- Hi everyone, I'm here at the University of Sydney today.
I've got one familiar face, Petr, over here.
- How is it going?
- And this one is Gabe and Liam.
- Hey.
- So, everyone here is interested in I guess physics, physics education and we've got some
experiments set up for you.
So, the first one we have here, you might hear cranking in the background, is the Van
de Graaff generator.
So, this is I guess all about static charge and electricity.
You can see a bit of a discharge of electricity between these two poles.
Maybe Petr or someone else has set this up.
Tell me what your explanation of it is.
- Well, so the basic idea is that, remember that experiment that you did hopefully in
primary school, maybe high school where you take a plastic rod or a ruler and you rub
it with a piece of cloth, a piece of felt and then you put it next to some water or
next to uh, like a tissue or some paper or whatever and that stream of water is slightly
attracted towards that ruler...
That is basically - it's separating the charges, right?
To create a pull, right?
So that's kind of what's happening here.
There's one part of this contraption is becoming really strongly charged and the other one
isn't as strongly charged and then it sparks across the air.
- Yes, so like an electric potential.
- Yeah, there's a gap.
As a rule of thumb, every centimeter that a spark arcs across air is between 15,000
to 30,000 volts depending on kind of the humidity and all those kind of things.
So that is –
- Around 10 or 15 centimeters gap.
- I would say 10.
- Yeah, I would say 10.
- So, yeah, that's a lot of volts.
Someone do the math quick, I'm not good at this.
- About 3000 give or take.
Three hundred thousand, sorry.
- Three hundred thousand volts.
- On a good day, this can do about 30 centimeters spark.
Today is not a good day, but we have had to do 30 centimeter before, which is –
- It's frightening.
900 - 900 Kilo volts
- So, Liam, so, you're saying there's 300,000 volts and there's a thing here and there's
a lot of us around and there's this foam thing on the floor.
- It's almost if it's a hot set up here.
- Yeah, I'm worried.
- So, the form is that it insulate you for the probably next thing we're going to end
up doing.
So that you can safely stand touching this and build up a lot of charge and we should
see hopefully some interesting things happening with that.
- So, this is so that I can safely stand and touch this.
What if I just touch it right now, what would happen to me.
- It would hurt, yeah, yeah.
Instead of discharging into the grounding ball there which is nicely connected to that
ground so it doesn't hurt.
- I would be ground?
- You would be ground, yeah.
- OK, so this is to stop me being the ground?
- Indeed.
- OK.
- Ideally.
- OK, so I guess we should try.
- Should we try?
- OK, so, it was an idea thrown around the fact, I know you [Inaudible] that when you
hold one of these, your hair starts to stand on the end because I guess each strand of
your hair has the same charge and like they start to repel each other with your individual
hair strands.
I have quite long hair I guess, so I could try take mine out and see if it does anything
on the generator.
My suspicion is that it - like my hair would be too heavy, like each individual strand.
I could, maybe the witness on the science [?] here, maybe you guys can try off today
but I've never tried on one of these since I've had [Crosstalk] on itself.
- Well, you could have tried to take science [?] we're better to go.
- Back to my classic science of long hair series.
- Yeah, possibly 15 at the moment, so that's probably around 400K.
- I actually have wooden rod [Inaudible] they change.
I did find it amazing but -
- You can feel it sort of attract when you see the spark bounce[Inaudible] the charges
are pushing back out.
It's a nice little bounce effect, I'm not moving it at all.
- No, I think it does have a good bounce.
- Yeah.
- That's so cool.
- OK.
- Alrighty.
- Anyone wanna demonstrate or I'm up first?
- You're up first.
- OK, I'm standing right here.
- Stand on it.
- Yep.
- Maybe take your watch off.
- It's normally totally safe but I don't wanna worry about breaking than hurting you.
- OK, you're discharging it?
- I'm discharging it at the moment, so what you need to do now, go ahead and connect to
the ground, so in order to build charge, hands on.
- Hand on now?
- Both hands
- Both hands.
It's better.
It's good at the moment?
I'm gonna now take the earth off.
- Yeah.
- So, you should feel anything anywhere?
- I don't feel anything.
- OK.
- But I can see the strands start.
- Yeah, I think you can start to see her hair moving.
- Can you give your hair a shake?
- Yeah.
- Give it a shake.
- Oh my god!
That's amazing!
- How does it look?
- That's so cool!
- Cameraman, how's it?
Are any of the longer strands like affected?
- They act like these longer strands should push out a little bit.
- And I didn't get my hair on the [Crosstalk].
- These shouldn't hurt you.
- Nice..
- "Shouldn't"?
- I might have to convince somebody to move if you don't mind.
- Alright, so John can you see that?
- Yeah, yep, I can see it a little bit.
- Is that a charged rod?
- No, this is just perspex, so it could be completely safe.
- So, it shouldn't be –
- You have no otherwise, it would have –
- I mean, this one!
You can see this one here.
- Oh my god!
That's so cool.
- Let's have a look at the back.
- That hair strand right there, that one is flying off, off the back.
- No, it's so amazing!
Holy crap!
- So, you know, this isn't the biggest Van de Graaff generator, I did the same, but they're
like much bigger ones that exist where the charge build-up would be a lot more.
- Yeah, absolutely.
- So, I mean, I don't think I can get all my hair standing with this one.
But maybe with a bigger one.
- But seriously so impressive.
- I mean, that is still quite - had to get a picture of you.
- Yeah, that's amazing!
- And you can see, it's clearly affecting the top hair.
All the hair at the top is absolutely -
- The first impression that I have now which is slightly scary is how conductive is hair?
If I touch one of your strands of hair -
- It's kind of [?] isn't it?
- will this discharge?
Will there be a spark between -
- I don't think so.
But if you do touch the ones at the back.
- Yeah, this ones here.
- OK.
Oh!
It's slightly - it's pulling towards me.
Oh, that's pulling away.
That's pulling towards, that's pulling away.
- So, you are exchanging charge there, yeah.
- Yeah, yeah, yeah.
- Wooooh!
- You are stripping electrons out there.
- Can I release myself from this without getting [Crosstalk]?
- Toby, do you feel that?
- I can feel that.
We have a spark.
- That's amazing.
- So, just hands straight up.
- Hands straight up?
- And then just step off.
Don't touch anyone or anything and you should ground, your hair to drop straight down as
all the charge goes straight in the earth.
- OK, I'm gonna lift my hands off.
- And straight off, and then step back.
Step back on the ground without touching, and your hair dropped.
And maybe bang the table a little bit with your hands before we move on.
- Yeah, touch the table.
- before you touch metal.
- Oh my god!
That was awesome!
- Very good.
- Nice one, hey [?].
- Getting a spark.
- Yeah, OK, well, my hair is pretty long, how about someone with short hair try.
Petr, you should go.
- This should be getting discharged or something.
- Yes.
- Cool.
Every time there's still a tiny spark.
- Let's go.
- Alright.
- I mean, there's always gonna be some -
- So, I think, Toby, this might be your experience as well, every time I do this, there's this
um, like I know the physics and I know that it's safe and I trust the equipment and I
trust Liam and I trust the amount of years of education I have, but it still feels weird,
and this still feels scary and slightly wrong.
- Yeah.
I remember this was like one of this was like one of those physics class.
But here I'm like, yeah, now I was like telling you guys like I was scared.
- Yeah, it is.
- And it's like this-
- Well, we got the [Inaudible] only had this one, over here.
You can see the bottom is styrofoam and no one would stand on empty [Inaudible] until
I show you it was safe.
But I wasn't quite sure because it got metal on top, how safe I would be when we charge
this.
Sorry, I had to get up there [Inaudible].
- OK, so, Petr's hair, I don't know [Crosstalk] but I can see [Inaudible].
- Yours was good.
- Yeah, yours was really impressive.
- But yours is doing really well, yeah.
- I can't see it.
- I know, I know, here, I'll show you.
- Yours is definitely standing up now.
Your hair was down here before.
- Can you see it?
- Oh wow!
- It's pretty good.
- Yeah.
Oh wait wait, as soon as I let go -
- No, as soon as you got one hand on, that's fine.
- No, but I feel - I feel
- So, you can actually take your hand off and put it back.
- Whoa, wait, whoa!
Whoa!
Why is it making that noise?
- What?
The crackle?
- The discharge.
- Whoa, you'll have a different potential between there and there.
- Yeah, 'cause you got [Crosstalk] going on in there as opposed to your head.
- So, you can actually, don't do it yet, but you can take your hands off a little bit and
then put it back on for like a few seconds.
Look at that, I just saw your hair drop.
- You're doing that.
- Yeah.
- Because the charge is going to you and not to me.
- Yeah.
Well, you see, now I'm acting like a lightning rod.
- I can hear them still charge.
- God, that feels so weird!
- Yeah.
- Alright, so, what I'm gonna do now is I'm gonna let go of my hands and then I'm gonna
put them back on in a couple of seconds.
- Yeah, in three seconds.
- And he should store the charge...
- Because your charge should be the same.
- Right.
- So, the reason you're not getting shocked is because you're in the same charge as it.
When you take your hands off, you should stay relatively the same charge 'cause you're insulated
from the ground and that's not gonna build up too much more charge.
So, you'll take it off, and put it back on and you shouldn't get shocked.
- That's the whole thing with the electric potential.
- Sure, I understand the theories.
- You just wanna hope it's like, you know -
- So, a year ago, there was the show with Todd Sampson called Life On The Line and like
I thought the premise originally was kinda lame and then like genuinely when he did a
bungee jump with - with a phone book like connecting the two elastic wires, I was like
"man, this dude gets it".
Like, this is actually insane.
It's like one thing to know, you know, the theory and the tests of it and then the other
thing is to actually bungee jump with a phone book.
- Gotta have a lot of faith in the math, right?
- Yeah, yeah.
All right, so, three, two, one.
One, two, three.
Aww!
- See, the hair does not drop back because you still on the -
- Yeah.
- Oh, Oh, I just sparked it across the table.
- It will jump into the table, yeah, because that's, earth.
- So, I get off, I'll discharge and then we fist bomb again.
- OK, we'll do it.
- Alright.
- There we go.
- You still got some charge.
- I can still see your hair standing up.
- Yeah.
Just hit the table, you'll stop a bit.
- Oh, so good!
Physics, I'm I right?
- Good science guys, good science.
- Good science.
- I mean, I'm not sure if that was the spark or that was the actual wire.
- That was perfectly timed with the spark.
- Did we not turn the lights off?
- Well no, no.
There was absolutely no time.
Some time it takes up like [Inaudible].
Like we know we've done too much when that clock at the back just turned into gibberish
and the - well, if they down then go back in the roof.
- You've done too much physics when the clock
- Yeah, the clock take on that is cool, it's been real right down here.
- We've decided to quit physics for today.
- Yes.
- OK, so we're rummaging in this cabinet looking for some more experiments to use and Petr
pointed out this strangely melted piece of metal and he told me that this is a lightning
rod.
- Yeah, it's a lightning rod that actually was at the University of Sydney and it was
hit by lightning and then all the current around it basically created a strong magnetic
- magnetic field that basically pulled itself together.
So, it deformed from like a solid, like the pipe that it is with a hollow opening as you
can see and like the pipe shot itself and it closed itself off there.
Pinched itself together.
So, it's actually called the pinch effect and there's a demonstration of this here and
we're not doing it because one of the transformers is broken and we don't want to blow anything
up.
But if you put current in here, it basically does that.
- Yeah, and that's what happened to this little thing.
- Yeah.
- Alright, let's go and do some more experiments.