Play-Doh meets Vector Cross Products

My wife is a nuclear engineer who followed her dream of becoming a high school physics teacher.  I’m an electrical engineer.

As an aside, our “pillow talk” can get rather geeky. 🙂

Tonight when I got home from work, she asked me to pretend to be a student while she practiced explaining angular momentum; the current topic for her AP physics class.

Angular momentum involves vector cross products, and that causes vectors to go in all sorts of directions.   Trying to show vectors in all three dimensions using the weird supposedly 3 dimensional looking drawings on a 2 dimensional chalkboard falls flat (geek pun) as an explanatory tool.

So, we got some pens and I held them while she moved them around, but we soon discovered that more than our four hands were needed to hold everything “just right” and it was tough to move the whole thing around so the students could see it from different viewpoints. We looked like we were playing the old game of Twister and that might make it difficult to keep the students on track.

Then it hit me.  I got some shish kabob skewers, broke them in half so I’d have more vectors and stuck them in an apple…the apple serving to hold things in place so the whole thing could be rotated around so the students could see that even though the skewers…err vectors…may be at weird angles, they are still perpendicular to one another.

My wife made the observation that the skewered apple would only last a short time, and decided that Play-Doh would hold the vectors as well as the apple and have the benefit of lasting longer.

So most of the evening, she’s been sticking shish kabob skewers into a little ball of Play-Doh and moving the thing around while she rehearses her presentation.  It’s actually fun to watch.

When she finished with the momentum stuff, we somehow we got onto the topic of what happens “if one drilled a hole all the way through the earth and jumped in”….Newton’s shell theory, among other things, leaps to mind.  It’s late and nearly time for my head to hit the pillow….uh-oh…. 🙂


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