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Machines
What do a saW and a computer have
in common? Both are machines. one
is simple and the other very complex,
but both are tools that do work for us.
Machines perform tasks that we would
find difficult or even impossible to do.
You cannot cut through wood with your
bare hands, for example, but it is easy
with a saw. Likewise, a computer can do
calculations rapidly that would take you an
enormous amount of time. all machines need
a source of energy. Mechanical machines,
such as a corkscrew, use the energy of
movement. a motor or a person’s muscles
drive the machine with a certain amount of
force called the effort. the machine then
applies this movement but produces a larger
force to move a load. For example, your fingers
operate a can opener, but the blade of the can
opener moves with much more force than that
produced by your fingers. Many hand-powered
machines help us perform tasks for which we do
not have enough strength. they use devices
known as simple machines. these include
levers, gears, pulleys, and screws.IncLIned PLane
simple machines reduce the
effort needed to move or lift an
object, but the object has to travel
a greater distance. the simplest
machine is the ramp, or inclined
plane. You need less force to push
an object with a downward load
up an inclined plane than you
need to lift it straight up. this
is because the object moves a
greater distance along the plane.
the gentler the slope, the
farther you have to push,
but the easier it is.Archimedes’ screw (above) is an
ancient device for raising water. As it
turns, the screw shifts water along its
thread instead of moving itself forward.screW
a screw moves forward a
shorter distance than it
turns. It therefore moves
forward with a much
greater force than the
effort needed to turn it.
the screw bites into the
wood with great force
and is held strongly.PLoW
the plow has
a cutting blade that
bites into the soil
and a V-shaped
blade that turns
the soil over.PerPetual motion
Many inventors have tried to
build a machine that, once started,
would never stop. It would run
on its own without any source
of energy. however, such a
perpetual motion machine is
impossible. this is because all
machines lose some energy as
they work. Without a constant
source of energy, a machine
always slows down and stops.The screw makes
use of the principle
of the inclined plane.The thread of the screw
is like a slope wrapped
around a cylinder.Wedge
the wedge is a form of inclined
plane. Instead of moving a load
along a slope, the wedge is
a slope that pushes a load
aside or upward as it moves
forward. the wedge
pushes with greater
force than the effort
needed to move the
wedge. sharp blades
are thin wedges that
make cutting
an easy task.LoadGentle slope—
Steep slope— small effort
large effortEffortForceAx is a kind
of wedgeIn this machine, the motion of the balls
was supposed to keep the wheel turning.EffortForceForceLoadForceUS_327_Machines_1.indd 327 22/01/16 11:11 am