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Machines
Lever, wheel and axle, gear, wedge, inclined plane, and pulley.
Pulley
A pulley makes it easier to lift
something straight up. It consists
of a piece of rope wound around
a wheel. One end of the rope is
attached to the load and force is
applied to the other end to pull
up the load. When a pulley has
more than one wheel the pulling
force is increased.
Inclined plane
It is easier to push or pull something up a slope than
lift it straight up. A slope, or inclined plane, therefore
increases force. In ancient Egypt, stones were dragged
up slopes to build the pyramids.
Screw
A screw is a machine. It is really
an inclined plane, or slope, going
round and up. A corkscrew uses
a screw. It is easier to twist the
point of a screw into a cork than
to push a spike straight in.
Wedge
An axe blade
is an efficient
but simple machine
that increases force.
When it hits
the wood, the
wedge forces
the wood to split
apart between
its fibres.
The screw turns around a
greater distance than it moves
into the cork, so it moves into
the cork with more force than
is used to turn it.
The crane lifts
up heavy loads
with a system
of pulleys.
It takes just one man to pull
a stone up the slope, but
four men are needed to lift
a stone straight up.
