a

Gear Basics

a gear is similar to a pulley but it has

a series of teeth around the perimeter

of the wheel the teeth on two gears fit

together allowing one gear to turn the

other simple gears like these ones are

called spur gears their axles the bolts

through the center are parallel notice

that when I rotate the large gear

clockwise the small gear rotates the

other way counterclockwise gears can

change the direction of rotation gears

can also change the rate of rotation

let's rotate the large gear once and

count how many rotations the small gear

makes

did you get two rotating the large gear

once causes the smaller gear to rotate

twice the small gear also rotates twice

as fast as the big gear the big gear has

40 teeth how many teeth do you think the

small gear has remember that the small

gear turns twice as fast as the big one

if you estimated 20 you're right the big

gear has twice as many teeth as the

small one you can determine the rates of

rotation of two gears by comparing the

number of teeth on each one can you see

the different rates of rotation in these

gears the smaller gears rotate faster

than the big gears

spur gears are often joined on the same

axle creating a compound gear compound

gears provide even more options for

controlling rates of rotation some gears

are able to connect at an angle

these are bevel gears these bevel gears

are connected at a right angle or 90

degrees

gears can be used in machines to

increase force engineers call this

increase in force mechanical advantage

these machines usually have a small gear

driving a big gear machines using gears

control these locks locks are a special

system of gates located in a river or

canal system that are designed to move

boats up or down this system joins the

Ottawa River to the Rideau Canal and it

moves ships up or down a total of 24

metres the process is controlled by

human muscle assisted by a winch a hand

operated winch is a machine that

combines gears with a crank and chain

work able to create a large mechanical

advantage here's how these locks work a

boat moving from the Rideau Canal down

to the Ottawa River starts at the top it

is in a gated enclosure filled with

water the water flows out of this first

chamber until it is at the same level as

the next chamber at this point a winch

is used to open a huge pair of gates and

the boat moves into the next chamber

where the process repeats until it is at

the bottom and into the Ottawa River

this set of gears powered by human

muscle is moving the massive gate so the

boat can travel to the next level notice

a small gear is turning a big one

a ratio that provides a significant

mechanical advantage this machine

includes a crank and drum to wind the

chain onto these also increase the

mechanical advantage of this machine a

human without this machine could not

produce enough force to move the gates

gears make this possible

if you own a bicycle you have a machine

with a very sophisticated gear system

the gears on a bicycle don't mesh

directly like the gears we were looking

at a few minutes ago

these gears are connected by a chain

gears that are connected by a chain have

a special name they're called sprockets

we have a sprocket on the front here

that's connected to the pedals we have a

pedal arm we can create some force to

start moving that chain and on the back

we have another sprocket connected to

the rear wheel turning the pedals moves

the rear wheel you'll notice that the

pedals and the wheel move in the same

direction that's how a system like this

works with two sprockets in one chain

everything rotates in the same direction

some bicycles allow you to change gears

we know that if you use gears with

different numbers of teeth you can

change the rate of rotation

well this bicycle has three sprockets on

the front and five on the back giving

you a total of 15 different combinations

of gears that you can use here I've just

set this up so that I'm on the back

sprocket the one closest to me and I'm

on the back sprocket here at the back

wheel they both have exactly the same

number of teeth and when I rotate I'm

going to rotate the pedal all the way

around once we make one rotation of the

wheel with every rotation of the pedal

when the sprockets have the same number

of teeth here I'll just do that again

notice we've got our red marker here and

a pedal there I'll just rotate all the

way around to there

and we stop right there

the number of rotations are equal at

each end this gives you a good

mechanical advantage it makes it easier

to bicycle up hills for instance and get

started

bicycles are complicated there's also

also some mechanical advantage from the

pedals the length of the pedal arms the

size of your rear wheels and so on all

influenced the mechanical advantage here

let's change our gears for speed how to

do that we have some levers on the

handlebar that I can use to actually

move the chains

now I've moved our front chain it's on a

sprocket with 48 teeth and on the back

chain we're on a sprocket with 14 teeth

let's look at our rotations now I'll

line up the pedal and we've got our red

marker here and I'll start turning our

wheels gone once wheels gone twice three

times and when the pedals back to its

start position we've actually made about

three and a half revolutions with that

back wheel this gives us lots of speed

professional bicycle racers use

sophisticated gearing systems designed

to produce maximum power and speed gears

represent an ancient technology that we

continue to find new and exciting uses

for the gears in this sophisticated

robotic arm the Canada arm provide

precision control and significant

mechanical advantage orbiting the Earth

this powerful arm is being used to

construct the International Space

Station if you are teaching an

introductory unit on gears or just

interested in learning more about them

you may want to construct a gears

workstation to do this I purchased a bag

of gears from spectrum educational

supply in Newmarket Ontario similar

products are available from most science

supply retailers a 3/16 inch bolts works

well as an axle and properly spaced

holes drilled in a board allow you to

investigate various gear relationships I

also glued different sized gears

together to create compound gears

another good teaching tool is a clock

mechanism our video time clocks and

gears includes a demonstration with a

clock kit to view this video follow the

video link at our website highly rode

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