Another example of resonance will be, ahh... shown by Mr. Coates with this tube.
Inside the tube, there's... there's gas.
So we have a gas column inside,...
...which we can, ahh,...
...prove to you by lighting the small gas jets,...
...which will come out through a series of holes drilled to the top.
Ahh... and there, everything is virtually static.
The gas jet is just sitting quietly inside.
Small amounts of gas are coming out,...
...and the height of the flame indicates the pressure of the gas.
Now this... this column of gas is capable of vibrating in a longitudinal way,...
...and we have arranged that we can set it going...
...with various resonant frequencies, by way of a loudspeaker...
...that can be tuned, and is placed at the end of the tube.
So, if we start off with a certain note,...
...then you can see that now we have a longitudinal vibration,...
With, ahh,... one,...
...two higher notes.
One, two, three... waves.
Ahh,... One, two, three, four.
And a succession of waves.
That's fine, thank you very much.
These waves are...
...are associated with the pressure variation,...
...as the gas is compressed and extended...
...ahh,... through the excitation provided by the loudspeaker at the end.
Yet another example is the, ahh...
...is the vibrating plate.
And here we have a steel...
...plate, rather a thin one,...
...and so, fairly flexible.
It's secured at the mid point, held down there,...
...but otherwise free to vibrate around the edges, and everywhere else.
And, at one edge, we have a little vibrator, which can be...
...controlled by an oscillator, which I'll now switch on.
And you can hear the frequency...
...being generated on the plate, but you can't actually see the plate moving.
Even though you can hear the noise.
Now, I'll try and get a large...
...frequency set up here.
I think we might be able to see that if I sprinkle some powder on the top.
This light powder is very light indeed,...
...and, as the plate bounces up and down, in various places,...
...so the powder bounces with it.
And, gradually, it's bounced off the parts that are moving,...
...onto the parts that are still.
Now, we can produce various patterns with this...
...arrangement, and here we're driving the plate.
Now, at a certain frequency,...
...in which the powder is bouncing around quite merrily, and forming a certain pattern,...
...accumulating in the one side of the plate in that case.
Let's try another frequency, higher up.
And that's quite a nice pattern coming up, I think.
Now, parts of the plate are going downwards, and other parts are going upwards.
And the parts in the middle are...
...stationary, or virtually stationary,...
...and that's where the powder is accumulating.
Perhaps one more frequency, at a higher...
And these, ahh... these patterns are... are displaying the...
...very complicated mode shapes that arise...
...if there's some external excitation taking place...
...which, ahh... coincides with an actual frequency in that particular mode.
So, there's some interesting patterns that we can reveal...
...by, ahh,... small experiments of that kind.