Friday, November 11, 2011

"Honda Cog" in the classroom

I've found that one  good place to drop the classic "Honda Cog" ad into the physics curriculum is amid our lessons on energy transfers/transformations.

Those lessons begin with step-by-step analyses of a pole-vault and the firing of a toy dart gun (I'm a big fan of old-style dart guns).

Then we look at the Honda Cog ad.

First we watch it without interruption. Then we watch it with analysis. The video is paused, we discuss, then move on to the next pause-worthy event. There are openings to discuss energy transformations, equilibrium, Newton's third law, balanced torques, and more.

The one segment that students reject is the wheels rolling uphill (0:25-0:30 in the clip). They know that's fake.

So it's a good idea to have a Sargent-Welch Variable Inertia Kit (WL0707D) handy.

The intended use for these discs is to adjust the inner mass balls so that one disc has high rotational inertia and the other has low rotational inertia. The you race them down an incline. If students are unaware of the interior configuration, you've run a nice discrepant event.

But our purpose here is different. We need just one disc. Load the mass balls as shown so that the disc will behave like a Weeble.

Put the disc back together and set it in unstable equilibrium on an inclined plane. A slight disturbance will set it in motion—up the hill!

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