Simple Machines

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Simple Machines

• Making Life Easier

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Working on the Railroad???
Q. What does working on the railroad have to do
with Simple Machines?
A. Early railroad workers had little to work
with. Often they used simple wooden poles wedged
tightly against a rock to push the heavy iron
rails into place.
The poles were a type of simple machine. Simple
machines make work easier to do.
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LEVERS
A LEVER is one of the simplest of simple
machines. You balance a stick on an object
called the fulcrum. If the stick on either side
of the fulcrum has the same length, the stick
will give you no advantage - it will not make the
work of lifting an object any easier. If the end
of the stick you push down on is longer than the
end under the heavy object, you will be able to
easily lift the object.
The trick?
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How Levers Work
Notice in the drawing that the arrow representing
the Effort force is much longer than the arrow
representing Resistance force. This means that
you are moving that end of the lever a greater
distance in order to raise the heavy object a
smaller distance. Your effort force is
multiplied by moving the effort arm (the end of
the lever you push down on) of the lever a
greater distance.
Effort Force
Resistance Force
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Levers In Daily Life
Many people use levers to make their work
easier. A shovel is a lever with the heel being
the fulcrum. A can opener contains a lever to
amplify the force of your hand to break a hole in
the lid of the can. Many machines, including car
engines contain levers that amplify the force of
the machine to do the intended work of the
machine. All these common devices contain levers.
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How Many Levers Do You See?
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Inclined Planes
The bulldozer (or snowplow) being used in the
picture on the last slide is a good example of
another kind of simple machine, the Inclined
Plane. An inclined plane amplifies the lifting
ability of the person using it.
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Inclined Planes
Have you ever tried to lift a very heavy object?
Did you ever wonder if there was an easier way?
Using an inclined plane, you get an advantage by
pushing the heavy object a long distance up a
slight incline in order to lift it up to the
height you require.
Effort Force
Resistance Force
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How Inclined Planes Were Used
How Our Ancestors Used Inclined Planes
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How Were the Ancient Pyramids Built?
Modern archeologists and stone masons have
studied the ancient Egyptian and Mayan pyramids.
These were built over 5,000 years ago out of huge
limestone blocks weighing many tons by people who
had no machines to move them or lift
them. Actually they did have several machines,
simple machines. One method was to build a very
long incline out of dirt that rose upward to the
top of the pyramid very very gently. The blocks
of stone were placed on large logs (another type
of simple machine - the wheel and axle) and
pushed slowly up the long, gentle inclined plane
to the top of the pyramid.
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Modern Pyramids
Some modern home-builders are designing (see
drawing at left, top) and building houses in
pyramid shape. They find that this gives them a
lot of living space at an economical price.
Commercial builders are finding that pyramids
give them a lot of space for the cost. Among
many examples of modern pyramids is the Luxor
hotel in Las Vegas that is higher than many
skyscrapers!
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The Wheel and Axle
Hi! I am Og! I invented the wheel. This was
one of the first simple machines!
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Wheel and Axle
We take the wheel and axle for granted. Its
main use is in transportation. It makes moving
from place to place a lot less work. This is why
a wheel and axle is a simple machine.
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Wheel and Axle
Wheels were probably invented first. Later,
someone had the bright idea of threading an axle
through the wheel and discovered a simple
machine. When the wheel is firmly attached to
the axle, you can get an advantage by turning the
much larger wheel. In turn, the wheel turns the
smaller axle. In this way, you can twist open
something that is too hard to turn directly like
the rudder of a ship!.
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Pulleys
Although a pulley is a separate simple machine,
all it is really is a set of wheels and axles
combined to get a better advantage.
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Pulleys and Mechanical Advantage
Mechanical Advantage is what you get out of a
simple machine to make work easier. In most
simple machines, you get mechanical advantage by
moving something a longer distance. For example,
you turn a larger wheel a greater distance to
move the smaller axle a shorter distance. Without
the larger wheel, the smaller axle might be
impossible to turn! With one pulley and one
string, there is no mechanical advantagethe
force you put into pulling on one rope, is the
force that comes out the other end!
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One-Pulley System
Notice that it takes 5 lbs of force to raise the
5 lb mass. This is a mechanical advantage of 1
which is no advantage.
5
5 lb
Spring scale
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Two-Pulley System
Notice that it only takes half the force (2.5
lbs) to lift the 5 lb weight. This pulley system
has a mechanical advantage of 2 which means that
for every pound of force you put into the pulley,
you get two pounds of lifting force out of
it. Once, a crane used a 12 pulley system to
lift a 10 ton safe out of a suburban garage. The
extra pulleys amplified the lifting force of the
crane eleven times!
2½
5 lb
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Screw
Some people would argue about including the
screw as a simple machine. True, it does give
you mechanical advantage, it shape making it
easier to insert it into a piece of wood.
Others argue that the screw is simply an
inclined plane wrapped around an axle. In other
words, it already is a simple machine - an
inclined plane.
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Wedge
The wedge is the active twin of the inclined
plane. It does useful work by moving. In
contrast, the inclined plane always remains
stationary. This simple machine consists of a
pair of inclined planes set face-to-face, that
can slide past each other. By moving one plane
past another, a wedge is capable of building up
enormous force in a direction perpendicular to
that of the moving wedge. Force multiplication
varies inversely with the size of the wedge
angle this means a sharp wedge ( small inclined
angle ) yields a large force. With adequate
friction at the
surfaces, the wedge becomes a
device that
separates, holds, or
stops something.

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Something for Nothing?
We have studied the different kinds of simple
machines. Each gives us mechanical advantage.
By using the simple machine, we somehow amplify
the force we put into the machine.
Where does this amplified force come from?
In order to get more force out of a simple
machine, we sacrifice distance. In other words,
we move one end of a lever farther than the end
that does the heavy lifting. In a pulley, we
pull the rope twice as far as the heavy object is
lifting.
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The End!