Physical Thermodynamics and Fluids Flashcards
What is the definition of heat?
Transfer of non-mechanical energy between a system and its environment.
What is heat related to ?
Total thermal energy of an object
What does an extensive property mean?
Extensive property means that it depends on the mass of the material
What is the formal definition of temperature?
it is the macroscopic measure of the average internal (thermal) energy of a system.
Related to average kinetic energy of molecules
Does temperature depend on amount of material?
No, it is an intensive
Does adding heat always increase temperature?
No not always, phase change can also happens
Compare a huge glacier to a red hot piece of charcoal,
what is the charcoals thermal energy and temperature compared to the glacier?
Higher temperature, yes
Higher thermal energy, no
Thermal energy depends on
What is the Zeroth Law of Thermodynamics?
The zeroth law of thermodynamics describes thermal equilibrium. When two objects of different temperatures are put together, the heat will flow until the objects have the same temperature
What are the three modes of heat transfer?
1) Conduction:
heat transfer through solids in contact (refer back to equation sheet)
2) Convection:
heat transfer via fluid circulation
(density differences)
3)Radiation
heat transfer by emission/absorption of electromagnetic energy
Why is an oven mitt useful?
What types of heat transfer is an oven mitt trying to prevent?
It is trying to prevent conduction.
In this case, length is increased, and K is decreased
If you add heat to something, what are the possible effects?
1) temperature increase
2) phase changes
3) Things can expand (on a hot summers day, pressure increases in tires can increase, decrease in the winter.
What does a closed system mean?
A closed system means an object that does not exchange matter with a system, but can exchange heat.
What does the internal energy of a closed system depend on?
The energy transfer into the system and the the work the system does on its surroundings.
What is work?
Work is the amount of force appliedover distance
Thereby, what would the formula for internal energy/change in internal energy be?
change in energy= heat energy added (Q)-Work done (W)
What is heat related to?
total thermal energy of an object
What is thermal energy?
Thermal energy is the energy in an object that gives is related to it’s temperature.
It is the measure of the total kinetic energy in a molecule
What is heat?
Heat is the transfer of thermal energy.
How are temperature and thermal energy related?
Temperature and thermal energy are related as thermal energy can affect temperature.
However, they are different in that thermal energy depends on the mass of an object, while temperature does not depend on the mass of an object.
Temperature is a measure of the average kinetic energy, while thermal energy is the measure of all the kinetic energy in a mass.
Thereby thermal energy is dependent on mass.
What is the internal energy of a system?
The total overall energy in a system. (Potential energy+kinetic energy+ chemical bond energy+ any other types of energy in a system)
How can you measure the change of internal energy in a system?
Delta E= Q-W
where Q= heat added to the system
W= the work done by system
This is the also the first law of thermodynamics.
Ideal gas law:
PV=nRT
what are the variables in the ideal gas law called (one term)
state variables
If two gases have the same state variables at the same time, they are called:
identical, in the same state
In pressure volume graphs, if an ideal gas changes from one combination of state variables to a different combination of state variables, that means that the:
that a thermodynamic process has happened.
Involves adding or subtracting thermal energy, adding work, or both.
However, no matter how you get to a different state, the total change in internal energy is the same.
What are the terms, respectively for constant pressure, constant volume, constant temperature, an no heat exchange.
1) Isobaric
2) Isochoric (tire example)
3) Isothermal (constant temperature)
4) Adiabatic (no heat transfer)
What is pressure?
it is a Force distributed over an area
What are the units?
Pascals
Units: (N/m^2)
Scalar
1 atm is qual to how many pascals?
100 pascals
Will increasing the temperature of a gas in a confined spaces increase in pressure?
Yes.
Does a gas in a closed container with a frictionless piston, when is given heat and moves piston upwards, do any work?
Work is Force times Distance.
Did pressure increase: yes, so force has increased
Did Piston’s distance change?:yes
So, yes the gas did do work.
For the work done by a gas, what is the equation?
It is
Work= (Pressure)(change in Volume)
this can be rearranged to
Work= (Force/area)(change in Volume)
Why is a piston and a closed container called an isobaric process?
It is called an isobaric process as the volume is changed to equalize any changes in pressure
In a pressure (y axis) vs volume diagram, what would an isobaric process where the gas is heated and causes the piston to go up look like increase look like?
It would be a straight line (horizontally)
Isobars are flat line
How can we change our first law of thermodynamics be changed so that it can explain isobaric processes?
Keep pressure constant, and change volume”
Change in internal energy= (Head added or taken away )-P(change in volume)
Where as before it was
Delta E=Q-W
In an isochoric system (constant volume), what happens when heat is transferred to the system?
The heat will increase the pressure of the system, but the volume will not change
This would cause a straight vertical line on a P vs V graph.
In an isochoric system, is any work done by the gas?
No, as the container does not change in volume
What does the first law energy look like in isochoric processs?
They are: Change in energy= Heat added or taken away
In an isothermal process: the — stays constant
temperature
How to you make a system isothermal?
You put your system in a large water bath in order to prevent large changes in kinetic energy, and thereby
In an isothermal system, that will happen when you lift the piston in a closed container?
The pressure decreases, and a result.
Moles of gas stays the same, so heat flows into the system into the gas from the outside reservoir to prevent the temperature from changing.
What kind of line would the above scenario produce on a pressure vs volume graph?
Since volume increase, and pressure decreased, the arrow would sloped downwards with a curve.
What is the change in energy for the isothermic system?
It is zero, as no work is done, and the kinetic energy does not change at all, as the temperature does not change.
If temperature does not change, the average kinetic energy .total energy does not change.
In an adiabatic system, you take move up a piston. What will happen to the system?
When piston moves up, pressure is reduced, and as a result temperature is reduced as well. However, since you cannot do a heat transfer, you cannot increase the temperature and average kinetic energy.
In an adiabatic system, what does the P vs V graph look like?
It is a downwards sloping line with a curve, but the curve is steeper.
What is the change in energy in the system?
Change in energy= -Work
work is negative as the work is done on the system, rather than by the system
In a P vs V diagram, what would you need to do to find amount of work?
You use the area under the curve.
Also understand negative and positive work based on the type of work done (by or on the system), and whether change in volume is negative vs positive
What is entropy?
The disorder of a system
What is the 2nd law of thermodynamics?
Entropy either increases or stays the same in a closed system.
However, the universe of a system increases as a whole.
Entropy of a closed system can increase, only if the entropy of the surrounding system:
increased.
In a thermodynamic cycles, it is—– to convert all heat into work
impossible
Is the human body a closed system, open system, or isolated system?
Human body can exchange matter from outside, is influences by external variables, so it is not an isolated system, rather an open system.
What is an open system, closed system, and isolated system?
open: can exchange matter and energy,
closed: only energy, not matter,
isolated: no matter or energy exchange
How do humans exchange energy with environment?
You can conduct energy by touching things and conducting energy
How do humans exchange energy with environment?
Eating, pooping, breathing, ect.
What is the formal definition of a fluid?
The formal definition of a fluid is a material that flows/ takes shape of its container when at rest
Is a gas a fluid?
yes
Density equation is:
density = (mass/volume)
(kg/m3)
What is specific gravity?
Ratio of density to density of water
What is the density of water?
Density of water is: 1000kg/m3
or 1g/cm3
Does specific gravity have units?
no
Weight of a fluid is:
W=mg
W=(Density)Vg
What is hydrostatic gauge pressure?
Pressure due to being immersed within a fluid.
A gage is zeroed at the surface of a fluid.
What is the formula for P (gauge)
P (gauge)= pfluid(g)(D)
pfluid: density of fluid
D: diving depth
g: (gravity)
What is the TOTAL pressure that a diver feels?
P(total)=P(surface)+P(gauge pressure)
On the P vs depth graph, what kind of curve does the gauge pressure have?
P=(p)(g)(D)
Do linearly upwards graph
What is buoyant force?
The upwards force exerted on an object partially or completely submerged into an object due to the difference pressure between the top and bottom of the object.
What is archimedes principle?
Fb= pfluid(Vsubmerge)(g)
Why do helium filled balloons rise while air filled balloons sink?
Helium Buoyant force
What is the equation for flow-rate?:
f=m3/s
f=(area)(flow speed)
What is continuity?
Continuity is the concept that for an incompressible fluid, flow rate is constant throughout a pipe
What is the relation between area and flow rate for a continuous fluid?
A1V1=A2V2
What is ideal fluid flow?
1) incompressible (density is constant)
2) can’t be viscous
3) laminar flow (straight flowing)
4) flow rate is steady
What would be examples of violations of ideal fluids?
1) compressed gas
2) flow of viscous fluids
3) air turbulence in storms
What is the formula that describes ideal fluid flow?
Bernoulli’s Equation
At any two points of equal height, faster fluid flow =
lower pressure
Why might the roof fly off during a tornado?
The speed of airflow above lowers the pressure so much above than below, that will cause roofs to fly off.
Any fluid exposed to the atmosphere is at —— pressure.
atmospheric
The capillaries are much smaller than the aorta, so is the blood flow in the faster?
There are so many capillaries, that they have a greater overall effective surface area than the aorta.
How do blood pressures in the arms and legs of humans differ?
Studies shows they are comparable.
How does the speed in those two differ?
The femoral artery vs the aorta are about the same, so speed is comparable.
We know pressure, speed, so take those constants out.
When we do,
pgy(1)=pgy(2)
assuming p and g are the same.
So this experiment is saying your area and leg are in the same height.
So basically, physics doesn’t explain this. Sooo… Bernouille’s principle is wrong in this, as blood is not an ideal fluid.
Why is blood not an ideal?
Flow rates are not equal
There is not laminar flow
Blood is a little bit viscous.
