So I was teachin this lesson on Friday on the reflection of waves at boundaries right...
It starts off with a walk to burn down the school
"Who's with me!"
Everyone.
"Right, take your school jumpers off, wrap them around a long stick, dip them in petrol and set them alight. We're off to burn down the school!"
So I have on the board 4 parallel lines.
At the first parallel line I says
"Right the school is protected by a swamp. The swamp contains piranha that will nibble your toes. Then, when they taste blood they will devour you to the bone. To add to this you will have to swim with your torch above your head to keep it alight."
"So who's turning round?"
1 person.
fair enough.
So at the next boundary we get more hardcore and I say
"Right, in the Amazon river there is this type of fish, called the Candiru fish. Gents you may want to cross your legs"
"Basically, when you take a pee, the Candiru swims up your stream and embeds itself in your *whistles*"
"It pushes spikes out to either side and stays there eating your *whistles*
"So who's turning round?"
Most male hands go up.
Two more boundaries and I'm running out of ideas. So the crocs come in.
By now there are like 10 people left and I'm thinkin
hmmmm how am I gonna get rid of these ones...
So I say
"Right at this boundary there's a bunch of heavily mutated octopii. They have 25 legs each."
"And what they'll do is that if they get hold of you they won't kill you. Well not straight away. What they'll do is they'll stick their tentacles in your mouth, in your ears and up your nose. Then they'll look for any other holes they can find and slot their remaining tentacles up there"
"so...."
"Who's with me!?"
Anyway, the moral of that story is that at boundaries, waves will reflect if their situation changes too much, which is to say that if the density of the medium changes substantially they will mostly reflect.
For example, waves travelling from solids to gases will mostly reflect, which is why they put that jelly stuff on to your belly when they do ultrasound scans.
Man. I love my job.
