Hello and welcome to this doctor who special edition of Live Experiments where I'm going
to be having a look at where I think the science of this thing is, the Doctor's sonic screw
driver.
Now I'm here at the Faraday lecture theatre in the Royal Institution in London and I'm
joined by my companion for this adventure Andy from the Ri Channel
Hello everyone.
Now as the number one Whovian of the head Squeeze gang I was trying to think what could
we do for Doctor Who's 50th anniversary here on Head Squeeze.
And I got thinking about the sonic screwdriver and what I think, using logic, is happening
and how it works.
Sonic screwdriver, sound, to control things and that's why I gave Andy a call because
we've done a pretty cool experiment in the past demonstrating sound waves so why don't
you tell everyone what is going on here.
Sure, so what wave's got here, this is a classic piece of science demonstration kit.
It's called a Rubens Tube.
It's a metal tube with holes; tiny holes drilled all the way through, on the top so we can
pump gas through it from the regulator here and set fire to the gas that comes out through
these holes.
Very nice.
So that's quite pretty already I think.
But there is more to it than this.
As well as pumping fire through it we can play sound through it.
Sound of course is a traveling pressure wave, so if we're putting through sound the height
of the wave will tell us about the pressure at that point in the tube.
Yep.
So by putting sound in we're gonna change that pressure and see what happens.
I thought we'd start with the simplest sort of sound we get a pure tone or a sine wave
as we know in physics.
So with a nice little generator on my smartphone here.
Ok straight away we have a Standing Wave!
A standing wave, is when sound is coming out of the speaker, hitting the cap at the far
end, bouncing back and interfering with itself, so it's creating this system of nodes and
anti-nodes.
The standing wave because you're not seeing anything traveling and they're staying where
they are.
Yes exactly.
So here we have an anti-node and there as well, where the flame is small and that's
because the pressure is oscillating a lot, then we got a node here where the peaks are.
And that's where the pressure is staying pretty much steady.
Yeah, and that is modulating the rate in which the way the gas is coming out of the holes
and we're getting the different flame sizes.
Now we can change the frequency of the sound the frequency being pretty much the same as
pitch and see how that affects it.
Ok let's give it a go.
Oh wow!
So you can see that like likes some frequencies and it doesn't like others.
And that's called resonance.
Essentially what you want is to have wave lengths that will fit inside the tube and
that's the waves that will try and suck all of the energy.
Whereas outside of resonance you're not really driving it at the right frequency, so it doesn't
like to take on all the energy.
Wow.
That's all very well and good but it's not really Doctor Who though.
No, not really.
Well, it is a little Doctor Who.
He has used a sonic screw driver in the past to control flames, the girl in the fire place,
he put a candle on in that, and I think in the evolution of the Daleks he hit a Bunsen
burner but I think we can do something more doctor who-y.
I think we can we can play the Doctor Who theme
What could be more Doctor Who-y Exactly!
So we can see it flickering in fire.
So we're seeing a slightly different behaviour now aren't we?
It's not a steady sound so we're changing the notes all the time and there are lots
of different frequencies going on.
So the fire just dances to the music at those resonant frequencies.
That was pretty cool.
I want to do something that I've never done before with this Ruben's tube with you Andy.
I want to talk into the Ruben's tube.
Talk into the Ruben's tube?
Yep.
You might inhale a bit of gas.
No!
I've got a voice changing app; I thought we could do something a bit Dalek-esk.
This I can't wait to hear.
Exterminate, exterminate!
Andy thank you very much for hosting us at the Ri.
I won't exterminate you.
I'm very grateful to the Daleks for that.
Well thanks a lot Andy for having us at the Ri.
I'm no Timelord but I think we demonstrated some sonic screw driver principles with this
thing.
If that' not enough Whovian science for you head on over to the doctor who channel where
we recreate the original title sequence and if you're new to head squeeze why not click
on that subscribe button.
Should we do the time tune again?
Once more.
Lets do it.