I embraced concept, then definition today in a slightly new way today. We had already learned beats, but we had no way to explain it. After a bit on the Doppler Effect, we went into the hallway and watched a crest and a crest overlap as well as a crest and a trough. We practiced that with a few basic problems, and then looked at two waves with almost the same frequency. They seem to have constructive interference at one time and then it seems to go to destructive interference a little later. That explains the LOUD to soft to LOUD to soft to LOUD to soft we heard when we played two waves of slightly different frequencies. We can explain it now!
I really liked that a phenomenon they saw, they understood, that they even had a name for, did not yet have an explanation. But we can get to explanation with just a little bit of model building. And I don't have to walk them the whole way. I can just show the problem, and ask them what would happen, and let them tell me what that seems like they've seen in the real world.
(I showed the problem using this Desmos simulation that I made. I've included a picture below.)
That look of understanding, that look of realization, makes teaching so worth it. When I can make a terrain that they can then use, with their own creativity, to come to understanding, well, that's the best.