## Monday, January 14, 2013

### Pick a Fight!

Well, not really, but maybe a "physics fight"...

We had a friendly competition with a neighboring school today and Friday via Skype:
• Each school checked out a clip of "Despicable Me" this week (about four minutes, dealing with the rocket trip to the moon, the shrinking of the moon, and the trip back) and was challenged to model, debunk, predict, verify, etc. whatever they could. My class spent 90 minutes on this, and I think that the other school did about the same.
• I didn't give them any help or direction, except for telling the name of some new concept that they wanted, so that they could effectively index/Google on their own (terminal velocity, energy-mass equivalence, and shear strength came up)
• Each problem was whiteboarded, and we took pictures of the boards (some of theirs had nice electronic presentations, though).
• Today we Skyped and took turns: 10 minutes of presentation followed by 7 minutes of questions.
It's not really a competition, but it's fun to frame it that way, since they're used to having long-standing rivalries in sports against local schools.

The investigations were fun, and it was great for the students to interact with each other from afar. We're also planning to trade some screencasts with intentional mistakes in them.

If you want to interject a little more fun into the WCYDWT?/whiteboarding/Mythbusting/modeling paradigm, maybe you should pick a 'fight' with a nearby school!

Here are our whiteboards, from both sections that participated:

An analysis of the speed of the spaceship (not surprisingly, too fast for reality), using the altitudes of different parts of the atmosphere for reference:

An analysis of the mass of the shrunken moon, assuming that its density stayed the same:

...using that mass, the freefall acceleration and very-low-orbit speed for the tiny moon:

Assuming that all of that missing mass was converted into energy, the ridiculously large amount that there would be:

An analysis of how the now-tiny moon would basically eliminate tides:

This class assumed that the moon's mass would stay the same, rather than its density. A proof that this would do nothing to the tides:

Assuming CAPM speeding up and slowing down, the acceleration of the spaceship and the resulting huge forces on Gru, if he is going to make it to the dance recital:

The freefall acceleration on the surface of the tiny moon:

Trying to determine Gru's speed when he hits the shrunken moon (it shrinks to be at its center of mass, so he's one moon-radius away, and then he freefalls towards it); CAPM is used, with the acknowledgment that it's not appropriate.

Assuming that he hits the moon and stops in a short distance (stomach compression), the huge normal force that would be exerted on him by the moon when he hits it:

A comparison of the pressure exerted by that huge force and the shear strength of bone, showing just how easily that moon would cut a hole straight through him (and then he'd continue past it, slowing down as he moves, then back again, in an oscillation with the moon passing through the same hole over and over... OK, physics isn't pretty).