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- I'm guessing that you've
had the experience of rubbing

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a balloon against your
hair and then when you take

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the balloon away from your
hair, your hair sticks up.

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And if you haven't had that experience,

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you might think about trying to lead

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a more rich and fun life,

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but I'm guessing most of
you all have done that.

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And you had a sense that it
had something to do with the

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balloon or your hair, somehow
exchanging charge or now

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one is going to be more positive
or negative than the other,

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and so now they are somehow attracted.

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And if you were thinking of those things,

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you are generally right.

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What you just experienced
after you rubbed the balloon

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on your head, and then
your hair is now attracted

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to the balloon, that's actually called

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the triboelectric effect,
let me write that down,

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tribo, triboelectric, electric effect.

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And human beings have been observing this

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for a long long time,
and it wasn't necessarily

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with balloons at birthday
parties or whatever,

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it's with other things, they
rub a silk cloth on a piece

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of glass and then they'll
see that there's some type

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of attraction, or they
might see that if they

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do that enough, one of the
objects might discharge

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when it touches another object.

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People have observed
things like lightning,

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where it looks like there's
some type of a buildup

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and some type of a potential
and then all of a sudden

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it discharges and you have
this lightning and then this

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thunder blast sound that happens too.

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So this is something
that humans have observed

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for a long long time, and
scientists or people with a,

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I guess you could say a
scientific mind have been trying

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to understand it for a long
long time, and trying to come up

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with a framework for what
exactly is happening.

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Well lucky for us, we now
have a framework for it

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that explains it quite well.

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And that framework for what is going on

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with that triboelectric effect,

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is a framework around charge.

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Is a framework that we
now have around charge.

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And this tells us, this way
of looking at the world,

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says look, there's some things

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that just have a property called charge.

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Some things have a positive charge,

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Some things have a positive
charge, and it's somewhat

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of an arbitrary name, we just
happen to call it positive.

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And some things have what we
say is an opposite charge,

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or a negative charge, a negative charge.

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We could have called
this the magenta charge,

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and this the green charge,
we could have called this

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the hippopotamus charge and
this the ostrich charge.

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And we could have said that
hippopotami, I believe plural

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for hippopotamus, they're
always attracted to ostriches,

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but they always repel other
hippopotami, and likewise.

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The like charges repel or like hippo...

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You get the general idea.

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But I'll stick to the words
that people are used to using.

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And so if we say something has a charge,

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say a positive charge,

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and something else has a negative charge,

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then in our framework
that we're setting up,

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these two things are going to attract.

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So opposite charges are going to attract,

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while like charges are going to repel.

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So if you have a positive charge,

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and you have a positive charge,

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these things are going to accelerate,

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are going to accelerate
away from each other.

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And that's not just true
for positive positive,

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that's also true for
negative and negative,

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these two things are going to repel

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because they are like charges.

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Now it's very interesting
to think about this

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because we are so used to
thinking in terms of charge,

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even you know if, especially
in kind of the world

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of electricity you have the
positive and negative terminal.

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You think of charging up
your phone or whatever else.

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That it seems like, we completely,
charge is just something

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that is fundamental about the universe,

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and that's true to some, that's true,

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but you'd have to appreciate
that these are arbitrary words

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and they're really just
to describe a property

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that we have observed in the world.

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And if you go down to the
atomic level, we can get to

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a fundamental level of where
the charge is happening.

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But once again, these are really models

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for our brain to describe,
these are frameworks and models

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for our brain to be able
to predict and describe

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what we observe in the world.

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But if we run with this model,

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we can imagine at the atomic scale,

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the nuclei of atoms are composed
of protons and neutrons.

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So if you have some
protons, and then you have

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00:04:20,375 --> 00:04:24,521
some neutrons, I'll do two of
each, you have some neutrons,

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and based on this framework,
protons have a positive charge.

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00:04:29,832 --> 00:04:31,408
Protons have a positive charge.

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00:04:31,408 --> 00:04:34,192
Now once again, this convention
of calling them positive

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00:04:34,192 --> 00:04:36,466
and putting a plus on it,
it's not like protons have

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a little plus sign
tattooed onto them somehow.

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We could have called
those, we could have said

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they have a red charge, or
we could have even said,

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00:04:44,147 --> 00:04:47,113
we wouldn't of had to
even use the word charge,

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00:04:47,113 --> 00:04:50,547
this is just a convention
that we have decided to use.

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And so we say protons have
positive charge and then,

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kind of buzzing around the
nucleus of an atom, you often,

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or usually, or often have electrons.

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Electrons have a lot less mass.

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Mass is another interesting thing.

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We associate mass as just,
oh this is just something

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that we get, we understand
it in our everyday life,

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but even mass, this is
just a property of objects,

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it's just a property of matter,

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and we feel like we understand
it because on our scales

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we understand notions of
things like weight and volume,

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but even mass can get quite exotic.

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But anyway, the whole
point of this video is

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not to talk about mass,
it's to talk about charge.

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But all of these things that
we talk about in physics,

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these are just properties
that will help us deal

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with these notions, these
behaviors in different frameworks.

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But anyway, let's get
back to this little atom

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that I was constructing.

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So this atom, let's say
it has two electrons,

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and obviously this is not drawn to scale,

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and each of these electrons
have a negative charge,

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and they're kind of jumping around here,

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buzzing around this nucleus of this atom.

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And the reason why, this
model, even going down

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to the atomic scale and thinking
in protons and electrons

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is interesting, is that it
allows us to start explaining

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what is happening in the
triboelectric effect.

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What is happening in the
triboelectric effect is when you

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rub that balloon on your
hair, because of the property

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of the balloon, the
material of the balloon,

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and the materials of your hair,

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when they come in contact and they rub,

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the balloon is grabbing
electrons from your hair.

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So the balloon is grabbing
electrons from your hair,

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and so it is getting
more negatively charged,

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it is getting more negatively charged,

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and your hair is getting
more positively charged,

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00:06:31,766 --> 00:06:34,975
or essentially it's lost these electrons.

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00:06:34,975 --> 00:06:39,975
And so when you put the
balloon now close to your hair,

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remember like charges repel each other,

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so the electrons in your
hair try to move away

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from these other electrons,
the negative charge tries to

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move away from the negative charge,

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00:06:51,494 --> 00:06:52,794
and I guess you could say that

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the tips of your hair will
then become more positive.

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Are more positive and
they will be attracted,

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and they will be attracted to the balloon.

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So we can think about
what's happening in terms

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00:07:05,410 --> 00:07:08,906
of transfer of electrons,
that's exactly what's happening.

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And so when you think
that way, it's like ok,

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we are scientists, this is a nice model,

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we can start to think about
what's happening here.

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This model actually explains
a whole ton of behavior

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that we've observed in the
universe, including things like,

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lightning and whatever else,
you know the static shock

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that you get when you
might touch a doorknob

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after rubbing your shoes along the carpet.

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But we like to start, we
like to quantify things,

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so we can start seeing how much they repel

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or how much they attract each other.

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And so the fundamental unit of charge,

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or one of the fundamental units of charge,

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or I guess you could say the
elementary unit of charge

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00:07:45,862 --> 00:07:48,626
is defined in terms of the charge

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of a proton or an electron.

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So the fundamental, or I
guess you could say the

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elementary unit of charge
is denoted by the letter e,

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and this is the charge of a proton,

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00:07:59,739 --> 00:08:04,739
this is e for elementary,
charge of proton.

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And the charge of an electron,
even though an electron has a

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00:08:07,317 --> 00:08:10,283
much, much, much, much
smaller mass than a proton,

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most of the mass of an atom is

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from the protons and the neutrons.

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00:08:14,753 --> 00:08:16,582
So an electron has a
much, much smaller mass

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00:08:16,582 --> 00:08:18,227
than the protons and the neutrons,

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but it has the same but
opposite charge as a proton.

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So sometimes the convention
is to write negative e,

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00:08:26,090 --> 00:08:28,508
or maybe even negative one
e, sometimes depending on

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whether you view this as a
kind of the actual charge

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00:08:30,966 --> 00:08:32,652
or whether you view this as a unit,

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but here I'll view this
as the actual charge.

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You could view negative e as the charge,

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as the charge of an electron.

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And something that has no charge,

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like a neutron, we say they're neutral,

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and actually that is why
they are called neutrons,

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because they are neutral,
they don't have charge.

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So that right over there, that
over there is, is a neutron.

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Now when we start to get
on kind of a larger scale,

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00:09:00,507 --> 00:09:02,559
not on a sub-atomic scale anymore,

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00:09:02,559 --> 00:09:06,297
talking about electrons and
protons, the unit of charge,

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00:09:06,297 --> 00:09:09,284
in general the unit of
charge that we typically use

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00:09:09,284 --> 00:09:13,815
is the coulomb, is the coulomb.

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00:09:13,815 --> 00:09:18,815
Coulomb, it's named for
Charles Augustin de Coulomb,

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00:09:18,894 --> 00:09:21,941
so if we're talking
about the guy, and he was

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00:09:21,941 --> 00:09:25,314
an 18th Century French physicist,
we would use capital C,

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00:09:25,314 --> 00:09:26,553
but if we're talking about the units,

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00:09:26,553 --> 00:09:31,553
we would use lowercase c,
the coulomb, the coulomb.

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00:09:31,836 --> 00:09:35,818
And the coulomb is
defined, so one coulomb,

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00:09:35,818 --> 00:09:38,567
let me write it right
over here, one coulomb

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00:09:38,567 --> 00:09:43,055
and it uses the abbreviation
uppercase C, is equal,

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00:09:43,055 --> 00:09:45,062
or I'll say approximately equal to,

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00:09:45,062 --> 00:09:48,210
we're going to round here,
it's approximately equal to

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00:09:48,210 --> 00:09:53,210
6.24, 6.24 times 10 to the
eighteenth e, or you could say,

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00:09:55,444 --> 00:09:58,329
in magnitude wise, it's
equal to the charge

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00:09:58,329 --> 00:10:02,250
of 6.24 times 10 to
the eighteenth protons,

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00:10:02,250 --> 00:10:03,773
or magnitude wise,

214
00:10:03,773 --> 00:10:05,397
it would be the opposite if
you're talking about electrons,

215
00:10:05,397 --> 00:10:10,174
it would be 6.24 times 10
to the eighteenth electrons.

216
00:10:10,174 --> 00:10:11,515
Now if you want to go
the other way around,

217
00:10:11,515 --> 00:10:14,055
what is the charge of, the
magnitude of the charge

218
00:10:14,055 --> 00:10:16,574
of say a proton in terms of coulombs,

219
00:10:16,574 --> 00:10:18,341
well you would just take
the inverse of this.

220
00:10:18,341 --> 00:10:23,341
So you could say that e
is approximately equal to

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00:10:24,030 --> 00:10:27,680
the inverse of this which is 1.60,

222
00:10:27,680 --> 00:10:29,390
I guess you could say
the reciprocal of this,

223
00:10:29,390 --> 00:10:34,390
1.60 times 10 to the negative 19,

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00:10:34,981 --> 00:10:38,658
times 10 to the negative 19 coulombs.

225
00:10:38,658 --> 00:10:40,670
So hopefully this gives
you an appreciation for,

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00:10:40,670 --> 00:10:42,702
I guess at a base level, what charge is.

227
00:10:42,702 --> 00:10:44,388
And in some ways it's like
it's this everyday thing,

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00:10:44,388 --> 00:10:46,237
you're used to it, we're used
to dealing with electricity

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00:10:46,237 --> 00:10:48,350
and we'll talk much more
about that in depth.

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00:10:48,350 --> 00:10:51,255
But at some levels it is this thing,

231
00:10:51,255 --> 00:10:52,494
one of the mysteries of the universe,

232
00:10:52,494 --> 00:10:55,704
how did these two particles
know to attract each other,

233
00:10:55,704 --> 00:10:56,761
you know it looks like
they're at a distance,

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00:10:56,761 --> 00:10:59,362
how do they immediately
exert a force on each other.

235
00:10:59,362 --> 00:11:02,103
how do these particles know
immediately to repel each other,

236
00:11:02,103 --> 00:11:03,689
it's not like they have
a wire connecting them

237
00:11:03,689 --> 00:11:05,233
that they're communicating somehow,

238
00:11:05,233 --> 00:11:07,850
or I guess once you get
to quantum mechanical,

239
00:11:07,850 --> 00:11:09,865
an argument can be made that
they are communicating somehow.

240
00:11:09,865 --> 00:11:11,670
But in our everyday,
kind of logical sense,

241
00:11:11,670 --> 00:11:12,941
it's like well at a distance,

242
00:11:12,941 --> 00:11:15,345
how do these things actually
know to repel or attract,

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00:11:15,345 --> 00:11:16,717
and what is this charge anyway?

244
00:11:16,717 --> 00:11:18,399
You know we've put all
these names around it

245
00:11:18,399 --> 00:11:21,202
but to kind of help us think
about it and have a framework

246
00:11:21,202 --> 00:11:22,401
and predict what will happen.

247
00:11:22,401 --> 00:11:26,017
But do we really know
what this charge thing is.

248
00:11:26,017 --> 00:11:28,171
So on one level it's kind
of plain and mundane,

249
00:11:28,171 --> 00:11:29,756
and it deals with balloons and hair,

250
00:11:29,756 --> 00:11:31,340
but on another level it's this deep thing

251
00:11:31,340 --> 00:11:35,932
about this universe, it's
a deep property of matter

252
00:11:35,932 --> 00:11:40,280
that we can manipulate and we
can predict, but it is still

253
00:11:40,280 --> 00:00:00,000
this very fundamental and
somewhat mysterious thing.