I have used VideoGraph (a MAC product, available through Physics Academic
Software) with my HS physics students for two years.
The projectile motion anaysis is superior to almost any other approach I
have used (Interactive Physics simulations are more versatile, but they
are, of course, simulations). I have had students analyze momentum
conservation and kinetic energy changes in 2D collisions on an air table
(next time I will try some sort of midair collision). I have also had
them study the propagation of waves in springs (a first attempt that I
will not repeat).
To discuss pros and cons, I will mention two uses from this year's class:
First, I had them do the traditional air-track force, mass, and
acceleration lab (which I, as a student, did using Polaroid photography
with a strobe). Because we had to load the video clips for nine separate
trials, all students operated from the same videotape. Therefore, they
were not all active participants in the making of the video clips. I had
to download the clips into computer files and then copy the files onto
floppies for the students to use in the computer lab. That was
time-consuming and required video compression software.
The positives:
1. students were able to analyze and replay motion events in a format
that they are familiar and comfortable with (video),
2. the students had to problem-solve how to determine the acceleration
from the VideoGraph data displays (even though the program displays
acceleration plots, they found the most consistent results by finding the
slope of the velocity plots),
3. students who erred in their analysis could go back to the videos and
start over, and
4. due to the inherent inaccuracies of marking the position of the
glider on the small, grainy, videoclip, the students had to confront the
concept of measurement "error" yet were still able to determine trends.
The negatives:
1. the lack of active participation by all in performing the experiment,
2. the poor quality of the videoclips that result from the process of
grabbing individual fields -- [BACKGROUND: Two fields are interleaved to
make a frame. Since our camcorder takes 30 frames per second, it
actually takes 60 fields per second. Each field has half the resolution
of a frame. When you "freeze-frame" on a regular videotape, you are
actually seeing two fields super-imposed on each other. Obviously, video
analysis of motion requires looking at fields rather than frames (since
the moving object has changed position between the recording of the first
field to the second field). Therefore, the video clips have half the
resolution that you might expect],
3. the inexplicable inability of VideoGraph to provide data tables of
velocity and acceleration (it does provide a data table of position but,
even though it plots velocity and acceleration graphs, no data tables are
made available), and
4. a bug that causes the printout of the position data to differ from
the display we saw on the screen (I surmise that the data readout on the
screen is calibrated and the data sent to the printer is the uncalibrated
raw data).
Later in the year, when we did independent research projects, several
students chose to use video analysis. Students were able to analyze
events of very short duration, about 1/10 second. There were obstacles
for them to overcome in their analyses, but I saw that as a positive
development. These students copied the data from VideoGraph and used
more sophisticated graphical anaysis programs. The students became adept
at making and downloading the clips (which they had to do several times
because I kept my mouth shut and let them make obvious errors like not
including a calibration standard in the frame).
Bottom Line: Don't expect saving time with lab exercises (it takes
longer than alternative paths). Don't expect improved accuracy. Do
expect that students will "take to" video analysis with relative ease
(tho' some take longer than others to become comfortable). Do expect
that your students will be able to analyze some motions that were
previously unaccessible (but the poor image quality hampers "wide angle"
motion).
Dave
David J. Hamilton, Ed.D. "And gladly wolde he lerne,
Franklin HS, Portland, OR and gladly teche."
djhamil@teleport.com Geoffrey Chaucer