Classroom Activities


tt_icon_170In this week’s episode of Science Teaching Tips, we look at my favorite thing — light.  Light, like, rulez.  Dude.  And so does my old mentor, Paul Doherty, who will tell you one of his best stories from the history of science about how the spectrum came to be the spectrum.  I mean, what the heck is indigo anyway?  The answer turns out to be, like all good history of science stories, steeped in mysticism and superstition.   Give it a listen, it’s a good story!

Episode 65:  Revising the Rainbow.

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I’m surprised at the number of people who haven’t seen this one, but then again, neither had I until I went to the Exploratorium (where they’ll stick anything in a microwave).

Put a bar of Ivory Soap (no substitutes!) on a paper towel in the middle of the microwave.  Press go.  About 2 minutes should do it.  Here’s what happens:

And this video will show you what it looks like when you take it out afterwards

What’s going on?  Well, the reason that Ivory Soap floats (try it) is that it’s puffed full of air (here’s some history of why that is).  There are tons of tiny bubbles whipped into it, sort of like when you make whipped cream.  It’s an emulsion of soap and air.  The bubbles of air have water vapor in it.  When you microwave it, that water vapor creates pressure on the air bubbles making them expand and puff up.  The air bubbles themselves expand as they heat since the volume of a gas increases with temperature (Charles’ Law).  And the soap softens, which allows the whole thing to expand into a big puffy pile.  And when you stop heating it?  The soap’s no longer soft, so it gets rigid and hard, but stays its expanded puffy self.  You can use it like soap now, though it’ll be a little weird!

Other brands of soap tend to just melt.

Here’s a nice explanation, as well as how to use this as a classroom lesson on density, from Steve Spangler Science.  And some more classroom suggestions from About.com.

Here are some great gems from some really old posts over at Swans on Tea. Thanks to Rhett at DotPhysics for the technical assistance.

Robots doing amazing things:

Carbon dioxide is heavier than air (neat thing to try at home)

Weird psychology trick (how does he do that?)

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!

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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.

tt_icon_170Have you ever really listened to the sound of a bouncing ball? There’s some elegant mathematics to be had in this simple thing. In this episode of my Science Teaching Tips podcast, staff educator and physicist Tom Humphrey takes us to the most perfect bouncing ball I’ve ever seen (or heard) — an exhibit at the Exploratorium. The platform the ball is bouncing on is a huge chunk of heavy marble, bolted to the floor. (What does that have to do with anything? Think about conservation of energy and momentum). You hear some surprising things as a small metal ball bounces on that surface. Even without the exhibit, this is something you can do with your students, and integrate science and math into your curriculum.

Listen to the episode – Follow the bouncing ball

tt_icon_170Despite my better judgment, I invite TI staff educator Eric Muller to do one more set of activities on my Teaching Tips podcast —several things you can do with soda straws.  Listen to the episode – The Last Straw.


Holding Charge activity (PDF)
More of Eric Muller’s activities

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