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So where I had left off
is we had the circuit.

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We had these little
leads here.

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This was kind of
our innovation.

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And this is actually called a
commutator, where this part

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that's connected to our rotating
piece, that's the

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commutator.

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And these are the brushes.

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So you could imagine, you could
design them as brushes

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that always stay in touch.

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Kind of like the brushes
on a, what was that?

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What are those cars at
the amusement park?

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Bumper cars, right?

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On the bumper cars you have a
pole behind your bumper car.

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I'll draw that for fun.

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So let's say this is
your bumper car.

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Looks like a shoe
a little bit.

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This is you driving
your bumper car.

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And they have a pole.

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And at the top of the pole,
you'll see these brushes that

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are touching the
ceiling, right?

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You could view that as the
same type of brush.

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And what it allows is a constant
electric current to

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flow through the ceiling.

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I don't know what direction
it's going in.

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But it allows a current to
flow through the ceiling.

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And maybe your car is grounded
so the current can flow down

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to ground, so that your car
could be powered by the

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ceiling and not have to carry
a battery in every car.

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Which would be kind of a waste
of energy and probably some

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type of a health hazard
and safety risk,

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et cetera, et cetera.

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So those brushes on your bumper
cars might not be all

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that different from the brushes
that are touching the

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commutators here.

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Just a little bit
of terminology.

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And it never hurts to
introduce bumper car

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references.

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I probably should have done
them earlier when we were

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learning about momentum
and things.

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But anyway.

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So what was happening here?

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So going back to our
first video.

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We have the current going
down like this.

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And then if you use your right
hand rule with the cross

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product, you know that the net
force from the magnetic field

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is going to be downwards on the
left hand side, upward on

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the right hand side.

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So you have a net torque
rotating it like that.

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Rotating the right out of the
page, the left into the page

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or into the video screen.

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Up to the point that you've
rotated 90 degrees and now

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you're looking kind of, so
this side right here.

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Let me do it in a different
color so you can see it.

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This side is this side,
right on top.

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And this side is on the bottom,
below the page.

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This side is now
above the page.

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If this distance is r,
this side is now r

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units above the page.

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And I said ideally maybe your
commutator loses touch with

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the brushes at this
point, right?

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Because they're popping out a
little bit, so when you're

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vertical, you actually lose
touch with the brushes.

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So you have no circuit flowing,
so you save a little

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battery energy.

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And you just let a little bit of
the angular momentum carry

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this whole rotating contraption
further a little

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bit to the point that
your configuration

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will look like this.

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So I know I keep changing
colors, but the whole

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contraption will now
look like this.

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OK, that's my positive,
negative, positive, negative,

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current flows like this.

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Now we assume that the
commutator has

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gotten back in touch.

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And let me color code this.

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So if this side is this
color, right?

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Now this is when we're looking
at top on, where it's popping

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out of the screen, where
it's above the screen.

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And now we've rotated 180
degrees and this side is on

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this side, right?

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Let me pick a suitable color.

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If this side was green.

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Now this side, we flip the whole
thing over 180 degrees.

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And now something interesting
happens.

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Remember, before we had this
commutator and everything, if

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we just flipped it over, the
current, because before when

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we didn't have the commutator,
the current here was flowing

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down here, up here.

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And before the commutator, we
had the current flowing down

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here and up here.

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And so we were switching
directions.

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And so you would have had this
thing that would never

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completely rotate.

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It would just keep flipping
over, right?

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Which may be useful for, I don't
know, if you wanted to

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flip things.

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But it's not useful
as a motor.

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So what happens here?

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Now this side, all of a sudden
instead of being connected to

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this lead, is now connected
to this lead.

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And this green side is now
connected to this lead.

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So something interesting
happens.

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Now the current on the left side
is still flowing down,

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right, and the current
on the right side is

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still flowing up.

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So we're back to this
configuration except that this

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contraption has flipped over.

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The brown side is now on the
left and the green side is now

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on the right.

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And what that allows is that
those net torques are still

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going in that same rotational
direction.

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Use your right hand rule.

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The current is flowing
down here.

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So if your magnetic field is
coming to the left, then the

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net force is going to be
down there and it's

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going to be up there.

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And so we can continue
indefinite, and we solve our

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other problem.

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That we will never keep twisting
these wires here.

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So now using the commutator, we
have essentially created an

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electric motor.

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And remember I drew that little
thing, that could be

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like the axle.

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Maybe that turns the wheels
or something.

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So if you have a constant
magnetic field and you just by

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using this commutator which,
as soon as you get to that

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00:05:04,120 --> 00:05:07,300
kind of vertical point, it cuts
the current, and then

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00:05:07,300 --> 00:05:10,060
when you go a little bit past
vertical, a little bit past 90

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00:05:10,060 --> 00:05:13,190
degrees, it switches the
direction of the current.

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So on the left hand side you
always have the current coming

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down, and on the right hand
side you always have the

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00:05:17,840 --> 00:05:18,720
current going up.

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So that the net torque is always
going to be pushing, is

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always going to be rotating this
contraption down on the

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left hand side and up on
the right hand side.

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Coming out of the page on the
right hand side and then down

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00:05:34,040 --> 00:05:34,990
on the left hand side.

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And you could actually
turn a wheel now.

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00:05:37,730 --> 00:05:39,400
You could create an
electric car.

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So that is the basics
really of how

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electric motors are created.

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00:05:45,150 --> 00:05:46,190
Well, there's another way
you could have done it.

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You didn't have to use
the commutator.

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00:05:47,320 --> 00:05:51,100
One methodology you could have
used is you could have had the

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magnetic field going until you
get to this point, and then

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00:05:54,650 --> 00:05:56,770
you turn off the magnetic
field, right?

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00:05:56,770 --> 00:06:02,150
And maybe you wait for this
situation to go all the way

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00:06:02,150 --> 00:06:05,060
180 degrees and then you turn
the magnetic field back on

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00:06:05,060 --> 00:06:06,130
again, right?

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00:06:06,130 --> 00:06:07,550
That's one possibility.

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00:06:07,550 --> 00:06:10,460
But that's maybe not as
efficient cause half of the

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00:06:10,460 --> 00:06:11,910
cycle you're not powering it.

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00:06:11,910 --> 00:06:13,325
Or maybe you switch
the direction of

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the magnetic field.

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00:06:14,310 --> 00:06:16,240
Or another option, you don't
have to use a commutator.

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Maybe you use some other
contraption to switch the

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00:06:17,890 --> 00:06:19,160
direction of the
magnetic field.

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00:06:19,160 --> 00:06:21,030
But this is probably the
simplest way to do it.

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And I think it gives you a
general idea of how an

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00:06:24,010 --> 00:06:25,480
electric motor can be created.

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00:06:25,480 --> 00:06:28,460
And then we could play around
with the mechanics of

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00:06:28,460 --> 00:06:29,230
innovations on it.

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00:06:29,230 --> 00:06:32,500
But all electric motors are
essentially some variation of

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00:06:32,500 --> 00:06:35,020
what you have learned
in this video.

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Isn't it neat to learn
something useful?

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See you in the next video.

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