Back to comment hit list
Back to comment hit list
Search all MERLOT
Click here to go to your profile
Select to go to your workspace
Click here to go to your Dashboard Report
Click here to go to your Content Builder
Click here to log out
Search Terms
Enter username
Enter password
Please give at least one keyword of at least three characters for the search to work with. The more keywords you give, the better the search will work for you.
select OK to launch help window
cancel help

MERLOT II


    

Comment


Material:

Physlet Problems: Thermodynamics

Rating: 2 stars
Used in Course: Not used in course
Submitted by: Ian Clark (Student), Mar 27, 2001
Comment: 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.


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.