We've just finished our study of waves and the transfer of energy. Students must be able to explain the differences between sound and electromagnetic waves. It's one of the hardest units, really, since it's so technical. They have to know longitudinal, transverse, medium, energy changes, relationships between wavelength, frequency, amplitude and energy of both mechanical and EM waves. They also must know how waves behave. Harder than it looks, folks.
But I know that going in. So I give LOTS of examples, show lots of pictures, put things in their hands, make it as memorable and meaningful as possible.
Case in point: One part of the lesson goes something like this:

"Imagine we get on the Magic School Bus (Oh, yeah, I still talk about Mz. Frizzle, Her-Bad-Self!). We travel to outer space and park. Then we Vote somebody off the bus (This usually causes some discussion). We then kick him out of the door and slam it shut. "

At this point i'm getting my whole body into it. I want to create a memory for them that is very elobrate. They are laughing by this point.

I say, " We stand there watching him panic. What would we see and hear?"

I then mock bang and jump around with my eyes screwed shut and my mouth open in an agonizing scream. But I don't make a sound.

I say, "We wouldn't here anything. Because there is no sound in a vacuum."

Yeah, I know, space is an APPARENT vacuum, but in the heat of the moment, few of them will correct me.

This gets them. They tend to remember this. Which is why I make a fool of myself in front of them. To make it memorable. And it has been. Until this year when I got trumped by the girl who asked...

"Does that mean we couldn't even hear ourselves think in space?"

To which I thought REALLY HARD
"You would have to be able to think first, me girl".

Does that make me a bad teacher?