tt_icon_170This week’s episode of my Science Teaching Tips podcast actually features, well, me! Yay. It’s nice to record myself, not always other people, though the folks at the Exploratorium are so darned clever and fun, I feel it’s my mission to document every last scrap of their wisdom and energy. I’m trying…

So, this time I give you a way to adapt a great Exploratorium exhibit to something you can do at home with a friend and a set of keys.  It’s about how we localize sound, which is something very important for people who use sound to navigate (like blind people).  So, find out more about the perception of sound by listening in to this week’s episode.  For those of you who haven’t listened before, these are just 5 minutes long!

Listen to Find that Sound.


I’ve got so many different posts that I want to write… scribbled notes on different science myths and beautiful everyday things, but I have been so very busy. I’m sorry. I will get back to writing detailed posts in a few weeks!

In the meantime, I’d like to recycle a good old post on making your own phonograph. If you’ve got some old records, try this one, it’s pretty astounding when it works!


phonographI love this little activity… Have an old record but no record player? Here’s how you can listen to it. Take a record and stick a pencil through the hole in the middle so it’s pretty close to the point of the pencil. That’s your turntable. Now take a piece of paper and roll it up into a loose cone and tape it. Flatten the pointy end a little and stick a pin through it. You may want to tape the pin to the end of the paper cone so it’s more stable. Now have a friend turn the record by slowly rotating the pencil. Place the pin, point down, on the groove of the record, and gently hold the cone so the pin stays in the groove of the record. Try to turn it at 33 1/3 times per minute — good luck! Here is a more detailed description of the activity.

Here is my post on my podcast where you can hear how it sounds and how to teach it.

You should hear the music playing, albeit a bit wobbly. The record has a groove in it — one long spiral. The needle vibrates in response to the shape of the groove. But the needle on its own doesn’t vibrate very much air. When it’s attached to the cone, it vibrates the cone, which can then vibrate more air, making the sound louder. The cone also directs the sound, making it easier to hear.

Today’s students often haven’t seen a record before, and so it can be useful to look at it under a microscope or magnifying glass to see the groove. Note that a CD is also sort of “carved” — it has microscopic pits in it. But instead of mechanical vibrations, the grooves in the CD are so tiny that it interacts with light. That’s why records wear out — the needle wears out the grooves. That’s not a problem with CD’s, since it’s just light touching the surface. Interestingly, it doesn’t matter (as much) if you scratch the side of the CD with the rainbows on it — but if you scratch the metal coating on the other side, the light won’t reflect from it correctly and you’ll spoil the CD.

Wikipedia has more information on phonographs, and so does this site from Arbor Scientific.

If you’re interested in making your own working phonograph (not just the pin and paper method) to actually record your voice using a plastic cup (replacing the old fashioned wax cylinder), check out this kit from Make Magazine. I hear they don’t carry the kit anymore, but someone Googled and found it by a company in Japan.

Here’s a video of it in action and here’s what it sounds like.

A teacher on a teacher listserv I’m on writes:

In my collection of Edison Phonographs I have many that will allow for purely mechanical reproduction of sound. I have an Edison tinfoil phonograph that records on tinfoil (duh) and numerous machines that record on wax cylinders. First the wax cylinder is shaved to a clean surface then a cutter head consisting of a diaphragm with a sapphire cutting stylus is lowered onto the record surface. As the cylinder turns, wax is cut by the stylus where the depth of the cut represents the wave pushing/pulling on the diaphragm. It is called the “hill and dale” or vertical cut type of recording.

The Gakken phonograph made in Japan uses a side by side motion or lateral recording. This is what the common 78 RPM records used from 1896 up through the mid-1950s. The toy phonograph does work but results vary depending on numerous factors. One is the temperature of the plastic cup used for the recording. I have found that a hair dryer warming the cup helps but one must be careful not to melt anything. The Gakken machine appears on eBay regularly under the search Edison Phonograph but shipping is as expensive as the machine is because it is air mailed from Japan. Maker Shed in the US carries it as well with some savings on postage but at a higher price.

What is it that makes your ears ring after something loud (like a private iPod concert turned up too high)? The highfalutin’ word for it is “tinnitus.” When your ear is exposed to sounds that are too loud, the hair cells in the inner ear that act as little sound sensors get damaged. In response to the damage, the brain “turns up the volume” as part of a feedback mechanism. That “increased gain” is what you hear as ringing. After a while the ringing goes away, because you get used to it, but the damage has still been done. So, ringing in your ears is a symptom that you’ve damaged your hearing.

I also had really strong tinnitus when I was on quinine after I contracted malaria — not a sign of hearing loss but just a side effect of the drug. It was so bad that my mother had to shout for me to hear her!

When you’re young, you’ve got lots of excess hair cells that compensate for the loss of the damaged ones. But as we get older, and lose hair cells through the natural process of aging, those of us with a lot of damaged hair cells don’t have any to replace those lost as we age. So we don’t notice the effects of those loud rock concerts until many years later. Isn’t that just the way with so many health problems? By age 25, the average carpenter has the hearing of a 50-year old. Wear your ear protection!

Another thing that happens as we age is that we don’t hear high frequencies as well — a factoid that has been made pretty well known by the new trend of young people having cell phones with high-pitched rings that adults can’t hear. I was in the audience once for a pretty neat demonstration of this effect. It was a physics show, with people ranging from 8 to 60 years old. The professor played an extremely high pitched sound that nobody could hear, and asked us to raise our hands when we heard it. He began to lower the frequency. All the kids’ hands shot up pretty quick, but us old farts had to wait until the sound got much lower before raising our hands. I was disturbed to see that my hand was one of the last up (and I’m not that old!).

Paul plays the whirly - From

Paul plays the whirly - From

Us geeks have strange hobbies. My old boss, Paul D., plays the corrugated plastic tube, also known as a “whirly.” I just posted a new episode of my Science Teaching Tips podcast where he plays the whirly (like a true master) and explains the science behind the sound. It’s not quite what you might think! I was surprised. I figured, as do most people, that it’s air moving across the top of the whirly, like blowing across the top of a soda bottle. It’s not.

Listen to the episode – Whirled Music.

From Paul’s website:

While playing the whirly:
1. Cover the stationary end with your hand. Notice that the sound stops immediately.
2. Hold the stationary end near the burning candle, notice that the flame bends into the whirly.
3. Hold the stationary end of the whirly near a pile of confetti, or other small paper pieces. For the best effect hold the confetti in a strainer so that air can flow around the confetti. Notice that when the whirly is signing a note the paper pieces flow into the whirly and are sprayed around.

Notice that, when the whirly sings, air flows through the tube.

What’s Going On?

Why does air flow through a whirly?
Picture a whirly full of marbles. If you twirled such a whirly, the marbles would fly out of the spinning end. This is what happens to the air in the whirly. The faster you spin the whirly the faster the marbles and the air will flow through it. The wall of the whirly moves in a circle, to make the air inside the whirly move in a circle a centripetal force is needed. The whirly is open at the end so in the absence of centripetal force the air inside the whirly accelerates along the rotating tube. Air flows through the rotating whirly.

One way to say this is that “You throw the air out of the whirly.”

More about the science of whirlies on Paul’s website here and here.

And see a video on Steve Spangler Science here.

TI staff educator Eric Muller explains how to make your own record player!

I just posted a new episode of my Science Teaching Tips podcast.  Exploratorium staff physicist Thomas Humphrey divulges a clever way to measure the speed of sound, and he explains how he’s used that information to measure things in the world.

I just read this neat little gem in The Physics Teacher. Take a bunch of coffee stirrers (the kind that look like round straws for wee folke) and set them into a box so they’re all upright (all the little holes are looking up at you). Jiggle them and pack them tightly so that they seal flat against the side of the box with no “holes”. Then go somewhere that has a lot of loud ambient noise (I’m imagining the Exploratorium on a busy day), and put the open end of the straws against your ear.

According to The Weird Project, you’ll feel as if:

  • the air pressure is falling
  • invisible pillows are drifting around your head
  • your ears are about to pop
  • you are going deaf
  • your head is changing size
  • the size of the room is shrinking
  • you are about to faint
  • In other words, what happens is that part of the background sound goes away. Apparently when it works right, the effect is “very creepy.”

    What happens is that certain frequency bands (eg., certain pitches of sound) are attenuated (read, “partially blocked”) by the straws. The article in the Physics Teacher describes how to use a function generator and a speaker to determine which set of frequencies are most affected. They found that for 13.3 cm round stirrers, the sound level drops off at 660 Hz (I think that’s a high “A”) and again at 2000-3200 Hz. You can get a rough idea for the pitches of those sounds here.

    If you’re curious about this, definitely check out The Weird Project, it’s got a lot of good information on it.