at points and A is area at points
linear speed will increase with decreasing cross-sectional area
continuity equation
Q=v1A1=v2A2
it tells us that fluids will flow more quickly through narrow passages and more slowly though wider ones
and flow rate is constant
Bernoulli’s equation
an equation that relates static and dynamic pressure for a fluid to the pressure exerted on the walls of the tube and the speed of the fluid
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, g is accel due to gravity, and h is height of fluid
dynamic pressure
1/pv^2
pressure associated with movement of fluid
essentially kinetic energy of the fluid divided by volume
static pressure
P+pgh
same equation for absolute pressure
pgh is similar to gravitational potential energy and is pressure associated with the mass of fluid sitting above some position
energy density
ratio of energy per cubic meter
pressure can be thought of as this
systems at higher pressure have a higher energy density than systems at lower pressure
pitot tubes
specialized measurement devices that determine the speed of fluid flow by determining the difference b/w the static and dynamic pressure of the fluid at given points along the tube
Venturi flow meter
application of Bernoulli’s equation
tube that starts wide and becomes narrow with tubes connected
as tube narrows the linear speed increases
thus the pressure exerted on the walls decreases causing the column about the tube to have a lower height
Venturi effect
describes the relationship b/w the continuity equation and Bernoulli’s equation
as cross-sectional area of the tube decreases, the speed of fluid increases, and the pressure exerted on the walls of the tube decreases
circulatory system
is a closed loop that has a non constant flow
this flow is a result of valves, gravity, physical properties of our vessels (elasticity), and mechanics of the heart
measured and felt as a pulse
there is a loss of volume from circulation as result of osmotic and hydrostatic pressure
blood volume entering the heart always equals blood volume leaving the heart during single cycle
blood leaving the heart
each vessel has a progressively higher resistance, but total resistance of the system decreases bc increased number of vessels in parallel with each other
similar to parallel resistors in circuits, equivalent resistance is lower for capillaries in parallel than in the aorta
blood returning to the heart
facilitated by mechanical squeezing of skeletal muscles which increase pressure in the limbs and pushes blood to the heart
expansion of the heart decreases pressure in the heart and pulls blood in
venous circulation holds approximately 3 times as much blood as arterial circulation
pressure gradients
pressure gradients created in the thorax by inhalation and exhalation motivate blood flow
heart murmurs
result from structural defects of the heart
heart because of turbulent blood flow
respiratory system
mediated by changes in pressure
follows the same resistance relationship as the circulatory system
when air reaches the alveoli it has essentially no speed
inspiration
there is a negative pressure gradient that moves air into the lungs
breathing air in
expiration
there is a positive pressure gradient that moves air out of the lungs
opposite of inspiration
breathing air out
phase
or state
different physical forms that matter can exist in
gas, liquid, and solid
gas phase
display similar behavior and follow similar law regardless of their particular chemical identities
classified as fluids bc can flow and take on the shapes of their containers
atoms move rapidly and are far apart from each other
only weak intermolecular forces exist b/w gas particles
ability to expand to fill any volume
easily compressible, distinguishes them from liquids
gas variables
pressure (P)
volume (V)
temperature (T)
number of moles (n)
sphygmomanometers
medical devices that measure blood pressure
measure in mmHg
standard temperature and pressure (STP)
conditions of 273 K (0 deg. C) and 1 atm
many processes involving gases take place under these conditions
are not identical to standard state conditions
usually used for gas law calculations
standard state conditions
conditions of 293 K, 1 atm, and 1M concentration
used when measuring standard enthalpy, entropy, free energy changes, and electrochemical cell voltage
ideal gas
represents a hypothetical gas with molecules that have no intermolecular forces and occupy no volume
real gas
deviate from the ideal gas behavior at high pressures (low volumes) and low temperatures
many compressed real gases demonstrate behavior close to ideal
ideal gas law
PV=nRT
P is pressure, V is volume, n is number of moles, T is temperature, and R is the ideal gas constant
can be used to describe the behavior of many real gases at moderate pressures and temperatures significantly about absolute zero
ideal gas constant (R)
8.21e-2 Latm/molK
units are based on the units of the variables given in the passage or question
density
p=m/V=PM/RT
m is mass, V is volume, P is pressure, M is molar mass, R is gas constant, T is temp
combined gas law
gas law that combines Boyle’s law, Charles’s law, and Gay-Lussac’s law
states that pressure and volume are inversely proportional to each other and each is directly proportional to temperature
P1V1/T1=P2V2/T2
Avogadro’s principle
states that all gases at a constant temperature and pressure occupy volumes that are directly proportional to the number of moles of gas present
n/V=k
n1/V1=n2/V2
k is a constant, n is number of moles, V is volume
*as the number of moles of gas increases, the volume increases in direct proportion
Boyle’s law
states that at constant temperature, the volume of a gaseous sample is inversely proportional to its pressure
PV=k
P1V1=P2V2
pressure and volume are inversely related
when one increases the other decreases
Charles’s law
states that the volume of a gas at constant pressure is directly proportional to its absolute (kelvin) temperature
V/T=k
V1/T1=V2/T2
volume and temperature at directly proportional
when one increases, the other increases
Gay-Lussac’s law
states that the pressure of a gaseous sample at constant volume is directly proportional to its absolute temperature
P/T=k
P1/T1=P2/T2
pressure and temperature at directly proportional
when one increase, the other increases
partial pressure
the pressure that one component of a gaseous mixture would exert if it were alone in the container
Pa=XaPt
Xa=(moles of gas A)/(total moles of gas)
Pa is partial pressure of gas a, Xa is mole fraction, Pt is total pressure in container
Dalton’s law of partial pressures
states that the total pressure of a gaseous mixture is equal to the same of the partial pressures of the individual components
Pt=Pa+Pb+Pc+…
Henry’s law
states that the mass of gas that dissolves in a solution is directly proportional to the partial pressure of the gas about the solution
[A]=k(h)*Pa
[A1]/P1=[A2]/P2=k(h)
[A] conc. of A in solution, k(h) is Henry’s constant, Pa is partial pressure of A
Henry’s constant depends on identity of gas
solubility of a gas will increase with increasing partial pressure of gas
vapor pressure
the pressure exerted by evaporated particles above the surface of a liquid
evaporation
dynamic process that requires the molecules at the surface of a liquid to gain enough energy to escape into the gas phase
kinetic molecular theory
theory proposed to account for the observed behavior of gases
considers gas molecules to be point like, volume-less particles exhibiting no intermolecular forces that are in constant random motion and undergo completely elastic collisions with the container or other gas particles
used to explain the behavior of gases
kinetic molecular theory assumption 1
gases are made up of particles with volumes that are negligible compared to the container volume
kinetic molecular theory assumption 2
gas atoms or molecules exhibit no intermolecular attractions or repulsions
kinetic molecular theory assumption 3
gas particles are in continuous, random motion, undergoing collisions with other particles and the container walls
kinetic molecular theory assumption 4
collisions b/w any 2 gas particles (or b/w particles and the container walls) are elastic, meaning that there is conservation of both momentum and kinetic energy
kinetic molecular theory assumption 5
the average kinetic energy of gas particles is proportional to the absolute temperature (in kelvin) of the gas, and it is the same for all gases at a given temperature, irrespective of chemical identity or atomic mass
KE=1/2mv^2=2/3k(B)T
k(B) is Boltzmann constant
Boltzmann constant
k(B)=1.38e-23 J/K
serves as a bridge b/w the macroscopic and microscopic behaviors of gases
root-mean-square speed (u)
u=sqrt[3RT/M]
R is ideal gas constant, T is temp, M is molar mass
used to find the average speed of a gas particle
the higher the temp, the faster the molecules move
the large the molecules, the slower they move
Maxwell-Boltzmann distribution curve
shows the distribution of gas particle speeds at a given temperature
diffusion
movement of molecules from high concentration to low concentration through a medium (air or water)
heavier gases diffuse more slowly than lighter ones bc of differing average speed
when gases mix with one another
Graham’s law
states that the rate of effusion or diffusion for a gas is inversely proportional to the square root of the gas’s molar mass
r1/r2=sqrt[M2/M1]
r are the diffusion rates, M are the molar masses
effusion
the flow of gas particles under pressure from one compartment to another thought a small opening
when a gas moves through a small hole under pressure
slower for larger molecules
real gas deviations
due to pressure
due to temperature
deviations due to pressure
at moderately high pressure a gas’s volume is less than would be predicted by the ideal gas law due to intermolecular attraction
at extremely high pressures the size of particles become relatively large compared to the distance b/w them, this causes the gas to take up a larger volume than would be predicted by the ideal gas law
deviations due to temperature
as temp is reduced toward its condensation point (bp), intermolecular attraction causes the gas to have a smaller volume than that which would be predicted by ideal gas law
the closer a gas is to bp the less ideally it acts
at extremely low temps gases will occupy more space than predicted by ideal gas law
van der Waals equation of state
one of several real gas laws
corrects for attractive forces and the volumes of gas particles, which are assumed to be negligible in the ideal gas law
(P+n^2a/V^2)(V-nb)=nRT
a and b are physical constants experimentally determined
a and b in van der Waals equation
a is the term for attractive forces b is the term for big particles smaller gases have smaller a larger molecules have large b if a and b are zero it is the ideal gas law
