Simple Machines

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Simple Machines
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Machines
Machines help us accomplish tasks by changing the
direction or magnitude of a force that we
apply. Each object on the right is a machine of
some kind.
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Simple machines
There are six basic simple machines. These six
can be grouped into levers and inclined
planes.
Most other machines are made of some combination
or variation of these.
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Levers

• A lever is a simple machine that changes the
  magnitude of a force.
• The fulcrum is the pivot point about which the
  system is in rotational equilibrium.
• The input arm is the distance between the fulcrum
  and input force.
• The output arm is the distance between the
  fulcrum and the output (or reaction) force.

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Classes of levers
There are three classes of levers.
Third class levers have the input force in the
center.
Second class levers have the output force in the
center.
First class levers have the fulcrum in the center.
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Pulleys and ropes
A pulley is a simple machine that can change the
direction of a force.
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Pulleys and ropes
Combinations of pulleys can be used to change the
magnitude of a force as well as its direction. A
combination of pulleys is called a block and
tackle system.
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Wheel and axle
A wheel and axle provide a mechanical
advantage. Compare this wheel and axle to the
lever system.
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A ramp is a simple machine
When the Egyptians built the pyramids, they may
have moved the blocks up ramps constructed along
the side of the pyramid. How would using a ramp
make their job easier? Would they use less
force? Would they do less work?
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Trading force for distance
It takes a fixed amount of work to lift a
dresser to a certain height. Lift straight
up The upward forces equal the weight, and the
lift distance is small. Use a ramp Less force
is needed but the pushing distance is greater.
F2
F1
d
mg
FN
F
d
mg
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Wedges
A wedge is a simple machine that consists of two
inclined planes. Wedges have many uses.
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Screws
A screw is another example of a simple machine
that uses the same principle as an inclined
plane. The key property of a screw is its
pitch p, which is the vertical distance between
each successive thread.
p