[Elecraft] Third grade science report: Physics of Sound

[Leigh L Klotz, Jr.]

I am presenting a 2 hour adjunct to the "Physics of Sound" science unit 
for the 3rd grade at my local elementary school here in Palo Alto, CA.  
I have recently finished the unit with one classroom, and it went quite 
well.  Below is the report of the first class, with which I did one hour 
units each on "Time and Frequency Domain Analysis" and "Communicating 
with Sound (but without speech)" presented one week apart.

I have a copy of the syllabus I developed (sketchy though it is) at 
http://wa5znu.org/2006/11/sound and it includes a link to the take-home 
sheet I made showing where to get the PC software for home experiments.

The first hour was on time and frequency domain, and I appeared at the 
appointed hour in a lab coat with the name label "Joey" sewn on.  
(Thanks Joey!) I brought a half-yardstick and marker, an HP audio 
oscillator, speaker, microphone, laptop with free PC oscilloscope 
program, a stringed instrument, a microphone, a toy piano, and an AM 
radio.

As I set up the laptop and projector, the teacher talked about pitch and 
loudness, a subject previously discussed.  Once set up, I asked the 
class to demonstrate 3 of the 4 attributes (high, low, soft) and asked 
for ideas about why I wouldn't ask a 3rd grade class to demonstrate 
"loud."

I explained cycles and seconds and connected Hz to other units they had 
studied (degrees, centimeters, inches) through questions to the class, 
and asked for the range of hearing, and eventually arrived at the 
standard answer.  I then demonstrated a 1KHz tone and we wrote down a 
few guesses, but I didn't disclose the answer.  I showed the oscillator 
and explained a brief version of the HP founding story (it was started 
and is still here in Palo Alto: only one kid's parent worked at HP; I 
had expected more).

I got a few volunteers help make a mechanical oscilloscope...we taped a 
marker to the end of a yardstick (I used an 18" one) and set it to 
oscillate while another kid pulled a sheet of flip-chart paper, and the 
class timed it.  We all observed the sine waves (a bit distorted) and 
many kids gasped as they saw the same shape they'd seen in the diagrams 
they'd been shown before in class.  We then counted the cycles (9) and 
divided by the time in seconds (6) to ger 1.5Hz.  About 5 kids could do 
this division, and I had previously related unit division to 
miles-per-hour.  One kid suggested if we shortened the stick it would go 
faster.

Then I showed the PC scope and the oscillator with the 1KHz tone, and 
adjusted both the frequency and amplitude controls up and down, showing 
this all in the time domain.  With an older class, I might have done the 
division at this point, but in order to make the concepts more 
accessible, I told them we could use the computer to do the frequency 
calculation for us, and switched to a power spectrum (FFT) display, 
which showed a nice sharp peak at 1000 Hz.  We then compared their 
answers, which had been in the 2000-6000Hz range.  We discussed the 
range of hearing of children, adults, people, dogs, and bats.

I told them that volume, although we wouldn't be exploring it, was 
measured in deciBels, and the teacher wrote it on the board and 
underlined the metric prefix, to tie it into a previous unit on 
measurement.

We tried the various instruments, and multiple sounds to see multiple 
peaks.  I pointed out the 1KHz peak among the noise of 20 kids talking, 
and showed them a chart of the cochlea and likened its spiral to the 
power spectrum X axis, and said that roughly speaking that is why they 
can hear both the tone and the noise at the same time.  I asked if 
anyone ever had sudden ringing in the ears and said that some doctors 
think it is caused by a single hair cell in the ear.  I pointed out the 
height of tone above the noise, implicitly demonstrating s/n ratio.

We then tried pitch matching and saw that the voice contains multiple 
frequencies, and that the stringed instrument had strong 3rd harmonics, 
whose values they calculated.  This led to a discussion of octaves, as 
about a third of the class took piano.  (I wanted to get into other 
intervals and ratios but there wasn't time.)

We did some matching of the oscillator to the tones of the instruments 
and voices, and closed with a review of pitch and volume with the 
oscillator on both the time and frequency displays.  There was a lot of 
demand for higher and higher frequencies (mostly from the boys, for some 
reason), so next time I'll try to find a higher fidelity speaker.  But I 
did demonstrate leaving the audio range, and went up the 1 MHz, where I 
showed the electrical waves now being called radio waves, and picked up 
the scratch signal on an AM broadcast band radio at 1MHz.

By the end of the hour, the kids could answer questions about 
measurement of frequency, knew the range of hearing and could estimate 
the frequency of an audio tone,  knew what Hz was, and had a few ideas 
for experiments to do at home (no PC required).

For the second week, I brought two laptops loaded with the PC version of 
PocketDigi (a very uncluttered digimode program available at 
http://pocketdigi.sourceforge.net) an external mic, and a CW practice 
set, composed of the ARRL No-Solder oscillator and the IOWA QRP key.  
(These last two are appropriate level science fair projects for 
elementary kids.)

I asked for some ways that we could communicate with sound but without 
talking, and we discussed speech acquisition by babies (or is it cry 
recognition acquisition by parents ;) and a few other ideas.  One kid 
suggested morse code, so I brought out the key and showed them the 
PocketDigi waterfall display (note to self: ask Vojtech for a 
right-to-left scroll option), but we didn't get into CW at that point.

I briefly showed a PSK31 idle signal in both time and frequency domain , 
and quickly explained that when computers communicate with each other, 
whether it is the Internet at home or over a telephone dialup, or 
through air like we were doing, they always do it with waves, and that 
these waves were one way of doing that communications.  I then typed on 
one keyboard and they saw the signal on the waterfall and the text 
appear, and we tested how far we could get before the signal faded into 
the noise and the recognition stopped.  They had fun reading the text 
messages I typed.

Then we segued to Morse code; one kid had studied it at a cub scout 
troop (bless them) but didn't remember it.  Rather than doing a long 
explanation of morse code, I said that I would now demonstrate how to 
communicate by sound without talking, just by using my ears (and 
cochlea) instead of the computer program.  Fortunately, I had a 
confederate planted in the class who could send CW reliably.(Sorry if 
this part is like like those recipes in the newspaper that say "Now 
ladle on the sauce, which you should have prepared in early spring...")

I treated this demonstration like a magic trick, and with just a hint of 
explanation, turned my back, covered my eyes, and asked my trusty 
assistant to pick kids who had raised their hand (all of them did, of 
course) and send their names, and I would figure out who each was.  My 
pronouncements of RENEE and EMMA and ANDREW were greeted with as much 
excitement as if I had pulled a live guinea pig out of my hat.  JOLLY 
though produced quite a bit of laughter, though, and we ended the 
demonstration and switched back to discussion with an explanation of how 
someone could confuse H and J.

By this time, the class was ready for some information and discussion, 
and I wrote down (though cautioned that it's not he way to learn the 
sounds) E I S H A N T M and asked for opinions along the way about why 
the letters were different length.  I mentioned a bit of the Alfred Vail 
controversy to get them to cheer for the underdog assistant, and asked 
for ideas about how to determine letter frequency.  After a bit of 
discussion on this topic, I suggested that they all try making a letter 
frequency chart of a page or two of their favorite book and see how it 
worked out.  Intermixed was a bit more demonstration of sending the 
high-point Scrabble letters Q, X, J, and Z, and a note that all numbers 
are 5 elements and punctuation 6 (shown with period).  A few other free 
discussion topics came up as well, in response to questions, and I 
mentioned the Jay Leno (K7JA/K6CTW) results.

I picked a three-letter word and asked the class to call out the letters 
as I spoke them (di-di-dit dit dit), and right afterwards was quite 
surprised when a girl who spoke halting English asked to come up to the 
board.  She wrote down something in dits and dahs and asked the class to 
decipher it; she had written EINSTEIN.

We went back to discussing frequency and I wrote down the metric 
prefixes going through KHz, MHz, GHz, and THz.  (I made a mistake on the 
numerical value of THz and akid corrected me!).  We discussed familar 
examples of each (sound, radio, computer speeds) and then for THz, I 
told them about the frequency of light.  I then switched to showing 
sound waves modulating light, using a fiber optic experiment kit (about 
$20).  I went around the class showing the light going through the 1m 
optical fiber, and used my finger to start and stop it in a tacit 
demonstration of CW modulation.   Back at the demo table, I turned on 
the tone generator in the experiment kit and showed sending CW over 
light; several kids were sure it was a wire, so I pulled it out and 
aimed the IR parts at each other; we saw how the sound transmitted over 
light through air, and I explained that the frequency of the light was 
something on the order of 300 THz.

It was then time for recess, and though I had brought my KX1 with the 
intent of letting them listen to people "communicating with sound" over 
the radio, there was no time.  So I left the teacher with 21 copies of 
the handout sheet to be sent home.  On the way out the door, the girl 
who wrote EINSTEIN stopped by and asked me please for a Morse code 
chart.

The next week, the class had a test on sound and frequency, and reports 
were that the two hours had really made the ideas "come alive" for the 
students, and the classroom newsletter reported that the Morse code 
demonstration was the big hit of the week.

73,
Leigh/WA5ZNU