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Work and Simple Machines
A
machine is a tool used to make work easier. Simple
machines are simple tools used to make work easier.
Compound machines have two or more simple machines
working together to make work easier. In science,
work is defined as a force acting on an object to
move it across a distance. Pushing, pulling, and lifting
are common forms of work. Furniture movers do work
when they move boxes. Gardeners do work when they
pull weeds. Children do work when they go up and down
on a see-saw. Machines make their work easier. The
furniture movers use a ramp to slide boxes into a
truck. The gardeners use a hand shovel to help break
through the weeds. The children use a see-saw to go
up and down. The ramp, the shovel, and the see-saw
are simple machines.
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Inclined
Plane
A plane is a flat surface. For example, a smooth board
is a plane. Now, if the plane is lying flat on the ground,
it isn't likely to help you do work. However, when that
plane is inclined, or slanted, it can help you move
objects across distances. And, that's work! A common
inclined plane is a ramp. Lifting a heavy box onto a
loading dock is much easier if you slide the box up
a ramp--a simple machine. |
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Wedge
Instead of using the smooth side of the inclined plane,
you can also use the pointed edges to do other kinds
of work. For example, you can use the edge to push things
apart. Then, the inclined plane is a wedge. So, a wedge
is actually a kind of inclined plane. An axeblade is
a wedge. Think of the edge of the blade. It's the edge
of a smooth slanted surface. That's a wedge! |
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Screw
Now, take an inclined plane and wrap it around a cylinder.
Its sharp edge becomes another simple tool: the screw.
Put a metal screw beside a ramp and it's kind of hard
to see the similarities, but the screw is actually just
another kind of inclined plane. How does the screw help
you do work? Every turn of a metal screw helps you move
a piece of metal through a wooden space. And, that's
how we build things! |
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Lever
Try pulling a really stubborn weed out of the ground.
You know, a deep, persistent weed that seems to have
taken over your flowerbed. Using just your bare hands,
it might be difficult or even painful. With a tool,
like a hand shovel, however, you should win the battle.
Any tool that pries something loose is a lever. A lever
is an arm that "pivots" (or turns) against a "fulcrum"
(or point). Think of the claw end of a hammer that you
use to pry nails loose. It's a lever. It's a curved
arm that rests against a point on a surface. As you
rotate the curved arm, it pries the nail loose from
the surface. And that's hard work! |
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Wheel
and Axle
The rotation of the lever against a point pries objects
loose. That rotation motion can also do other kinds
of work. Another kind of lever, the wheel and axle,
moves objects across distances. The wheel, the round
end, turns the axle, the cylindrical post, causing movement.
On a wagon, for example, the bucket rests on top of
the axle. As the wheel rotates the axle, the wagon moves.
Now, place your pet dog in the bucket, and you can easily
move him around the yard. On a truck, for example, the
cargo hold rests on top of several axles. As the wheels
rotate the axles, the truck moves. You can move your
dog across the country! |
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Pulley
Instead of an axle, the wheel could also rotate a rope
or cord. This variation of the wheel and axle is the
pulley. In a pulley, a cord wraps around a wheel. As
the wheel rotates, the cord moves in either direction.
Now, attach a hook to the cord, and you can use the
wheel's rotation to raise and lower objects. On a flagpole,
for example, a rope is attached to a pulley. On the
rope, there are usually two hooks. The cord rotates
around the pulley and lowers the hooks where you can
attach the flag. Then, rotate the cord and the flag
raises high on the pole. |
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If
two or more simple machines work together as one,
they form a compound machine. Most of the machines
we use today are compound machines, created by combining
several simple machines. Can you think of creative
ways to combine simple machines to make work easier?
Think about it.
source:
http://www.fi.edu/qa97/spotlight3/spotlight3.html
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