Okay this demonstration is a demonstration of standing waves. Now what I have here
is an oscillator, so it's just vibrating up and down. The string runs over it. So the
string is vibrating up and down but what happens is this sends that vibration down
to the far end. It reflects back. So now i have two vibrations. Typically they're not in sync
but if I get them in sync - the one going this way and the one coming back, let's see what happens.
So i have to get the right frequency.
And this is called a standing wave. It's because one wave going this way,
another wave is coming back and they are in sync with each other.
Now what happens if I keep going higher with the frequency.
Now i have a standing wave and you can see there's three loops.
this is one of my favourite demonstrations. It's called ruben's tube. Just like we did standing waves on a string, here we get
standing sound waves. On this end, I have a speaker. I'm going to send the sound wave down this tube.
It's going to reflect off of that end, so again I'm going to have two waves.
Typically they're going to be out of sync but if they get their frequency just right
so that they're in sync, we get a standing wave. Now what's cool with this one is
I've drilled holes along this pipe. It's filled with propane as we can see the flames along here.
When I get the standing wave where the peak is, it's going to push more propane out, the flames
will be higher, so we will actually be able to see the standing sound wave ,so let me show you that.
So there's a set standing sound wave and now I'm going to increase the frequency and see what else we can get.
So this is a demonstration of air pressure. What I've done is I put some water into this
big steel drum. The water is boiling so it's changed the water to steam.
So the drum now is filled with steam so what I do next is I'm going to seal it.
And now the steam is going to condense inside the drum.
As the steam condenses back to water, what's going to be left inside the drum? There's no air, there's
no steam, there'll be a vacuum. And now the air pressure inside is gonna squeeze this drum.
And let's see if it can squeeze it enough to make this drum collapse.