Written in Fire

We split Friday morning into two unrelated activities: sound, and a
review of states of matter.

For sound, I brought a lot of toys: tuning forks, a xylophone, etc.
The standard I wanted to cover was "sound is made by vibrating objects
and can be described by its pitch and volume" so I started with the
tuning forks and steered a discussion of pitch and volume (they
noticed right away that the tuning fork vibrated).  It was pretty
funny, as the kids focused entirely on pitch, and I could not get them
to guess, despite numerous hints, that VOLUME or LOUDNESS was a
difference between the two sounds I was playing, even when they were
the same pitch.  (It didn't help that when I really whacked the
xylophone hard, it did change its pitch somewhat as the whole thing
shook.)

Then I turned the kids loose to play with the tuning forks, the
xylophone, and a few other toys:

• bathtub flutes, which you can fill with water and then blow on while they drain.  The pitch corresponds (inversely) to the length of the wave which just fits in the air-filled part of the tube, so the pitch starts out high and then drops as the water level drops.

• plastic hoses flared on one end.  You whirl them around quickly, and they make an eerie whistling noise.  Same principle as the flute, only this time the length is fixed, and we make the air flow by whirling the tube rather than blowing on it.

• a "thunder stick" which is a long spring connected to a drum membrane stretched over one end of a tube (the other end is open).  Holding the tube and shaking it results in surprisingly loud boingy sounds.

Then we got back together as a group and talked about how our
observations are explained by sound being a wave.  To visualize this,
Teacher Pa and I stretched a very long spring (like the coiled wire
that ran from a telephone to its handset, in the old days before
wireless phones) across the room, and I bunched up my end and released
the bunch (still holding my end).  It was very clear that a pulse
traveled the length of the spring to Teacher Pa, and it bounced off
her and came back to me.  I related this to the behavior of the
thunder stick (what do you think happens if you hold the spring rather
than the tube?)  We also had two plastic cups linked by a string, and
Teacher Pa gave a chance for each kid to hear her voice carried along
by the string.

For the piece de resistance I brought a Rubens tube.  This is a long
tube with many small holes drilled in a line, connected to a propane
tank.  You turn the propane on and light the holes so it looks like a
row of 100 candles.  Now comes the cool part: there is a speaker
attached to one one.  Hooking it up so that music plays on the speaker
makes waves in the propane in the tube and pushes it out more in some
places than in others.  The fire dances to the music!  Music has lots
of tones mixed together though, so it's best to start with some pure
tones.  I brought a function generator to generate tones of any
desired frequency and amplitude, which is a really great
visualization.  Into and beyond break/snack time, kids and teachers
from all the rooms in the school were cycling through our room and
watching this.  The upper graders were transfixed.  They wanted to try
all their favorite songs.  We found that (to the dismay of some)
Gangnam Style was a really good one for making the flames dance.  We
eventually had to shut it down at close to 11:30, about an hour after
I first fired it up.  To see a Rubens tube in action yourself, check out this educational video.

From 11:30 to 12:15, Teacher Pa led us through some activities
reviewing the states of matter.  For example, she passed out images of
many different things and the kids had to paste them onto a poster in
the Solid column, the Liquid Column, or the Gas column.  This was
really useful for the kids, and for the teachers to assess how much
the kids got it.  In discussing this with the kids, we found a great
idea for next week: clarifying what we mean by "amount" or "size" of
something.  The difference between "size" (which most people would
take to mean a diameter, a distance across, or a height) and volume
came up in the context of gas expanding to fill its container, and it
was clear that we didn't have time to address it that day.  So we'll
do that next time.  It will play into one of the Investigation and
Experimentation standards about measuring length and volume, but I
want to keep it conceptually rich as I did last year.