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8.12.1 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.
8.12.2 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.
8.12.3 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.
8.12.4 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.
8.12.5 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.
12 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 site.
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.
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.
12 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 computers!
12 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 ideal.
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 interface.
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.
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.
12 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 containers. 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 shown? 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?
12 years ago
[8.12.1]: 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.
[8.12.2]: 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.
[8.12.3]: 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.
[8.12.4]: 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.
[8.12.5]: 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.
1: A good applet to visualize the problem posed. All the extra numbers on the graph are not needed, however.
2: 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.