On Tuesday afternoon (8/6/13) in E1, the class activity was
to identify all forms of energy that were present in the morning example of a
puck being flung across the floor by a bent back meter stick, as well as state
evidence for each type of energy. A
third category was created, called the micro-story, in order to describe what
action is occurring at the microscopic level.
This micro-story category was introduced because the class was realizing
that both the moving object (puck) and sound were forms of kinetic energy. They did not point out that thermal energy was
also a type of kinetic, but that would have further necessitated this new
category.
To fully describe the micro-story, the class was asked to
gather at the center of the room and act out each type of energy. They went through thermal and wind first, as
examples. Right before this episode
begins, they are setting up for performing sound energy. They decided to form two lines (in hindsight,
I’m not sure why they formed TWO lines; maybe because one line would not fit in
the room?) As the video begins, they are
trying to determine what the particle motion will look like.
The full line pushes to the right to begin with, each person
being “hip-checked.” Barbara asks at
0:14, “Then you go back, right?”
Comments follow, such as “sound bounced off the wall” and “yeah, there
was an echo.” So initial thoughts seem
to center on reflection, where a particle moves only when bumped by another
one, whether coming from the left or right.
Lane draws them further into this idea, stating back to them
what they are saying at 0:27. “I know
that when you bumped me, I was supposed to move this way.” Barbara, on the right track, says “and then
you go back.” Which is the comment she
made at 0:14. Mike and John, at 0:40,
jump in with their competing model.
Specifically, John describes sound as a Newton’s Cradle. This seems to be a very compelling argument
for many in the group at 0:47, including Barbara.
Cynthia is troubled by this, though. She softly asks “So how do we know it’s like
a Newton’s Cradle” at 1:01. She gets
everyone’s attention at 1:15 and loudly asks this question.
I love this conversation because two competing models of
sound present themselves. One is a
linear model, the Newton’s Cradle model, where a particle of air will only move
when bumped from one side. The other
model I’ll call the Slinky model, where a particle will go back to its original
position, regardless of echoes. In fact,
if you continue to watch the full video, Trevor retrieves a slinky from the
class supplies and demonstrates wave pulses.
Both of these are compelling models, but neither of them at this point
is backed by true evidence. I think
people are buying into the slinky model because they “know” sound is a wave and
that the slinky represents waves.
After the slinky demonstration, Cynthia repeats her
question. She knows she has not received
actual evidence; merely a nice demonstrative model. Finally, some examples are suggested. The second episode shown here begins with
Cynthia asking her question and ending with Trevor describing a high-speed,
slow-motion video of water flowing from a garden hose beside a speaker. I do not find the dialog itself in this video
particularly enlightening, but I include it for completeness. It was fortunate that his class included a
skeptic that demanded evidence, and it was fortunate that there WAS
evidence. (Actually, the video was not
shown, so technically no evidence was given.)
I feel these videos may be a good reminder to train our students to be
skeptics and then to always have the proper evidence ready to be presented.
Full video: E1 130806 1253 T6-1
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