Day 121: Geometric Proof of Snell's Law

I think I'm liking geometric proofs in physics! There's something powerful about these derivations. I think that model-building isn't always just trying it out in lab; sometimes it's about using our model and mathematics to come to new conclusions which we, of course, must check against reality.

I got the animation above from PHYSCLIPS, which I had never heard of before today. It was great for visualizing the wavefronts and rays, but then, when I right-clicked and hit rewind, it paused the animation so I could do some geometric magic. 

Next year, I have to figure out how to make the kids do more of the derivations. But I've done proofs like this a few times this year, and I like it.

We practiced our new understanding of reflection and refraction for the rest of the day.