Counter-factual Animations and Energy

Soon after my students began energy, I presented them with a set of five YouTube videos that I made with VPython of a race between two identical balls, launched by identical springs that had been compressed identical amounts.

The five simulations present five different ways that the race could play out; one is physically accurate and, while the other four have some sort of logic, their results are not physically correct. The students have some time in groups to determine which they think is correct and, more importantly, what specific issues they have with the others. I'm challenging them to figure out the laws of physics in these four alternate universes, in essence.

After they've worked for a while, they vote, and then we go through the unpopular ones first, with students giving their reasons against them, debating as disagreement crops up.

It usually boils down to two or three, and they hone in on the correct answer pretty reliably in a peer-instruction-esque way. The discussion has been lively and productive, and I like it as a way to focus their attention on the kinds of things that energy conservation does and does not allow in the world in general. It also is a good review of some kinematics concepts, including average velocity and the velocity/displacement relationship.

The YouTube format isn't the best - the size is a bit too small, unless you want to switch back and forth between fullscreen and smaller. Additionally, the suggested videos pop-up at the end is distracting and annoying.

To that end, I coded the simulations into GlowScript instead; students can now deal with them in-browser, repeating or switching at will. It would be neat to have two windows to select different simulations to run against each other simultaneously, and I may add that feature in the future. In the meantime, this will be a big improvement for students over the previous incarnation!