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Physlet Problems:  Thermodynamics

Physlet Problems: Thermodynamics

Physlet problems that relate to thermodynamics.


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Franziska vonHerrath
21 years ago
This problem and its physlet animation is a good
attempt to visualize the fact that expansion through
heating is unique to each metal. However, the
animation could be improved by enlarging the
temperature scale, in order to provide for more
accuracy when estimating the temperature change in the
metal bar. Since it was mentioned what units position
and time were measured in, it could have been included
what units the temperature scale showed.

I enjoyed the animation of the growing bubble rising
to the surface of the liquid to burst. The counting
vertical position scale also aided in performing the
ratio computation. However, after carefully
performing the final to initial temperature ratio
calculation, I disagree with the featured result. I
calculated the ratio to be 6.05.

This animation clearly underlines the properties of
an ideal gas and is nicely done in a, however, purely
qualitative manner. Overall, I?m not sure that the
properties of an ideal gas need this kind of elaborate
illustration. Simple pictures would have sufficed.

The speed vs. time graph nicely illustrates the
changes in the speed of the molecules of the gaseous
substance but aids little in showing the average speed
of the molecules. This visualization could be improved
by displaying the average speed of the different
spheres at the end of the animation to assist in the
calculation of the average kinetic energy.

In this problem, a gas is compressed at constant
pressure and seemingly at the constant temperature of
0 *C. Since the container appears tight (no molecules
can escape), I can only ask how is this process
possible. The pressure should have been visualized in
a better manner. The gauge added more confusion than
it cleared up. More work needs to be done in order
for one to make sense of this problem.

Additional Problem 1)
I had a hard time changing the temperature of the gas
in theleft container in the running time provided.
The running time should be increased to counteract not
only this problem, but also in order for the system to
be allowed to come to equilibrium.

Additional Problem 2)
This physlet worked well and is a good illustration
of the distribution of speeds in a gas.

This site could benefit from a more detailed
description of the problems? initial conditions.
Furthermore, the given answers should be accompanied
by a few sentences of explanation. Overall, this site
needs serious improvement to warrant its use over or
even in addition to a generic textbook.
Donald Hornback
Donald Hornback (Student)
21 years ago
The material covered by this review are the problems 8.12.1 through 8.12.5 and
the two additional problems. I spent a couple of hours going though the
problems and my own books trying to figure them out. My overall response to the
physlets offered at this sight is lukewarm. The goal of providing an
interesting, interactive approach to physics is a worthy one; however, these
physlets sometimes fall short. The descriptions (setup) for the problems could
be improved by offering better framing assumptions for the situation. The
illustrations themselves are not as clear as they could be; embarrassingly, it
took me more than a few minutes to realize that that ?thing? in problem 8.12.4
is a pressure gauge. The potential for effective learning through these
physlets does exist, but I feel that the choice of problems and animations could
be improved upon.

The very first physlet, 8.12.1, explores thermal expansion of solid rods, the
point of which is to show that for rods of equal initial length an equivalent
change in temperature will result in an equivalent change in length. This
physlet was fine, though I would suggest making it more apparent or readily seen
that the change in lengths actually is equivalent, such as posting the position
change, perhaps as done in problem 8.12.2.
Physlet 8.12.2 gave me the most trouble of the lot. Assuming that we are to use
the ideal gas equation, I didn?t get their answer after playing with it for a
while. The idea for this physlet is a good one though.
Physlet 8.12.3 offers a brief and VERY qualitative view of kinetic theory and
does not offer anything beyond a similar textbook picture of the three
Physlet 8.12.4 is an uninteresting trick question, and it failed to illuminate
or illustrate for myself the equipartition theorem in a useful way. Should an
underlying assumption (if it be true) that the system is in thermal equilibrium
be stated for the reader? And if we are to use kinetic theory in the reasoning
for this physlet, does it seem in order based on the image of the container
Physlet 8.12.5 the container contains a gas (missing assumption: an ideal gas)
that has work done on it in a straightforward isobaric process.
Additional problem one. Again, I had some trouble with the interface, but
eventually I got it to work a bit, though I could not get the particles and
temperatures to do what the physlet says it can do. Increasing the running time
beyond 15 seconds would allow for changes to actually reach equilibrium and
make the physlet more interesting.
Additional problem two. Once I assumed that the units of temperature were
Kelvin, I arrived at the same answer employing a simple plug-and-chug from a
given formula. The interactive aspect of this problem is negligible. My
question is: how is this problem (and several of the others) any different than
problems found in any general physics textbook?
Ian Clark
Ian Clark (Student)
21 years ago
This site appears to be comprised entirely of introductory physics problems
centered around java applets. The applets produce cartoons illustrating
different concepts from introductory kinetic, and thermodynamic theory. My
first impression was that the site was a little long on cartoons and a little
short on physics. I believe that the argument for these physics related java
cartoons (physlets) is that they build a sense of physical intuition in a more
expedient fashion than does the traditional approach to physics education.
While I do certainly respect this argument I felt this site sacrificed too much
of the traditional rigor and provided too little in return. In its defense, the
sight is an extension of an introductory physics text and when used in
conjunction with this text it may well be quite illuminating. As a stand-alone
educational tool however I would not give it high marks.
Mechanically the site was well constructed and easy to navigate. The only
serious difficulty I found was in measuring objects in the animation frame.
Many of the problems call for the viewer to measure the physical dimensions of
an object in the animation and I found this process to be somewhat onerous. On
all of the applets reviewed left clicking the mouse while the cursor is in the
frame of the animation displays the x, y coordinates of the cursor. This
provided an effective but cumbersome means of measurement, and the only other
option was to count the tiny grid lines. Even using a 19-inch monitor, I found
squinting at those tiny increments to be rather painful.
The page I viewed linked to five problems and two additional problems below I
review each of the first five in turn.

Problem 1.
Physical Principal Illustrated: the linear dependence of the thermal expansion
of solids on the change in temperature.

The Problem: three animations depict a little stick expanding as the temperature
rises from -50C to 0C (first animation), 0C to 50C(second animation), and 50C
to 100C (last animation). All sticks have the same initial and final length.
The viewer is asked if the three sticks are all the same material.

Review: This problem was well crafted in that it illustrated the dependence of
expansion on the change in temperature rather than the temperature its self (at
least at this level of theory). That being said I do have a fine point on which
to quibble. I personally would have replaced the phrase 'the same material'
with 'the same average coefficient of linear expansion'. Deciding that two
items are comprised of the same material because they have similar thermal
expansion characteristics seems somewhat analogous to deciding that a Ferrari is
made of the same material as a red delicious apple because they are roughly the
same color.

Problem 2
Physical Principal Illustrated: The ideal gas law

The Problem: A bubble rises from 5cm below the surface of the water to the
surface of the water. The viewer is asked to determine the ratio of final to
initial temperatures.

Review: I would really like to see something like 'expands adiabatically'
somewhere in the wording of this problem. The time frame is 1 second and as
such a lack of heat exchange with the water is probably a very good
approximation. Again this is a small point and in second semester physics the
possible error due to heat exchange would never have never crossed my mind.
I worked through this problem twice and I don't seem to be arriving at the same
answer that is presented on the page. The equation I derived was:

Tf/Ti = (Pf rf^3)/(Pi ri^3)

Where T, P, and r represent the temperature, pressure and the radius of the
bubble respectively, f indicates the final state and I indicates the initial
state. Using 101325 Pa and 101325 Pa + (density of H2O) (g) (h) for the final
and initial pressures and the dimensions given yields 18.2 rather than the 13.6
listed on the site. If I have made some error in mycalculations I would like
to be informed of the fact so that I can write a retraction. I can be contacted
at itc1@humboldt .edu.

Problem 3
Physical Principal Illustrated: the characteristics of the ideal gas.

The Problem: Three animations are displayed. The reader has to decide which
animation is depicting an ideal gas.

Review: Vibrantly illustrates the internal properties of an ideal gas i.e. no
interaction between particles, inter-particle distance is large with respect to
particle size, and perfectly elastic collisions with the container walls. This
was probably the most educationally effective use of applets I found on this

Problem 4
Physical Principal Illustrated: the equal distribution of average kinetic
energy in a gas at thermal equilibrium.

The Problem: A Big ball, a medium ball, and a little ball (colored red, yellow
and green respectively) are depicted bouncing around with a bunch of other
little balls (these balls are, of course, a representation of molecules in a
gas). The speed of each of the three colored balls is displayed in a separate
chart. The viewer is asked to decide which of the colored balls has the
greatest average kinetic energy.

Review: Very clever way to make the point: at equilibrium individual molecules
in a gas will have the same average kinetic energy. The only problem was
estimating the average speed from the wildly erratic speed vs. time chart.

Problem 5

I am admittedly confused by this problem. A container of gas decreases in
volume, while both the pressure and temperature remain constant. The viewer is
asked to calculate the work done on the gas. I can only assume that there is a
gaping hole somewhere in the container or that the thermometer, and/or the
pressure gauge is broken. The prospect of solving a problem dealing with a
non-closed system and/or erroneous measurements is somewhat more daunting than I
would care to face in a freshman physics class.

In conclusion I wouldsay that this site certainly has some educational merit,
but it by no means inspired me to trade in my freshman text books for a few
mega-bytes of Java source code.
Lawrence Sweet
Lawrence Sweet (Student)
21 years ago
The applet demonstrated how a material expands with four different heat
functions. The graphic demonstration is not really necessary--it takes less time
and energy to visualize different rates of expansion than it does to wait for
the applet to load on campus dual OS machines.

An excellent graphical demonstration of a sperical rising gas region. With the
data provided in the applet one can get started forming a model that provides a
solution technique. One thing left out, however, is a description of what the
fuzzy region around the gas sphere is and how it's effects are (possibly)
neglected in the model.

This animation of different kinematic gas models would be very illuminating to
one not familiar with the assumptions of the ideal gas law. The animations made
it apparent (well, we knew what was coming beforehand actually!) that the
correct model requires intermolecular spacing such that the molecules can be
considered non-interacting. It ran well on challenged hardware.

Quite an amazing simulation. A great demonstration about how mass is a factor in
the concept of kinetic energy. But, there needs to be a way to easily extract
data from the real time graph to work with the problem.

This applet appears to have a serious error in that the pressure does not change
in the animation as the volume drops and the temperature remains fixed.

Additional Problems:

A good applet to visualize the problem posed. All the extra numbers on the graph
are not needed, however.

Extremely slow running but very good applet that shows real time statistical
kinetics and how average molecular speed can be found from seemingly random
motion in a container.
Sheila Dodson
Sheila Dodson (Student)
21 years ago
This site was designed with an introductory college physics student in mind, and
yet that is particularly the audience it would do the greatest diservice! The
physics behind the problems are left vague and sometimes even misleading. This
would only leave a student more confused and bewildered about the world of
thermodynamics. The benefits of Java applets are far outweighed by the poor
design of this site. I have outlined the problems the page poses to it's
audience and a critique therof:

Re: problem 8.12.1:
It is extraordinarily difficult for a student to see the answer, stated so
obvioulsy, because not only are the Java scripts slow and inexact, but also
because the programmer chose to make the student view the rods expansion one at
a time, instead of simultaneously. As a result it would be virtually impossible
for the student to measure each rod's length and calculate for themselves the
conclusion, that all the rods are the same.
Re: Problem 8.12.2:
This Java applet is well-programmed, but the proceedure by which the author used
to arrive at his conclusions are not well spelled out, leaving the students to
wonder what assumptions were employed to reach his answer. I personally could
not find the route he took to reach the given answer of 13.6.
Re: Problem 8.12.3:
Unlike the previous two applets this one is surprizingly well done and
instructive in that it gives the students a chance to not only see the behavior
of an ideal gas in real time but it also gives them a chance to think
crittically about how an ideal gas would behave compared to other gases. My
only critticism is that again it is not obvious how the author reached the
conclusions he did, and the applet runs so slowly that it is difficult to see
how interacting (or non-interacting the molecules are)
Re: Problem 8.12.4:
This applet is well done, and poses and interesting question to the students.
It shows the motion of three different size molecules and their respectivespeeds and asks, " which has the greatest kinetic energy" and replys that all
three of them tie. I like the fact that the problem was enginered such that the
answer was not the obvious one, and makes the student realize that the kinetic
energy is not just a fuction of speed, but also of mass. I would reccomend that
instead of displaying the instantaneous velocity of the particles that instead
the applet would display the average velocity such that the student could
realistically make the calculations.
Re: Problem 8.12.5:
I believe there is something broken in this java applet. The animation implies
that a container is decreasing in volume, yet maintaining a constant pressure
and temperature! This cannot be, so it's not only impossible for the student to
arrive at the same answer, but it can be confusing to students who thought they
understood compression and work, and now they see this animation that breaks
all the rules!
Additional Problem one:
I enjoyed this applet, although it is VERY SLOW to run, and even slower after
making the reccomended changes. Despite the technical difficulties it is a
wonderful illustration of the relationship between pressure and temperature, and
a great reminder for early physics students about the meaning of equilibrium.
Additional Problem Two:
This last applet is instructive, but too difficult to use. The question
concerns a box of O2 molecules, where the individual speeds of the molecules are
given. It wants to know the average speed of all the molecules. I suggest
that instead of having to continuously average the speeds of the 20 molecules
over the course of 20 seconds, the applet be reduced to somthing like 5
molecules. By doing so it makes it feasible that a student could actually
average the speeds and arrive at an answer. Leave the mass computing to the
Chris Wolowiec
Chris Wolowiec (Student)
21 years ago
It appears as though this Thermodynamics physlet is directed at undergraduate
physics students who have had some education in classical thermodynamics. As an
upper division undergraduate physics student, I found approximately 90 minutes
to be sufficient time to work through the five problems presented in the
tutorial. Most of this time is spent deciphering the mechanics of the user
interface. That is, in answering the questions I found it generally difficult to
determine the spatial parameters required to answer the posed questions.

Problem 2 serves as a good example in illustrating this point: The problem asks
the user to find the ratio of two temperatures (final over initial) for an air
bubble that rises through a tank of water. The air bubble originates at some
distance below the surface of the water at which point an initial temperature
isdefined. The bubble expands in volume as it rises to the surface of the water
where it bursts. The final temperature of the air inside the bubble is defined
at the time immediately before the bubble bursts. In finding the ratio of the
final temperature to the initial temperature the student must recognize that the
gas is essentially ideal and that it undergoes
an expansion between the initial and final states. Some key insight is required
here. The user essentially has two choices for paradigm: isothermal expansion or
adiabatic expansion of an ideal gas. The isothermal expansion may be ruled out
as no heat is added to the gas as it expands and cools. Thus, the user may
decide on an adiabatic expansion paradigm and exploit the proper equations that
follow from the first law and the ideal gas approximation; namely that
(pressure)* (volume raised to the ratio of heat capacities) equals some
constant. From this relationship one may then express the ratio of temperatures
as a ratio of the respective pressure volume products at both the initial and
final states.This is where determining the proper
physical parameters becomes a little problematic. Namely, the user must
determine the initial and final volumes of the bubble. The volume of a sphere is
determined by its radius and so the user must somehow find the radius of the
bubble at both states. This is possible if the user places the cursor at various
points on the bubble to get the best
estimate. This might not seem too tricky except that there are no suggestions or
comments as to how to navigate through the animation. Some helpful comments
might be in order that would facilitate this process so as to allow the user to
spend less time on deciphering the interface and more time on the physics. This
may be taken as a matter of opinion as one might argue that part of the problem
solving here is figuring out how to get the information needed.

On this note, I'll comment that the other problems are less cryptic in that any
physical parameters or variables are much more easily determined. Problem 1, for
example, only requires the user to determine expansion distances for several
metal bars heated over some common time interval. These distances are easily
determined as the metal bars are superimposed over a grid calibrated in
centimeters. Thus, the user may easily draw some conclusion about the material
composition of the metal bars based on the average rates of thermal expansion
over some common time interval.

Problem 3 is a rather straightforward multiple choice question. The user is
presented with three different containers of gas. Of the three containers the
user is asked to select the container of gas particles that most closely
approximates the ideal gas. The particles vary in size and number from container
to container. All that?s required to answer this question correctly is a
working knowledge of what conditions are necessary for a gas to be considered

Problem 4 is another working knowledge type question that doesn ?t require any
calculations. The user is presented with graphics of four different types of
gas particles inside of a single container. The particles differ with respect to
mass. Adjacent to the container is a plot of each type of particles kinetic
energy vs. Time. The user then is asked to determine which of the particles has
the greatest average translational kinetic energy. The plot of kinetic energy
vs. Time, however is not really required to answer this question. If the user
remembers that average translational kinetic energy of a gas particle in a
container is proportional to temperature only and not mass, then he may arrive
at the correct answer. This particular presentation is a good example of a
problem that tests a users understanding of one of the more important
consequences of the kinetic theory of gases. In short it asks more of the
user?s understanding of physics and less of his ability to decipher the

Problem 5 is a bit more difficult than Problems 1,3, and 4. It requires some
calculations, specifically the use of integral calculus. The problem presents a
rather textbook isothermal compression of a gas. The graphics display a mass
on top of a piston. The user initiates the experiment and watches the piston do
work on the gas as the mass falls downward due to the force of gravity.
Throughout the experiment the user will notice thermometer measuring the
internal temperature of the gas to the left of the piston. It?s easy to see that
the temperature of the gas remains constant throughout the compression. Once
the user has determined the process is isothermal he may then find the work of
the gas by integrating the expression P*dV from the initial to final volumes. If
the user assumes the gas to be ideal he may find an expression for the pressure
in terms of volume from the ideal gas equation. Again some effort is needed in
deciphering the graphics in determining the these volumes but not as much as in
Problem 2.

In conclusion, this physlet might be best characterized as abrief homework
assignment testing the users understanding of the more basic concepts in
classical thermodynamics. Improvements could be made in the areas clarity in the
statement of the problems and graphics. In the area of graphics, it should be
mentioned that if the problem requires some insight into how to manipulate the
interface so as to acquire any necessary data/information, there should be some
suggestions as to how to get started. I think this can be done without giving
the problem away.