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.
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.
Want to know more? Here's
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! Want to know more?
Here's extra information.
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.
Try this demonstration to help you
visualize. 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!
Want to know more? Here's
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!
||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.
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.
|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.
- For more information about simple machines, try browsing these
- The Elements of Machines: Simple Machines
- Exploring Leonardo Homepage
- Simple Machines Activities