STEAM: Things that Spin

For the final STEAM activity of the year, I wanted to steer things towards active experimentation instead of just build and play (Transit of Mercury notwithstanding). I did not want to lose the sense of wonder I've been nurturing, however, so quantitative experimentation was discarded for qualitative. Experimenting with something with a surprising property seemed like a good idea as well, so I decided to base an activity on things that spin.

Spinning things, if you've not observed them before, can be very non-intuitive. The simple act of imparting angular momentum gives rise to stability, in most cases, and very unexpected behavior in others. To demonstrate the different behaviors, I assembled a small collection of spinning devices.

They're not toys. They're educational tools.

I started with an Euler's Disk acting as a very large and heavy coin. The "coin" at rest on its edge is inherently unstable and wants to fall over. But when it's spinning, it does not just fall over. The act of spinning the "coin" makes it want to stay upright.

Next, I used the top to reinforce this idea. The top wants to lay on its side when it's at rest. But if it's spinning, it will remain upright.

I then asked if anyone knew how to tell the difference between a raw egg and a hard cooked one (neither shown in the picture), then demonstrated the answer. I also showed that once you've got the raw one going, it doesn't want to stop, even if you halt its rotation momentarily.

I used the plastic egg to demonstrate when you spin an egg-shaped object fast enough it wants to stand on end.

The celt (rattleback) was then pulled out because it is vaguely egg shaped, but it does not act at all like an egg when spun. Especially in the wrong direction.

The dynamic celt was used to explore the action of the celt.

And tippe top was there to keep them guessing.

I then asked the class what they have learned about spinning based on observations of all the items, guiding them to the idea that spinning exerts a force, and the force is proportional to the rate of spin.

To reinforce this idea, I used the gyroscope to demonstrate unusual behavior when things spin really fast. I spun the gyroscope with a Dremel tool (a high speed rotary tool, for those who aren't from countries where the brand name has supplanted the noun) with a felt polishing wheel attached, so I got really good action on it.

After the demonstrations, I told the class I wanted to explore what it is about spinning that creates force. I had the students return to their desks where they found five squares of card stock with a small hole in the middle of each, and a toothpick. "We're going to do some experiments by making a top," I said.

Top, deconstructed.

 The first step was to try spinning the toothpick by itself and observe what happened.

The next step was to add one square about 1/3rd of the way up the toothpick spin that, and observe what happened. I solicited hypotheses from the students as to what they thought would happen when the second square was added.

This process was repeated for all five squares. At the end, I asked the students what they thought was required to generate the stabilizing force in a spinning object.

After that, it was top spinning time. And Euler disk. And plastic egg. Pretty much everything I had brought with me. Fun was had by all, and I got some really good hypotheses from the students about spinning things.

As a total aside, after I had designed this activity, Physics Girl published a video on bizarre spinning toys on YouTube.