Sky
ABOVE
How Simple Machines Work
Earth
Simple machines
include the lever, inclined plane, wedge, screw, pulley, gears, and the
wheel and axle. Some of them are variations on others; for example,
the screw is an inclined plane wrapped around a cylinder.
Though simple, they are powerful, and very useful. The key to simple
machines is a trade-off: force for distance. When using a simple
machine, you may have to push or pull further (more distance), but you
won’t have to push or pull as hard (less force). Think about the inclined
plane or ramp. Pulling something up a ramp, you’ll have to travel further
than if you went straight up (more distance), but you won’t have to pull
as hard (less force.) Sometimes, the simple machines can be used in
reverse: push harder over a shorter distance.
Did you know?
Simple machines are found everywhere.
Wedges: scissors, key, plow, zipper
Levers: hammer, baseball bat, wheelbarrow,
scissors, piano, bicycle brakes
Wheel + axle: steering wheel, faucet,
wind turbine, dental drill
Gears: car engine, windshield wipers
Pulleys: Elevator, escalator, crane
Screw: faucet, power drill, meat grinder
Find It In The News
BELOW
FUN TO DO
Simple machines are everywhere. One way to test them: break out the tools!
Safety note: Kids, get help from an adult science partner. Always be careful
using tools, and try these experiments in a place where a bit of a mess is
okay (i.e., not in the living room).
Some things you can use:
Claw-ended hammer, nails, screws, scrap pieces of wooden board, wooden
wedge (a door stop works well), Velcro, screwdrivers (at least some should
be flat-ended), an empty paint can, a rubber mallet, metal or PVC pipe,
flat-ended metal dowel or peg, pliers
Some experiments you could try:
1) Leverage: With levers, size matters. Use a hammer or mallet to tightly hammer shut a paint can (preferably an empty one!) Then try to pry
open the lid with a flat ended screwdriver --- start with the smallest
one you have. Start by pushing gently. Then re-hammer it on and try again, using a much longer screwdriver. (You could lengthen the small screwdriver by putting some pipe over the handle.)
2) Try a type of inclined plane: the wedge. Take two blocks of wood, and
use Velcro to stick them to each other. Try pulling them apart with your hands. Then use a wedge – put the point of a wooden door stop
between the boards and tap it with a hammer.
3) More levers: Hammer a nail halfway into a board. Grab it with pliers and
try to pull it out. Now try using the claw end of a hammer to extract it.
4) The pointy end of a nail is a wedge. Try hammering one into a board.
Then try hammering in a flat ended device (like a piece of metal dowel).
5) Turn of the screw: Hammer a nail halfway into a board. Then screw a screw halfway in. Try extracting both with the claw end of the hammer,
as you did in experiment #3.
6) Attach two boards together with nails, and two other boards using
screws. Try separating them with a wedge, like in experiment #2.
Could you feel the differences that different simple machines made?
With the lever in experiment #1, it’s easier to open the can with a screwdriver
(a.k.a., a lever) that is longer. If you measure, you see that with the longer
lever it means you push down further (greater distance), but you don’t
have to push as hard as with a short lever. This increased ease is called
mechanical advantage. Using the claw end of a hammer as a lever gives
you a mechanical advantage when pulling out a nail.
As long as the lever is strong enough, and it rests on something
(called a fulcrum) strong enough, there’s no limit to mechanical advantage.
A long enough, strong enough lever would let you easily lift a tractor trailer.
A screw creates extra friction with the wood, so it holds the boards in
experiment #6 together better than the nail.
Look at the list of items above, or look up more simple
machine devices. How many appear in newspaper stories?
Learn More
• Go to howtosmile.org and search “simple machines” for lots more experiments
• David MacAulay’s book “The Way Things Work” shows how simple
machines and lots of other machines function
For students who are blind, learning disabled or print challenged,
visit CRIS Radio at http://www.crisradio.org and click Kids On-Demand
for a free audio version of Geography Connections.
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