- Hey, I'm Diana.
You're watching "Physics Girl."
Back in my kitchen, and today we're going to make a mess.
I've got all kinds of ingredients ready
that are definitely not edible.
Let's get started.
Okay.
First experiment you should definitely try at home
is a prism made of Jell-O.
So I've got a laser pointer here,
and if I shine it through this Jell-O,
you can see some amazing optical properties of light.
So you can't see the laser beam
when it's outside of the Jell-O.
But as soon as I move it across the Jell-O,
you're seeing the laser beam
because of scattering of light.
The laser beam is scattering
off of the individual particles
inside the Jell-O and scattering
the light back to your eyes.
We can also see the property of reflection.
So you can see in the inside here
how the laser beam is reflecting
off of the inside surface of the Jell-O.
And if I get it at the right angle,
I can get a bunch of internal reflections.
You can actually also use this Jell-O like a prism.
So if you take it and put it in the sunlight,
it'll split the white sunlight up
into the colors of the spectrum.
I actually prefer the laser version, though.
You get to see so much more of what's going on.
You know my favorite fact about lasers?
They're the key tool used in detecting gravitational waves.
And if you don't know what gravitational waves are yet,
check the card up here.
Okay. Next experiment.
I'm going to open an aluminum soda can
using just a Sharpie.
But first, a quiz.
True or false?
A block of aluminum weighs 100 times more
than a block of steel the same size.
(hisses through teeth) Incorrect.
The answer is false.
It's only about three times less.
You must not have been peeling it today.
(laughs)
Too good.
Second question.
True or false?
Australia is the world's leading producer of aluminum.
And the answer is false.
I read that about Australia on a fact website,
and then I fact checked it and found out
the real answer is China.
Back to you, Diana.
Thank you, Diana.
Okay. Here's the experiment.
I'm going to need safety goggles for this one.
All right.
So you take your Sharpie and you hold it really firmly
in your hand and you press it against
the lip of the soda can.
It's got that little groove right there,
so you want to go back and forth,
pressing firmly along there.
And eventually what happens if you do that is...
(loud pop) - Whoa!
- Whew! Aah!
What was science? I've forgotten.
It scared it right out of me.
See how on this pull tab of a soda can
there's a little groove there?
Right there the aluminum is thinner,
so the material is a little bit weaker there.
And as we rub the Sharpie back and forth across the lip,
what you're doing is
you're flexing the metal back and forth.
And metals have this property where typically if you bend
them back and forth like that,
they fatigue and they get weaker and weaker.
So eventually that little groove part gets so weak
that it can't hold in the pressure of the can.
Cause these cans are pressurized to over atmosphere.
Actually, two to three times atmospheric pressure.
That pressure's all pushing out,
eventually it pushes out so hard
on that little weak joint
and it pops it right open
Okay.
On to the next experiment,
which also has to do with materials.
I'm going to poke this skewer all the way
through this balloon.
What happens usually when you poke with the skewer?
(loud pop)
Aah! It pops.
Before we go on, though,
here's a little trivia quiz about stretchy materials.
For stretchiest materials in the world,
what is the farthest we've been able to stretch them
so that they still recover their original shape?
Is it A, twice their original length,
B, 10 times their original length,
or C, 50 times their original length?
We'll come back to the quiz in a second,
but first we're going to learn how to skewer a balloon.
You need to find the magic spots in the balloon.
So take a look through the balloon at a light.
You can see through the sides,
but you can't see through the bottom part near the tie
or the top part.
That's because these parts are thicker.
Just in case.
So I go through the bottom,
and I like to twist it a little bit.
I even pinch it a little bit
so that it gets even less stretched.
Ooh!
Well, we're definitely through,
cause I heard a little air leaking out.
And
(loud pop) Oh no!
Try this again.
(loud pop)
Uh-oh.
(balloon inflating)
Aah!
It went through.
(gasps)
And that's how you skewer a balloon.
You know, I've seen people do this before,
but something that I've never seen anyone try before
is to stick the skewer through the sides of a balloon
and try to blow it up with the skewer already inside.
(loud pop)
(laughs)
It very quickly pops.
But if you stick the skewer through the top,
through that nubbin, it works.
That's because it's easier to tear or rip or break
the thinner parts of the balloon.
Just like it's easier to tear one page of a book
rather than the entire book.
Okay. Back to the answer to the quiz.
For the stretchiest materials in the world,
what is the farthest we've been able to stretch them
so that they still recover their original shape?
Drum roll.
And the answer is C.
There are materials like
elastomeric polysiloxane nanocomposites
that have elongations of over 5,000 %.
That means that if you took some of this material,
a foot in length,
you could stretch it to over 50 feet
and it would come back to the same shape.
That's insane.
It would be like blowing up one of these balloons
to over a six foot diameter.
We actually tried blowing up the balloons
as far as we could earlier.
And we only got them to about two feet.
(loud pop) Ooh!
Orange, you glad you know that now?
The next experiment involves a balloon and a candle.
Adult supervision required for this one.
Hold the balloon over the candle,
and it will...
(loud pop) (screams)
Dude, it put the candle right out.
Fun fact about candles.
In the 18th century,
many lamps and candles were made from spermaceti,
which is the oil collected from
the head cavity of a sperm whale,
which also led to the near extinction
of those majestic creatures.
Anyway, if you use a balloon with some water in it,
there's only a little bit of water,
but if I hold it above the candle now...
If this pops, water is going everywhere.
But I am getting it right on that candle flame.
Second fun fact.
Water can hold 11 times
as much heat as gallium.
What that means is if you apply the same amount of heat
to the same mass of water in gallium,
the gallium will heat up 10 times faster.
So the water in this balloon is sucking up all the heat,
but temperature is not increasing that much.
Oh, dear.
Aah!
Next experiment.
We have to go into a dark room.
I've got a bunch of Band-Aids in here.
When you rip open Band-Aid wrappers, they glow.
This is so cool.
It's a process called triboluminescence
where the process of ripping apart the wrappers
strips charges off of
the material in the wrappers
and electrons fly across the air
and release light.
It's totally visible.
You have to let your eyes adjust for awhile in the dark,
and it works best with certain brands of wrappers,
but it's so cool.
It just wastes all your Band-Aids.
For the next one,
we're going to do a really cool experiment
with milk and food coloring,
but I've got a twist on this one.
The traditional experiment goes like this.
You take some milk, put it on a plate,
then take a little bit of food coloring,
put it in the middle of the milk.
Okay.
Now take a Q-tip, dip it in some dish soap,
put that right in the center of the food coloring.
Ooh!
You get some really, really cool patterns
if you keep the soap in there.
Now, this is typically done with milk,
but I wanted to try it with water.
Okay.
So I'm gonna pour some water on the plate,
I'm gonna drop some food coloring in here,
and I have to move quickly because
it's gonna diffuse fast.
So I've got my soap in here
and I'm going to go ahead and
dip it right in the middle.
Ooh!
So it works, but it's different
because the water moves out
in an almost perfect circle.
Whereas with the milk,
it moves out in this diamond shape.
And I actually don't know why.
If I can figure out the physics before this video goes up,
I will share it with you.
But otherwise, I'm gonna leave that mystery to you.
You can also show the same effect with water and pepper.
So I'm gonna put some water in the plate,
sprinkle in some pepper
all over the surface of the water.
Now I'm going to dip the Q-tip in the soap again.
So cool.
So the reason that this happens is because
water has got this surface tension.
It's like springs.
All the molecules are pulling against each other.
When you put soap on the top,
soap has these molecules that have
hydrophobic and hydrophilic ends.
Hydrophobic, meaning it's scared of water,
Hydrophilic, meaning it likes water.
So the hydrophilic ends stick down toward the water.
They're all orienting themselves that way.
They're also spreading out over the surface
because soap is less dense than water.
So it sits on the surface.
So the water is pulling like these springs,
and it's almost like you're sticking springs
in the middle that are weaker,
because soap has a weaker surface tension than water.
So the water is pulling out and it pulls the soap,
which doesn't hold on as strong,
And it pulls the pepper along with it.
Now, this doesn't just work with soap.
If there's some other substance
that is less dense than water
and will spread over the top of the water
in a thin film and has
a lower surface tension than water,
this should work.
Can you think of anything that fits those criteria?
I tried oil.
Let's check it out.
So I'm actually gonna use oregano this time
because this pepper has a little bit of oil in it,
so it already affects the surface tension.
I'm just going to sprinkle some oregano
and then dip my Q-tip in
and touch that to the surface.
So the soap is a lot more effective with this experiment,
but the corn oil definitely works.
I can actually see the edge of the corn oil film,
where it's reached to the edge of this oregano here.
Science is awesome.
Thank you so much for watching.
I hope you try some of these experiments at home.
And happy physics-ing.
Would you like to phone a bunch of friends?
You still have the option to ask the audience.
Have you ever been to Australia?
Oh, you were born there, huh?
Pear.
Now I'm gonna...
Can you quit yammering away?
Come on. I'm rooting for you.
Get it? It's the root vegetable.
(hums Jeopardy theme)
(laughs) (ladle clattering)
Mic drop.
(upbeat music)