Thank you for having us here tonight.
Like Tom said,
I'm from the Wonders of Physics my naprogram.chel.
And we are hosting this week, David Willey, who is a teacher
at the University of
has a traveling show of his own Pithat goes out to schools, he
similar to what we do.
his show for you all tonight. So He just informed me he wonon
the Presidential Teaching Award last year.
( applause )
entertaining stories about And he also has some very
world's hottest fire walk and hthe world's longest fire walk,
actually taking some data to try to figure out
what fire walking is all about. ( inaudible )
There you go. So without further adieu,
David Willey. Oh, he's also the Mad Scientist
from the Tonight Show with Jay Leno.
So you may see him on TV. ( applause )
So, there you go. >> Welcome.
I've got to inform you
One, I'm not using my own equipment, which will throw me
off a little. And two, I don't have
my wife here with me. She usually helps with the show.
And as every woman in the audience knows, without
your wife, you're usually totally lost.
So if I stand up here looking totally lost, that's why,
because she's not with me.
will tell me what's going on. I've The very first thing that
I've got to do is give you
Often, what we do at the start a little bit of a warning.
a great big pendulum rigged up. It's just a bowling ball
on the end of a piece of chain. And I pull it back to my face
and I let it go.
of energy, because of course, it doesn't come any higher
than I let it go from.
except for two times And that demo always works.
Now one, don't push the ball. ( laughter )work.
Okay? That's not a good idea at all.
I've never been so stupid as to push the ball.
The other is, don't lean forward
( laughter ) after you let it go.
to do that. Usually, you stand with your
head against a wall, swearing that it's there so you that you
can't possibly move your head backwards, when what it's really
there for is so that you know you haven't moved your head
forwards. So, we were at a Catholic school
in Pennsylvania, and
I leaned forwards to keep I let go my balance,ing ball.
only about two inches.
an inch and a half too far. ( laughter )about
The bowling ball comes back up, hits me in the nose.
I've got to admit, it didn't
boy did it make my nose bleed. really hurt all that much, but
stage, 200 little Catholic kids So thin front of me,ing on
blood streaming down the front. They're all,
"Yeah! Great demo!" And I'm like, "No!
I'm not supposed to be
So, but we don't have the bowling ball, so I can't show
you the one that hurt me. But I can show you one
that just embarrassed the heck out of me one time.
Just to give a warning. I'm at a physics meeting
in Pennsylvania, and
pretty young teacher I'm listening to an admittedly
And the classic demo is where you take a piece of paper.
and you set it on fire. And then, once it's going
nicely, you put it inside a cylinder, and it's sticky.
Whoa! Do that again.
Sticks it to your hand. Or at least, it should've
stuck it to my hand.
to stick to my hand. Let's see if we can get it
It sticks. There we go.
that it's stuck to my hand, Anyway, you'right. to imagine
And the guy says, "The reason this is sticking to my hand
is because all the oxygen was used up."
I said, "Yeah, but there
of carbon dioxide formed. What's actually happened is
that you've heated up the air,
Let's see if we can get this it expanded."
"It expanded, and then to work again.
it tried to contract again, whebut of course,wn,
it's in a fixed volume there. So what happened
was the pressure went down. And that's the partial vacuum
is what stuck it to your hand." Well, he didn't like me
telling him that he was wrong.
revealing a belly that makes it obvious that he likes beer
a lot, and sticks this to his stomach, and says, "I can
do it better than you." Well, I've got an ego
that basically just about fits in this room.
So I figured well, "I've got
because I've got apparatus a better demo than you do,
( laughter ) you don't have."
And I go around and go, "What do you think of this?"
It stuck there firmly.
to do it. "You're really weird, David."
"No, I'm not. What do you think?
I look like a unicorn, huh?"
for a while, I figured Well, after doing this
with what we were doing. we ought to get on
I popped this off the top of my head.
Everybody bursts out laughing.
I haven't said anything funny Ithat I know of..
My wife is on the side of the stage.
She reaches in her handbag, takes out a compact mirror
and says, "Look at the top of your head."
There is this huge hickey.
Two weeks I have this big, ( laughter )
I looked like an idiot red spot on the top of my head.
So, when you go home, iyou do not try these thingss.
on your little brothers and sisters.
Let's start actually warning
of physics usually start. over moNewton's laws--he laws
We actually have a Newton in the audience, right?
A beautiful name. I usually promise the kids
in the schools that I do my show
during the show, that if they behave themselves
off as a holiday. theyAnd hence they all agreeday
to this.
so you obviously know And Ithat Newton's birthdaying,
is December 25. ( laughter )
But it keeps them quiet for about an hour.
Anyway, Newton's first law--
Newton's first law He had what, three of them.
I hate this, but ow! says a body--
unless a force acts on it. A body at rest stays at rest
that piece of red modeling clay, So unless I push or pull on
but sit there. it isn't going to do anything
What color is it? AndOh, it's blue.e--
Okay, neither is the blue in the back.
You see, I can move around. Now if I do set it in motion,
it then what? Carries on in motion until what?
I exert another force on it and take it off my head.
I'll need this later. I'll keep this bit
and look at another thing.
doesn't want to move Newton's law says the body
And the second law says that unless we put a force on it.
the bigger the body is, ifthe more mass it's got,it,
the smaller the acceleration
So I've got a nice, ibig mass here.
A lot of inertia to it. It really doesn't want to move.
Now if I put a force on it, of course, I can start it
into motion.
very hard on that, because Anybody notice I didn't pull
friction I've got on the table. I was kind of hoping not much.
Because what I want to do now is see, can I give it
a big acceleration
Well, there's a built-in by putting a big force on it.
And that is, I can't put safety guard here.
the paper towel will tear if a big force goes on it.
What I'm hoping, of course, is yep, I can pull that out
from underneath the bottle. And the bottle
stays virtually in place. It moved a little.
While I'm doing this
one of the kids afterwards at a school a while ago,
"Oh, that's the same came up to me and said,
the magician pulls a table cloth as the magic trick where
Crockery, or dishes, away from underneath..."
And I try to explain to kids as you call them.
that I'm not a magician, that when I'm in the schools,
There's a big difference between I'm a scientist.
A magician will do something a magician and a scientist.
how it works. A scientist will do something
and they won't shut up about it for the next three weeks
with regards to how it works. So anyway, I figured I've got
to incorporate this in the show.
some dishes, and a table cloth. So we Ooh, plastic,ckery,
must be for a picnic. And with any luck, if I do
my bit right, yep,
does her bit right. And I can get the table cloth
out from underneath the crockery.
Now I want to show you
physics demonstration. my all-time favorite
demonstration I know. Are you watching carefully?
( ball clunks on table )
No, honest. That is the greatest demo
I know. The reason?
It's never gone wrong.
Every time I let go, ( laughter )
Yeah, everything else in my life that I've done,
I have messed up at least once. If my second wife was with me
tonight, she would tell you that that's the truth.
( laughter )
everything really badly once. But this, if you let go,
it will fall down.
ego, I want to hear this In fact, I've got a big enough
I'll do the "If you let go", come from you.
Okay? you do thIf you let go.l down."
It will fall down.
( laughter ) >> That was pathetic.
It will fall down! If you let go!
a quiz on this later, because of that first response.e
Now down is what? Down is towards the center
of the earth. I've never actually tried it
with this particular hoop before.
And usually, this is the most difficult thing I do
all evening.
I've got to manage to balance Itthis piece of chalk.t
That's not going to work. How about we try this pen cap.
Everything's a piece
if you look at it right. of physics apparatus
We'll balance that on top. There we go.
to try and do now is see if I can get this hoop
out of the way. And in which case, if I can,
what? The pen top ought to end up
in the bottle.
Yep! So let's see if we can do it.
( applause ) Every time.
We said Newton's second law Gotsays what?at!
Force equals mass times acceleration.
I try and convince people that this has relevance
to their every day life,
We're going to do a demo now especially when they're driving.
some models. where we're going to use
I'm going to get it to the right shape.
This is a model of your head. Yeah, I know,
it looks more like my head. It's a model of your head.
Your head, going along
50 miles an hour. I can't run that fast, but what?
You could certainly be
I really hope this never, ever happens, but God forbid,
that vehicle is in
with an 18-wheeler truck. a head-oBam!llision
The truck hits the vehicle
really quickly. Because that's what Newton's
second law says, right? If you want something
to stop really quickly, you've
And the vehicle stops. got to hit it really hard.
Right, if you don't have You don't necessarily stop.
have an airbag in your car, ayou keep going until what?
Until you hit the windshield. Now, this is not--
It doesn't look like
it'll act like a windshield. a windshield, but
That stopped the head. Watch how fast--
that happening to my head. I would not want
a pretty big force, You can because what?have been
It put a pretty big dent
Now, if that's the windshield in thiand this is a head, clay.
we also need is we need a model of an airbag.
I'm going to get
to give me a hand if you would. I'm going to hold this up.
This is our airbag. Let me just show you
how to hold it. I'm afraid I'm going to have to
block your view a little. It's a fitted sheet.
If you hold it by the corners,
a "J" shape. it'll hang in a kind of
against it, it won't roll away, it'll just drop in the bottom.
Now, this has got some give to it.
This makes the collision
So this is the equivalent of the airbag.
And in a collision, these are your alternatives.
Hit the windshield. Head stops fast.
Big force.
Has some give. Hit the airbag.
It doesn't have to be Collas big a force.ger.
Watch.
( laughter ) You don't seem impressed.
I did not want you This is very good.
Because right now, to be impressed.
In science, I said what? I'm not doing good science.
it doesn't have to look like the If you're going to use a model,
work like the real thing. realThis, throw me your head to
a minute, mate. ( laughter )
This doesn't work, right? I think we'd have road pizza.
I don't think we'd have just a dented head there.
So if we're going to do good science, we need
a better model of a head. It just so happens that
I've got a much better model
Now if you decide to do this of a head here.
Make sure that the head does not have a cracked skull.
The shell of the egg
What's the squishy stuff is the skull.
That's the brains, yeah. on the inside?
a cracked egg by doing this. And make sure it's not
and the bottom. Okay, it's not cracked.
I really am squeezing that as hard as I can.
Oh, show your friends.
by squeezing it, Look, you can't crack an egg
The reason, of course, and you hold it like that.
It's a symmetrical arch. you can't crack it is what?
this shape. TThat's why that looks like
a tiny model of a sports dome.
Sure, you can't break it It's symmetrical.
Then hand it by squeezing it that way.
( laughter ) to your friend this way.
We don't build bridges They'll take it off you.
Yeah, you know what happens. that shape, do we?
You're just pulling out of your driveway, five miles an hour.
We still good?
Now in case anybody thinks Yep, we're good.
at five miles an hour-- yoI think in this crowd,t
nobody's going to be that silly.
and I get the sort of, But I'm in school sometimes
You don't need seatbelts "Oh, you don't need an airbag.
five miles an hour..." if you're only driving
oh, 14 or 15 year-old totally immortal little boys.
And I tell them, look,
a seatbelt and airbags if you don't think you need
Two or three of them stand up. at five miles an hour, stand up.
Put your chin proudly out. Put your hands behind your back.
into a brick wall. Walk face first
break your nose, right? NoAnd that's onlyto
three miles an hour.
almost double the speed. Five miles an hour,
Oh, you're definitely going to do damage to your nose.
Twenty miles an hour? Still good?
Yep, we're still good.
Speed limit in Wisconsin is? Definitely need a seatbelt.
( laughter ) 75?!
what do you personally drive at. No, I didn't ask
65? Okay, I can throw this egg
at 65 miles an hour.
I can't throw much faster. I've got to be honest.
making real money If I instead of teaching.eball
No, I couldn't take the steroids.
But at 60 miles an hour.
Did we break the head? Let's see, gents.
Give these two gentlemen No, we didn't.
Thank you very much. a big hand for helping me.
And just in case anybody's ( applause )
that was a hard-boiled egg, or that wasn't a real egg.
Oh, yes, that was a real egg. We make sure that
we put our seatbelts on.
It's a really good idea. We have airbags in our car.
another motion for a minute. I want to talk about
translational motion, Rigcars moving from one placeut
to another. Another type of motion is what?
Rotational motion.
Newton's laws. But it still follows
A body in motion A body at rest stays at rest.
But this body wants to stay in motion in a particular way.
An in fact, if I can get
to come and help me. that young man there
You look pretty strong. Here's what I want you to do.
Hold this in front of you.
And twist it, oh, he knows, back and forth like that
as fast as you can. That's pretty good.
He's doing it pretty fast.
Let me get it to rotate Now, lin a vertical plane,otion.
an up/down plane. It wants to stay that way.
It doesn't want to change.
as fast as you can. Now, when heGo on. to move it,
( laughter )
I love the sound effects! Thank you.
Yes, whoa, it's tough, isn't it?
give it back. I'll Thank you.hat,
These people are going to give you a big round of applause
for that. ( applause )
Thank you very much.
the same way. It What I've got hereng
is a turntable with some
If I make this go this way pretty good bearings in it.
standing on the floor, around while I'm still
It took quite a bit of effort. I can turn it over.
in the opposite direction. Now it's rotating
we've got an isolated system-- Newton's law says if
And something's rotating I'm going to stand on here--
something is going to have to keep rotating in that direction.
If it isn't the bicycle wheel,
Quite controllable. itI can stop.me.
I can start again.
the bike wheel, because why? I don't go as fast as
than the bike wheel. I'm a lot heavier
Now, I'm not sure if we can do But it wants to keep going.
If you let go? the next one, but we'll see.
Okay. If you let go of just one side.
Let's make sure we see which side is which.
If I let go with my one gloved hand--
I used to make Michael Jackson
I don't do that in schools any more.
( laughter )
If I let go with just my gloved hand,
will that side fall down? How many people say yes,
it will fall down?
it won't. HowAh, you're wrong.no,
( laughter )
Actually, what they're thinking of, I hope, is this.
If you get it going fast
by just one side-- and you support it
Yes, check that out. Let me see if I can do it.
by just that one side. It stays supported
We've got ourselves a gyroscope going here.
A means of steering rockets when you're away from
a magnetic field that'll work.
Another quick look here. Okay.
I want to have a race. Oh, I know.
to come and help me. I need a young lady
Cool. These good people
who let you out.
Shannon, I'm David. Pleased to meet you.
You come with me. We're going to have a race.
We're going to see who can empty
This is just colored water. tNewton saw me put water.
and food color in here, so that's all that is,
is colored water. It's just to make them
different.
You take the blue-ish Whilooking one.nt?
I'll take the red one.
start drinking. On the c>> No!f three,
( laughter )
No? Okay, I guess what we'll do
is we'll just empty them
But I'm going to win. There's a good
scientific principle
I'm going to cheat. beAll you're allowed to don.
is turn the bottle upside down
as you can upside down. Can you do that for me?
Sure. >> You promise?
Okay. >> See, this is why you ask
little girls to do it and not boys, because
girls keep their promises.
Okay, you turn it upside down and hold it as steady
as you can. All the way.
You start first.
I put a swirl on my bottle I start second.
Now, regardless of the fact that you started first
I win every time, which wasn't really fair,
was it, Shannon?
will give you a nice, big hand. But ( applause )these folks
Why could I know
Why? I was going to win every time?
what was going to happen. Air, light stuff, was going to
try to get up into the bottle.
was going to try to get out And waof the bottle.tuff,
I knew they were going to get in the way in the neck
of your bottle, and it was going to make
the water in there gurgle.
going to come out very fast. And it just wasn't
I put a spin on it. And the water tried to move
in a straight line. It couldn't, because
of the walls of the bottle. It effectively got thrown
to the sides of the bottle. Now, if you think about
what was happening
As I say, air trying to get up, water trying to get down,
they gurgled. That's the same thing
that happens with a flame.
a flame gurgles, of course. So now,Uh-oh.n't say
I told you I was lost without my wife.
We say a flame flickers.
is happening. Light stuff, hot air,
is trying to get up.
is trying to get down. Cold stuff, cold air, heavier,
in each other's way. They're getting
We don't say it gurgles. The flame flickers.
on there. ThaNow, if I take thisown
and I put it on top,
I'm hoping we can get the air and we puto spin. on this.
Now the light stuff ought to stand a better chance
of getting up the inside. Let's see if we can do that.
And indeed we can.
little tornado going. Before it gets too hot for me
to do it, just in case
in the audience, there are geography majors
Southern hemisphere. wait for it.
Hey, a knowledgeable audience! ( laughter )
"Uh...?" I usually get kids going,
Pull it off. Okay, now, stop that.
kill the flame. How can I do that?
Put that cap on top.
for something to burn, right? ThrHeat, fuel...ded
What's the other thing? Okay, I heard
some people say air.
You're both right, because Some people said oxygen.
about 80% nitrogen. There is some other stuff
in there, but they're the two basic components.
Things need air to burn.
a really cool demo A friend showed me
that he'd learned about things burning in air.
He'd spent a little time down at the space camp in Florida.
They showed him a demo as to
He couldn't wait a model of a rocket engine.
He said what you need is a five-gallon water bottle.
Which one is this?
I had to make sure Oops, wrong one.
You need a five-gallon we get the right one here.
You need some ethyl alcohol, water bottle.
You pour some of that in the water bottle.
And then, you've got to mix it up.
Because we said what? To burn the fuel,
it's got to be mixed with air.
carburetor doing this, In your car, it'll be the
Here, it's got to be me or thdoing this.ctor.
But now, we ought to have a model of a rocket.
I can't send it off, because
But I'm hoping that we can the ceiling is way too close.
pretty much as a rocket. still have it work
Let's see if it does. ( louSure enough, it does.
If we cap off the top,
As it gets cool, notice what happens.
I don't want to take it too far, it tries to shrink.
creases in the bottle, which is otwhat happened to this one,y
which is why I didn't use it
After he showed me that, again for that demo.
If you can do that with alcohol I from the chem lab..
Maybe I can do it with alcohol
Isopropyl or rubbing alcohol. fSo we tried it..
And guess what, you can.
isopropyl alcohol in here. So let's mix some
the one that acts almost like a carburetor.
I've got to mix the air with the fuel.
And this, because the alcohol has got much more water
in it this time,
Sometimes, it doesn't burn it won't burn as fast.
But I'm really hoping this time it burns.
Let's see if we've got it.
Whoa! My guess is there was some
ethyl left in there from the last show,
because that went a lot quicker than it usually does.
Now if you can demonstrate
maybe we could make a model of rocket engines with that,
Now it's not a scale model, a because this is my cylinderne.
and this is my piston.
I've got to admit. So it's a little undersized,
the ethyl alcohol again-- Actually, let's use this one.
A little of that in here. Put this cup in top.
Again, I've got to mix the fuel with the air.
So I'll mix the fuel
This time, I've got to make sure with the air.
in there. tBecause when this paper cupl
comes out-- Let's make it
a double paper cup--
to come out with it, again. IYeah, that was a bad showol
when it did.
paper cup to come out of there. Le( popping sound ) get the
And sure enough, we can.
to get covered in glitter. Don't look up, you're going
to put the flame out. ( light laughter ) going
I did this demonstration
about a month ago. for a bunch of teachers
in glitter, like you, Ancame up after the show.red
I thought he's going to tell me how good a show it was
and that he enjoyed it. He was furious with me.
He says, "My wife will never believe I wasn't
back in that strip club." ( laughter )
"Hey, not my fault, fella." So, yeah.
Now, on the subject of things burning in air.
I've got here some coffee creamer.
Coffee creamer
If I had a teaspoon, does not usually burn.
put this torch underneath, and I would put some of this in it,
Oh, I see Rachel we would see it doesn't burn.
She must be going rusfor a teaspoon.oom.
Should we wait for her
Let's wait for her. or sLet's see what else her?
we've got here. Oh, I know what we've got.
I need to see how much of this
I need some liquid nitrogen. we've got.
all-time things. This is one of my favorite
This is close to This is really cold.
the freezing point of water. about 200 degrees below
but it's not really. This looks like water,
This is the other four-fifths of the air to oxygen.
And we'll come back to burning that.
What I want to show you here
we get things nice and cold. is what happens when
we're getting a little bit Now, if you notice,
There's moisture in the air. of fog coming off here.
moisture. YoHollywood makes fogout
by putting this into warm water.
on the ground. Fog is just clouds
right now if it was cold enough Therup there right now.here
It isn't, which is amazing, here.
( laughter )
in my life as yesterday. I've never been so cold
our own personal cloud. But let'There we go.can get
Just for a little while,
Relative to we gethe liquid nitrogen,loud.
the air that I just put in there
I'm going to cool it down. is very, very warm.
when you cool them down? What do things usually do
That man remembers They shrink, yes.
( laughter ) the last time he went swimming.
Let's see if we can get this balloon to shrink
without losing too much of my liquid nitrogen.
That shrunk down pretty well. I'll toss that out there.
I've got another balloon here I want to shrink.
Let me see
Here we go. Now, the observant may notice
that this one really
as much as the first one did. I can get it to shrink down
some, but then if I toss it that way, it expands.
Come back to me,
Okay, thank you. I need you again.
What's in this one? Not airHelium, right.right?
There's really only one thing you can do if you've got
a balloon full of helium. As long as,
now I just learned this.
tell your kids this. This is really important,
from the balloon, the helium is safe to breathe.
The powder that they put in the balloons
to stop the sides of the
isn't good to breathe. balloon from sticking together
from party balloons Soyou've bought in a store.the
That'll have the powder in it.
we washed the inside of them out We took these balloons and
( in very high voice ) very well, so that I...
and make my voice go up. can indeed breath in the helium
is because sound travels Now the reason my voice goes up
And as I talk to you very fast in helium.
The helium is coming out more and more, what?
because it is less dense of my lungs, rising up,
I've got another gas than air.
It isn't air. It isn't helium.
It's sulfur hexafluoride. Very, very dense.
Notice how fast the balloon drops.
It turns out that sulfur hexafluoride, mostly used
to insulate switch gear and electrical apparatus.
But sulfur hexafluoride,
is also another gas bthat you can breathe safely.e
Now if helium, being low density
what's something that's very makes my voice go up,
( in very low voice ) high densiYes indeed, do to it?
it does make my voice go down.
I can sound like Darth Vader. Now there is a problem
with this stuff.
to make sure that I get the gas exchange going.
Because if I just stay quiet, this gas isn't
going to come out of my lungs,
being heavier than air. In fact, I'm going to do that
a couple of times.
I'm going to suffocate Because what?
out of my lungs. if I don't get the stuff
really well. So make sure that that comes out
I don't see Rachel. TheOh, I thought you'd goneis.
to the bar a couple doors down. But no, it's okay.
Coffee creamer. You'll believe me,
this doesn't usually burn.
If a little is good, But if I mix it with air--
Then I think I can make it burn. more is better.
we can make this burn. Let's see how well
Why? Yep!
through there, big surface area, Because when I blew it
and it could burn well. loWhen I go to schools andt
do the liquid nitrogen demos, I often get kids coming up
afterwards and saying to me,
And I have to tell them, "That is really cool stuff!"
it's very, very cold." "No, it's not cool,
very, very cold, Let's make some other things
But I always get the question, like that banana.
Oh, thank you. "Where can I buy that stuff?"
where they can buy it. And I tell kids
you've got to have But I also tell them if you do,
And I'm betting that this little dewar here--
Is there any left in there? A little.
Costs probably on the order of $200 or $300.
They say to me, "I can't afford $200 or $300.
I'll just go down there and I'll get them
to put some liquid nitrogen in a Pepsi bottle for me.
And I'll take it to school
And I have to tell the kids fthat only an idiot
would put liquid nitrogen in a Pepsi bottle!
That's okay, this is
so it should be fine. a BActually, of course,le,
the putting it in the bottle
The dangerous bit iis if you cap the bottle off.?
You really don't want to put liquid nitrogen
in a sealed container.
take this bottle over here, and we'll see why you don't
put it in a sealed container. The reason is what?
When the liquid nitrogen
the molecules get to be ten times further apart.
That's ten times this way,
and ten times this way. So that one cup of liquid
I just put in there is going to try and turn into
1,000 cups of gas.
of gas are not going to fit into that bottle anymore.s
Let me do a mini version
you don't put liquid nitrogen ofin a sealed container.y
Now in here, yeah,
We're going to get this cold I'm hoping is a dipper.
some liquid nitrogen. andWhile I do that dip
and get that nice and cold--
I want to show you something That's pretty much cold.
for quite some time. else I've been practicing now
into that block of solid wood, I intend to nail
using for a hammer, a banana. Don't make me use this!
( laughter )
to do this, so if you would, Now, I need absolute silence
( soft thud ) Apparently not that banana.
So I tell you what. Let me get a glove on my hand,
and we'll see if this other banana
will work better for me.
so that dipper is getting I'm goinnice and cold.up there
We'll see if
Uh-oh. we can nail this nail--
( tapping banana on table ) That's the frozen side. ide.
( hammering sound ) There, we've pretty much
nailed that nail all the way
( applause ) into the block of wood.
to putting liquid nitrogen Now, let's go back
You might think I'm being a little nonchalant here,
as to get my hands
But honest, I'm not. in this liquid nitrogen.
We'll put this in here. I'm beNotice it doesn'tnot to.
immediately turn into a gas.
If I lower this in here really gently and not spill it.
I can actually
Now if I do spill it... ( popping sound )his.
There we go.
You can keep that as a souvenir! Well caught!
That happens. Now, I said I was being real
careful about not getting that
I don't think we've got enough liquid nitrogen on my hands.
This flower is mostly water. left to freeze this flower.
even just a little, I'll show you what would happen
to my hands if I got them frozen this much, and
then hit them against something.
I wouldn't want that happening It shatters.
Okay, let us move on. I've got a shop vac here,
a means of making air move. When air moves, it gets to be...
( loud bang ) ( audience exclaims )
Yeah! That's why you don't
put liquid nitrogen in a sealed container!
Well, not a good idea at all. ( applause )
Okay, let me see if I can get air to move here
and be at low pressure. I'm not sure which of these...
( turns shop vac on ) ( turns shop vac off )
I'm going to put this ball
It won't be able to get out, in the stream of air.
is low pressure. because the stream of air
the air at the sides If it tries to move sideways,
that's at high pressure, that isn't moving,
the stream of air. will push it back into
( turns shop vac on ) There we are.
I can even turn it
( turns shop vac off ) from one side to the other.
consequences, and some practical applications.
Let me tell you of a few. It's not a real one,
but have you ever wondered why
on baseballs and softballs? I mean, we could obviously
make them these days, smooth, yet we don't.
Why not?
so that if you put a spin on it, We want the stitching there
around with it. You think what's going to happen
to a ball if it's moving through the air
as well as spinning.
a kick in the direction Thyou want it to go anyway.ing
So it gets faster.
encounters the air The air on the other side
They get in each other's way trying to get past the ball.
That side's at higher pressure, then,
so it pushes the ball sideways. This is why you can throw
a curve ball. We didn't realize
that we could do this until high-speed photography
showed the ball really does curve sideways.
I'm not talking about curving it up and down.
Obviously, gravity does that. If I throw this ball toward the
lady at the back of the room
I can pretty much get it to you with a curve up/down,g
but it won't curve sideways.
Now, on the other hand, if I throw this one
and I put a spin on it, we ought to get it
to curve sideways.
put a big enough spin on it I cjust by hand. and
But I can throw it and put a
Let's see. big enough spin on it with this.
I'll again throw it toward you, but you don't have to be ready
to catch it.
has to be ready to catch it. Somebody over there probably
That did that. Let's see.
If we've got another ball here, LI'm pretty sure.
Ooh, we've got another couple.
a good spin on this one. Okay, so let's see if we can get
If I throw it Yeand I put a backspin on it,e.
we ought to actually
So I'm going to try and skim this over your heads
and have it lift up toward the back of the room.
Now sometimes I miss
which is why we stopped using real baseballs for this demo.
( laughter )
before it went down. There, see it actually went up
That's the Bernoulli Effect. That's called what?
applications besides And it has some pretty neat
Watch. just softballs.
Curved on the top, Glider wings.
The air has to go further over flat on the bottom.
That generates about 20% the top, so it has to go faster.
to keep it off the ground. of the lift that the glider uses
Some people think that. Most of the lift comes from
the fact that the wings are angled upwards.
Air hits them,
Newton's third law says what? aTherefore the glider
must get pushed up. It's the same, I'll bet,
as you did as a kid when you
and did that put your hand out of a car,
And you do that and it pushes your hand down.
So let's see. This ought to just glide out.
There we go.
And this is so much nicer than a bunch of little kids.
Because that is usually-- By all means, throw it back.
That's usually
I throw a big glider out. And then just for the teachers,
I tell them that's a science
( laughter ) model of piranha feeding.
little kid in the audience Oh, yeah, because every
tears it apart. grabs tSee?lider,
Just generating an awful lot
( laughter ) of lift for you, isn't it?
to use the Bernoulli Effect. Anyway, that's not the best way
and you can tell by my voice, When that I talk funny.ntry,
And it's not just the helium. ( laughter )
It's because I'm British. When I came over here,
it was Halloween. And I found something out
immediately.
( laughter ) You people are crazy.
They don't soap windows and toilet paper--
Nice shot!
No, they're much too refined Toilet paper houses in England.
That's probably why they threw me out.
I thought that's pretty cool. I've got to try that.
So, I toilet papered
I took way too long. the neighbor's house.
I figured you've got I got caught.
Science to the rescue. to be able to do this quicker.
How can you toilet paper Bernoulli Effect.
( machine roars loudly ) a house?
before the whole roll comes off. I'm going to turn that off
so if you would-- But I ( laughter )show tomorrow,
Very carefully. Very carefully roll
that back up for me!
Okay, I've got two more ( ldemos left.
If you would. But these last two demos
really do involve a little bit of danger.
So one, we're going to move these tables so that
they're out of our way
anything down from them. and we're not knocking
why I teach physics. And then, I'm going to show you
show sometimes and they ask me, Peo"David, why do you teachthe
physics?
big money to do it?" Is it because they pay you
Oh, I must have some teachers in the audience laughing,
because you know full well, no, they do not pay me
big money to do it. After one show,
this one lady comes up. And I said, "No, I don't
do this for the money." She looks at me and she goes,
"Oh, you do it
( laughter ) for the children."
No! I don't do it for the children.
I do it for the toys! This is one of my favorite toys.
Bed of nails. I'm going to lie on this bed
of nails for you in a minute, once we put this down here.
Let me get it in the right place.
And when I do,
I have to take some precautions. I'm hoping I'll be okay.
when I lie here, One, I'm going to need a pillow
all over my bald head. because otherwise, I get marks
and join the dots together. "Oh, look, it's a giraffe."
No, it's not. But I'm going to give you
a piece of advice now.
Should you try something This is serious.
never lie on a bed of nail. ( laughter )urself,
Yeah, think about it
You do not want to lie for a minute.
You want lots of nails. When I lie on here,
about 160 nails are going to
which means that any one nail suppis only going to have toght,
push on me with about one pound.
with one pound doesn't hurt. And a nail pushing on me
with one pound, it pushes back on me with one pound.
That's Newton's third law,
It doesn't hurt. right?
Three pounds, still not hurting. Two pounds, doesn't hurt.
beginning to get uncomfortable. Five pounds--
Ow, five pounds is too much.
weighing five times I woulwhat I do right now, here
but still only be the same size.
probably not be a problem. But twice as much would
will you? So RacI'm going to liehere,
on the bed of nails.
my beginner's bed of nails, nails down on my chest,
and Rachel's going to stand up
You're going to help her on top of me.
Now if you decide to try this at home, do not sit down fast!
( laughter )
Again, it's okay. I willLie down. that.
If you would. Oh, got to get the pillow
in the right place. Put that bed of nails
up on my chest. There we go.
Keep it away from the chin. Hop up there, Rachel.
He'll help you
And there! keep your balance.
( applause ) This is not bad.
Never try to do that demo with Rosie O'Donnell.
( laughter )
the show, I told you about the Now you remember when I started
A big, heavy weight moving fast? demo we do with the pendulum?
I've got another big, heavy weight around here that we're
going to make move very fast. And I have a lot of energy.
I'm going to make this
What we're going to do with it, is we're going to break.
this brick. Now that doesn't seem
like anything unusual.
is going to be is-- I'm not lying on the bed
of nails, this good gent is.
on this bed of nails. We're going to put the other bed
of nails on top of him, put the concrete block on top,
smash the concrete block. Yeah.
Now before we do, just in case
"Oh, well, look how he's laying on that bed of nails.
It's not really sharp." Oh, yeah.
Oh, yeah, I'm betting when I pick this up,
yep, the entire bed of nails
I'm going to have to comes up with it.
( grunts ) put my feet on here.
that oh, yeah, those nails You can tell from that,
What this demo illustrates really were sharp.
of your car to crumple up if you're in an accident.
I'll bet there's a lot of you in the audience that remember
back when they made cars
You're in an accident, really strong.
They thought that was the the safe thing to doall.
to protect the people inside. And of course, it didn't protect
the people inside that much.
the car, but how fast are you Bgoing to stop the people?ed
What you want is for the impact to take longer.
You want all the energy,
the front of the car, tnot going into doing damageng
to the people.
what I want is for So when we break the block,
say, all of the energy all of the energy of the block,
to go into breaking the block, of the hammer,
goes into my friend here. Come over and give me a hand
laying him down on here.
safety gear on him first. WThe very first timee
that I did this demo
to wear eye protection. In fact, I'm going to
quickly dig in here and see if I've got some eye protection
for myself in here. Yep, I do.
I knew little bits of concrete
and go in my eyes. might come off
A piece of concrete the size of a golf ball came off
and hit me smack in the nose. Oh, that hurt!
So now, we put a face mask
I was so proud of thinking on him, as well.
the next time I did this demo. of the face mask
I put a face mask on. I I put my armsn.
in front of my face.
And I still got hurt. ThBut this man's not going to,.
because we're going to take even more precautions with him
than we took with me. Real gentle.
Don't get your feet on there. Come down and lay backwards.
There we go.
I'll put it there. Now we'll put this on top.
piece of equipment. Y( laughter )ecessary
Now you know how I got injured
( laughter ) the second time I did this!
on there too long, because this is worse than a Motel 6 bed.
I'm going to put this on. And let's see if we can do this
without hurting him.
Now quite a significant smash of the concrete block.
You can see why he needed the face mask.
And are you still living? Yeah? Good.
( applause )
Show these good folks your shirt.
See?
I hope you enjoyed it! That was my show, folks.
Thank you very much. ( applause )
Give this gent and yourselves Ya big round of applause..
Thank you very much. Well done, excellent.