English subtitles for clip: File:0762 Spinning Levers 04 45 20 00 3mb.webm

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[fanfare]

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[fanfare fades]

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Meet Mr. Archimedes of Ancient Greece.

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Long ago, Archi said,

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"Give me a lever long enough,

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and I can move the world."

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What Archimedes meant was that the
power of a lever is practically unlimited.

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Today, almost everyone uses
some form of lever in his daily work.

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The familiar can opener is a
lever with a sharp cutting edge.

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The playground seesaw
is just a simple lever too.

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It takes a lot of force to
start a freight car moving,

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yet the railroad man can start the heaviest
freight cars easily with a pinch bar,

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a powerful lever which turns the wheel.

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Just like old boy, here's a place
where a lever comes in mighty handy.

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Let's take the simplest kind of lever:

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a rigid bar working on a
fixed support called a fulcrum.

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One end of this lever is
twice as long as the other.

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Let's put a ten-pound
weight on this end,

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and now we'll put half as
much weight on this end.

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Five pounds balance ten.

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If we have twenty-five pounds
to lift, we just use a longer lever.

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The five pounds will now
balance five times as much.

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Let's raise the lever in the air,

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change its shape a little,
and we have a crank.

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Or we add a second lever
and have a double crank.

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Now the short arm moves
one-fourth the distance,

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but we get four times the force.

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If we want continuous
motion, we need more arms.

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Now we have levers that turn.

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The larger paddle
wheel makes fewer turns

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but it delivers more force.

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A paddle wheel is nothing but
a never-ending series of levers.

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We can make the wheels stronger

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and lessen friction where
the wheels touch each other

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by rounding off the edges
and shaping them into teeth

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that will slide in and out smoothly.

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Now, the power flows
smoothly and continuously

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through spinning
leverage of gear wheels.

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Gears are made in many
kinds and many sizes –

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little gears, big gears,

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worm gears, bevel gears

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and even lopsided gears.

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Over a hundred million gears
are spinning over the roads

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in the transmissions
of our automobiles.

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The transmission is located right
at the bottom of the gear shift lever.

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Let's start from scratch
and put together a model

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of the gears that we
shift in our motor car.

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The shaft on the left
comes from the engine.

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The shaft on the right carries
the power back to the rear wheels.

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To connect these two with gears,

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we'll need another shaft
known as a countershaft.

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These two gears carry the power
from the engine shaft to the countershaft,

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and are always connected or in mesh.

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This gear on the drive
shaft going to the wheels

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is free to turn around the shaft.

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We'll put it in mesh with
another gear on the countershaft.

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These gears are always in mesh...

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and keep turning while
the engine is running.

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To switch from one
set of gears to another,

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our transmission needs
a short shaft like this,

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known as a clutch sleeve.

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It cannot turn on the drive shaft,
but it is free to slide back and forth.

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On the sleeve, we'll note a large gear,

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which we can shift back
and forth to mesh with

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the small gear in the
middle of the countershaft.

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We are now in neutral.

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The gears that are always in mesh
are turning over with the engine,

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but the shaft to the rear
wheels is standing still.

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A three-thousand-pound
automobile takes a lot of force to start.

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So in low speed, we
get the greatest leverage

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by letting the smallest
gear on the countershaft

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turn the largest gear
on the drive shaft.

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The engine on this model is
running at a constant speed

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of ninety revolutions a minute.

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With low gears in mesh, the rear wheel
is turning at thirty revolutions a minute,

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about a third the speed of the
engine, but with three times the force.

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The power is going through
these gears in the transmission.

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After we've started the car
rolling, we want fast pickup,

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so we shift into second by
sliding the sleeve backward

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to mesh with this gear on
the shaft to the rear wheels.

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The wheel is now turning
at sixty revolutions a minute,

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and the power flows
through these gears.

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For higher speeds, we let the
power go directly to the rear wheels

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We shift the sleeve forward

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so that it meshes with
the shaft from the engine.

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The power travels straight
from the engine to the drive shaft.

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Now the shaft to
the wheels is turning

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at ninety revolutions a minute:

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the same speed as the engine.

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But here's a problem:

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an automobile must be able to
go backward as well as forward,

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so we add one
more set of gears to

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reverse the shaft
to the rear wheels.

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With the gears shifted into reverse,

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the power travels through the
transmission in a path like this.

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We now have three sets of
spinning levers for going forward,

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and one for reverse.

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With a gear shift lever, we can
shift to any set of gears we wish.

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But with all these spinning levers in
the transmission came noise and wear.

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Experts could shift
gears quietly by careful timing

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of the gear shift
and the engine speeds,

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[gears screech]
but most of us made plenty of noise

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until new engineering
developments made possible

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a long series of
improvements that followed.

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When we shifted
gears, we got a clash

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because the gears were not
running at the same speed –

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in other words, not synchronized.

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So engineers set to work
to develop a synchronizer.

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The synchronizer works like a
cork twisted into the top of a bottle.

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The cork will turn until it is so
tight that the bottle turns with it.

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Synchromesh works the same way.

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When we shift into second or high,

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the synchronizer brings the gears to the
same speed before they come together.

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The drums won't let the gears shift
unless they are turning at the same speed.

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When the gears come
together, there is no clash,

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and the shift is made
quietly and easily.

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In the transmission of
the up-to-date automobile,

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we have a powerful low gear to give
us a strong spinning leverage in starting.

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A fast-turning motor must set
the weight of the car in motion.

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In second speed, we can
change leverage to get going fast

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at the same engine speed.

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With the leverage of third gear,
power goes directly to the rear wheels

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and we can go as fast as we want.

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Now every driver can shift gears
at any time, regardless of speed.

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Here is a hill that will give us a
real chance to see how smoothly

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and reliably our spinning levers
work in our automobile transmission.

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This driver is going to let her car gain a
speed of sixty miles an hour down the hill.

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[same fanfare as before plays]

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Then she will shift into second
speed and bring her car easily

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and safely under control before
it reaches the bottom of the hill.

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[fanfare continues]

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[fanfare finalies]