Inquiry Stylee: Acceleration (Wiimotes!)

My secret objective is for them to think of an idea and follow it to fruition in a scientifically meaningful way. That’s it.

I’ve introduced Energy Conservation already by this time in the course, and the next towering giant to be seen is Newton’s Second Law. I know some of you will find this approach to be crass, but my kids don’t seem to benefit from the traditional way that physics is presented.

Why wait to introduce these huge ideas until kids have done all sorts of kinematics and other mathematical abstractions? I know the standard arguments for book structure, and I disagree: We’re always “preparing” them for the most important idea. Screw that. Give them the important ideas and flesh them out as the year goes on. Things will start elementary (i.e. Just KE and gPE) and move into complicated abstraction as their understanding follows. Energy conservation and F=ma are pretty much the only things I want me kids to remember, so why not stress them throughout the whole course?

How to teach F=ma, the eternal quandary. So simple, vital, and nuanced. I know it hinges on their understanding of acceleration. Acceleration in turn is one the trickiest topics to teach, not because it’s hard to manage, but because everyone comes with misconceptions about it. English usage of words like acceleration, velocity, speed, and their ilk are totally muddled. I need kids to understand the differences between them. I need them to understand how units underpin the connection of math to the sciences. I need them to reject their current misunderstandings about the magic pushes and pulls that comic books and movies have shown them.

This type of teaching towards misconceptions is not new, but I think it bears reminding. If you ask a student why something continues to move after you’ve thrown it, they will often respond with something quite cobbled and illogical:

“Well the force from my hand is like still pushing it in the air, and when it runs out of force, it falls to the ground.”

Yikes. A little evidence for the maligned “ontogeny recapitulates phylogeny” theory (which is a bit bunk, just to be clear): This child is positing Aristotle’s position, and she doesn’t even know it! This theory worked for a few centuries, but in the end it just doesn’t match all the data we have today about how things move. Our current most-used theory connects force to acceleration. That is, if something doesn’t feel a force, it doesn’t change speed. Whether from stop to go, or from fast to slow, those changes require a force, and that’s that. If you’re not feeling it, you’re not changing it.

How can I address this misconception? Wii Remotes! What? Yes! Wiimotes happen to the be the cheapest and most fun accelerometers on the market. There’s a slew of websites dedicated to jail breaking and otherwise non-traditional uses of your Wiimote. I use a piece of software called DarwiinRemote.1 Kudos to the development team for this community-driven gem.

A quick bluetooth sync (hit “Find Wiimote” and then hold down the “1” and “2” buttons on your Wiimote), and you’re up and running! Notice the awesomeness that is the real-time graph. Notice the fact that the Z-axis is offset by negative g when the Wiimote is sitting still. *Geek Out*

What using the Wiimotes gains me is a little street cred. and some serious connections to things that they want to know about. How does this thing work?2 How does it know what I’m doing? These are questions anyone has asked when interacting with a video game, let alone one as revolutionary as the Nintendo Wii.3

How does this go in physics class? We drop them. We slide them. We put wheels on them and make Wiimote cars. We put wings on them and throw them out windows. Whatever it takes.

We do a lot of great experiments with the Wiimotes. I generally start an inquiry cycle with them. My guided investigation is usually along the lines of dropping the Wiimotes, or attaching it to a pulley with a constant force. Anything I can do to help separate the ideas of acceleration, velocity, and force. The kids then think of all sorts of insane things to do with these. As I’ve said earlier, my goal is to start them off with something simple. Almost painfully simple really, in order to get them thinking about what could be cooler. My secret objective is for them to think of an idea and follow it to fruition in a scientifically meaningful way. That’s it. If it takes a short lame investigation to model a piece of technology, then that’s what I’ll do to get them thinking.

I’d love to hear your ideas about what you do with this! These Wiimotes come back all semester. What they’ve gained for me is a foothold when talking about F=ma at the board. (I spend more time at the whiteboard than you think). We’re always fighting to connect board ideas to real experiences. My favorite battle.

1. This is OS X software. If you have a PC, here’s a link to a similar program, but I don’t run Windows, so no promises.

2.The Wiimote is actually a camera with a bluetooth transceiver in it. The sensor bar is a misnomer. It’s actually just two infrared diodes that shine into the Wiimote camera. The placement of the dots from the sensor bar in the picture taken by the Wiimote conveys where the Wiimote is, which it then sends back the Wii via bluetooth. The accelerometer and other data are also sent to the Wii via bluetooth. No information is actually sent to the sensor bar!

3. Shawn Cornally is not affiliated or being payed by Nintendo, but he wouldn’t mind it. I’d look great in blue overalls, or perhaps a green tunic…