♪♪
(Emily Dunlop)
 Nice, aren't they?
We harnessed electricity at the
beginning of the 20th century
so that we could create
lights like these,
here at the
Botanical Gardens,
in Atlanta.
But the force behind
 this amazing display
began when the
 universe was created.
Until a few hundred
 years ago,
people thought electricity
 was just a curiosity.
Now, just think
 about all the ways
in which we
 depend on it.
What exactly is it?
And how does it all work?
We're going to answer
these questions
in this segment of
"Physics in Motion"
on electricity.
Let's put electricity
 into a bigger picture.
Look up there.
Electricity is part of one
 of the four fundamental
forces at work
 in the universe.
They dictate much of what
 happens among matter.
Interactions among these force
 fields make everything happen.
Electricity is one part
of the fundamental force
called electromagnetism.
You can guess what
the other one is.
We'll talk more about
magnetism later in this unit.
But electricity and magnetism
are very closely related.
Different parts of
the same phenomenon.
How does electromagnetism
plug in with the other forces?
In ascending order
of strength,
the forces are, gravity,
 being the weakest.
Next, is what scientists
 call the weak nuclear force,
which operates at
 the subatomic level,
regulating
 radioactive decay.
The second strongest is
 our topic, electromagnetism.
It governs how electrons
 and protons interact,
and binds the electron
 cloud to the nucleus.
And the strongest of all is
called the strong nuclear force.
It operates at the
 subatomic level,
like the weak force does,
keeping protons and neutrons
 together within the nucleus.
To give you an idea of
 the range of strength
we're talking about,
the strong nuclear force is
 about a hundred times stronger
than the
 electromagnetic force
and about a million
 times stronger
than the weak
 nuclear force.
Now that we
understand more about
the fundamental force
of electromagnetism,
let's look at one
of its components.
Electricity.
We've all felt it.
This is one form that
electricity takes.
We usually call it
static electricity.
But, more precisely,
it's a static electric shock.
We feel the shock
when electric charges
that have been stationary
move suddenly.
That's called static
electric discharge.
But static electricity
doesn't always occur
on a small scale.
This, for instance,
is also static
 electric discharge.
(lightning crashing)
Whether it's monumental
 or just a household annoyance,
static electric charge
can build up on an object
and create a jolt
as it leaves.
But what exactly
is happening
that creates the
electrostatic force?
Here's how these
particles interact.
A positively
 charged proton
and a negatively
 charged electron
attract each other.
Electrons repel each other,
 and so do protons.
That's the rule,
which you've probably
 heard in other contexts.
Opposite charges attract,
 and like charges repel.
And just like gravitational
force pulls harder
the more mass
an object has,
the strength of
electrostatic force
depends on the amount of the
electric charge on an object.
Put another way.
The more charge
an object has,
the stronger the force it exerts
on the other charged objects.
But there's a key difference
between the way gravity
and the electrostatic
force works.
Gravity only works
one way, it pulls.
That's because mass only
 comes in positive amounts.
You can't have
 a mass less than 0.
Electric charges, though,
 can be positive or negative.
They can both pull when
 the charges are opposite
and push when the
 charges are alike.
And how do these
 particles act?
Protons don't move
 from atom to atom
because they're very tightly
 bound in the nucleus.
Electrons, however,
 are in the electron cloud
around the nucleus.
And because they're
 farther away,
the atom holds them
 more loosely.
So, they can move
 from atom to atom.
If a neutral atom
 gains an electron,
that atom becomes
 negatively charged.
If it leaves, the atom
 becomes positively charged.
It's the electrostatic force
that causes the movement.
And the more
electrons involved,
the more charge you have,
and, therefore,
the stronger the force.
Just like gravity,
the electrostatic
force depends on
the inverse square of the
distance between objects.
As the distance between the
 two charge points increases,
the force decreases.
That may seem
 kind of obvious,
but when a guy named
 Coulomb figured that out
almost 300
 years ago,
it was a gigantic leap
 in our understanding
of how electricity works.
Coulomb's discoveries made it
possible to harness electricity,
which, as we all know,
is a very big deal.
But back to how the
electrostatic force behaves.
Sometimes, when the
electrostatic force
acts on a charge,
it is counteracted
by other forces,
and the charge doesn't
move very much.
In other cases, though,
the force does put
the charge in motion.
When that happens,
with untold trillions
of charges,
we get something we all
use every single day
called current
electricity.
We call it that because
it's a collection of charges
that flow, like a river,
through a circuit.
Georg Ohm studied the
 flow of electric current
and found that it was related
 to the difference in potential
between two wells of charge,
known as voltage,
and the resistance
that charge encounters
within a given path.
Ohm's law allows us to
 harness electricity
into circuits that allow us
 to light our homes,
power our computers,
and generally make
 modern life possible.
When a circuit is closed,
 the current is dynamic,
always on the move.
Though the charges
 move randomly
at nearly the
 speed of light,
they progress slowly
 through a circuit.
In fact, it takes them a
 few hours to move a meter.
So, why do all of
 these lights come on
as soon as we
 flip the switch?
Though the current
 flows slowly,
the electric field that
 drives it does not.
It goes into effect
 throughout the whole
length of the wire at
 almost the speed of light.
Though the electrons also
 move at a very high speed,
they're not moving in
a constant direction.
They move almost randomly,
colliding with atoms,
and generally behaving
like bumper cars.
But, still, the general
direction is moving forward,
and that's why we
 can use the charges
to do so many things.
We've talked about the
four fundamental forces
in the universe,
and focused on one aspect of
the electromagnetic force,
electricity.
We've seen how this
amazing force is created
by the subatomic particle,
electrons,
and how the forces of
attraction and repulsion
can cause them to move.
We've also learned that
electricity can take two forms.
static and current.
And we've seen the roles
each plays in our daily lives,
resulting in an amazing
display like this.
That's it for this segment
of "Physics in Motion".
We'll see you guys
next time.
For more practice problems,
 lab activities,
and note-taking guides,
check out the
 "Physics in Motion" toolkit.
