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.

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

Needing to teach Newton’s Laws?  Don Rathjen, staff educator at the Exploratorium, has been teaching mechanics to students for over 20 years.  This one’s an old favorite — a noisy activity with wood flying everywhere.  You can listen to Don demonstrate how to teach the activity (and geekgirl has some fun with it too) on my Science Teaching Tips podcast.

Here’s a PDF of the activity, and the related Old Tablecloth Trick.

From the activity writeup:

The key concept here is inertia, or resistance to change in motion.  Mass is a measure
of inertia, as shown in Newton’s Second Law, F=ma; for a given force, the larger the
mass, the smaller the acceleration, or change in motion. The “whack” force applied to
the bottom block is far larger than the opposing friction forces from the table and
the remaining block stack, so the bottom cassette undergoes a large acceleration.
Because of the frictional force between the bottom block and block stack
above it, the stack accelerates as well; but the force is small and only occurs for a
very short period of time, and therefore doesn’t give the relatively massive stack much
acceleration before the bottom block is gone. So the stack just drops. Notice as the
blocks are knocked from the stack, the top stack moves farther. Since the stack has
less mass, it has less inertia.

More of Don’s activities here.

A fabulous science activity from Sebastien Martin over at the Exploratorium, via teacher Bree Barnett — visualizing kinetics with LED lights. See detailed instructions and more pictures over at that blog post.

A teacher asked for a good experiment to show 8th graders that gas has mass.  “We have used balloons in the past,” she says, “but some of the kids still don’t make the connection.”

Paul Doherty replied:

I like to get a big weather balloon from a surplus store , inflate it until it is 1 meter in diameter or a little more and then a second balloon that is deflated.

Have a kid stand and throw the empty balloon at the back of their head…they feel almost no force.

Then throw the full one. It packs a noticeable punch due to the mass of moving air. the mass approaches a kilogram.

Of course you cannot weigh it using a scale due to buoyancy. You can only feel the mass by accelerating it or decelerating it.

And Eric Muller added:

Get some dry ice. It is solid Carbon Dioxide and it has noticeable mass. Lots of stores around the bay area sell dry ice. Many Safeways, Albertsons, bait shops, liquor stores, ice distributors and welding supply companies carry dry ice.

Weigh (or Mass) a chunk of dry ice. Put the chunk in a plastic bag and tie it off. It will sublimate and turn into a gas. The bag will expand noticeable. A solid, 44gram chunk of dry ice (that’s the size of a couple of fingers) will expand to around 22.4 liters of gas.

Gas has mass!

I posted a new podcast – “Ooh you make my motor run” on my Science Teaching Tips podcast.  One of the Exploratorium staff educators, Modesto Tamez, tells how he gets students exploring electromagnets, a great preparation for making an electric motor.

Here’s the Stripped Down Motor activity: www.exploratorium.edu/snacks/stripped_down_motor.html

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

[[AAPT Session: Study of Computer Simulations — Interface design for engagement, learning and assessment, Wendy Adams]]

You know, when I first arrived at the University of Colorado, everyone was talking about these PhET Simulations that showed virtual versions of real physics phenomena, and I was really skeptical. Why simulate physics when you can go out and touch it, in real life? That’s much more engaging.

But, I have to say, I’m a convert. Teachers rave about them. Wendy Adams from our group gave a great talk about the simulations, how they’re effective, and some of the research on how they can best be used.

What the simulations offer over, say, an introductory lab using real equipment, is:

  • They can make the invisible (like electrons) visible
  • They’re interactive and animated, and quite realistically simulate real equipment
  • You can see the same situation several different ways (“multiple representations”), such as the real-world view, look inside it (to see the electrons), graph certain values (like the potential energy), see electric field meters, etc.
  • They don’t need to be as carefully guided as a real lab
  • They’re really fun and engaging.

There has been some encouraging research on the effectiveness on the simulations (see that work here). For example, one study gave half of an introductory class a simulation on circuits, and half used the regular introductory lab. Then, all students had to use the real lab equipment. They found that students who had used the simulation not only did better on the final exam, but they were also better able to use the real equipment!

They also found that:

  • With the real equipment, the TA can’t keep up with the multitude of questions and problems that crop up in lab. That’s not a problem with the simulations.
  • Students are nervous about getting electrocuted or damaging the equipment with the real lab, but with the simulation they can try a lot of different configurations and discuss it without that fear.
  • With the real equpment, students try to get a single answer from the lab setup, which is challenging because of all the problems with the equipment. If they don’t get the answer they expect, they suspect a problem with the equipment. In the simulation, when they see something different than they expect, then they think about the physics and their understanding, since they don’t suspect a problem with the simulation.

They also found that students did best with the simulations with minimal guidance. When given really direct questions like, “what does this slider do,” then they don’t go beyond the bounds of that question, they don’t tie the pieces together. If you don’t ask about a particular aspect of the simulation, then they totally miss it. But if you give no guidance, or very open questions like “how many ways can you light the lightbulb” then they fully explore the simulation until they understand it.

If you haven’t seen the simulations, then check them out! They’ve got ones for physics, math, and some others like geology.

I just realized that the PIE institute has a wonderful website! PIE is “Playful Invention and Exploration” – or integrating engineering with artistic expression. Their web page is a treasure chest for any maker… let me tell you (especially those of you who like to hack and Make and all that), it’s a delightful creative world of science fun. PIE is a little self-funded institute in the Exploratorium run by two PI’s, Karen and Mike. Since it’s got its own grant-funding, they can go off and do the kind of creative play that got the Exploratorium its name, generally using techie kind of stuff (and they also have a predilection for music). It grew out of a program from the MIT Media Lab. They show up at the Maker Faire, so be sure to check them out if you’re in the Bay Area. Here are some videos from their workshops.

To give you a taste, at one of the Exploratorium parties Karen and Mike laid out a little electronically wired mat, connected to a music synthesizer. The catch — the circuit was incomplete. The only way to make music was to stand on the mat with someone else, and hold hands. (Sweaty hands worked best).

Their website gives instructions for making beautiful light paintings with a digital camera, cardboard automata, and singing stones.

Sorry for the long delay in posting (not that it matters — I see my stats — most of you are off reading my old posts about how water goes around drains or whether polar bear fur is fiber optic). I’ve been on vacation back in my old haunts in the SF Bay Area, and thought that I would have lots of time to post, but I was too busy enjoying myself.

While I was back, I stopped through my old alma mater — the Exploratorium — and watched Paul Doherty teaching about light. You might know the old trick of using a diffraction grating to see the rainbow. You put a diffraction grating over a bright light (an overhead projector works great) and you see white light projected on the wall. Next you block off most of the light except for a narrow slit (you can cut a manilla folder to do this). You’ll see a rainbow (blue, green, red) projected on the wall on either side of the slit. What’s going on? Light bends around the tiny slits in the diffraction grating (red bends more), making infinite numbers of overlapping rainbows, which we see as white light. The slit blocks out all the rainbows that are there except for one, so we can see a clear blue/green/red pattern. (Think about that a moment, it’s a subtle point, and important).

The tiny grooves in a CD act like a diffraction grating too, that’s why they look rainbow colored.

However, it gets really interesting. Now, take away the “slit” so we just see white light again. Put an “antislit” in front of the grating… basically, a long thin strip of paper the same size and shape as the “slit” was. Instead of letting in a narrow strip of light, we’re blocking all but a narrow strip of light.

Instead of a rainbow to either side of the antislit, we now see the *complement* of the rainbow — yellow, magenta, cyan. Why is *that*?

Think about it.

WIthout the “antislit” there, you have white light, an infinite number of overlapping rainbows.

When you put the antislit there, you have blocked a “slit” — blocking the rainbow pattern that you saw with the slit there.

So what you see is “white minus blue” which is yellow, plus “white minus green” which is magenta, and “white minus red” which is cyan.

This is similar to Bob Mlller’s wonderful light walk, in which white light outside is made of an infinite number of images of the sun. When we look at the light projected through a pinhole (even if it’s not round) we see a round image — one image of the sun. If we look at the light that goes around an anti-pinhole (like a piece of paper, even triangular) you see a round shadow… the opposite of an image of the sun!

Here is the antislit activity from Paul Doherty’s website. As he puts it, “The anti-slit removes one wavelength at a time from white light. Thus we see the spectrum of subtractive colors”