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(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.