# Machines

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Intro to Machines

Making work easier!
Machine
• A device that can change the magnitude
or direction of a force as it transmits
energy from a source to a target
Machines
Work In = Work Out
• Work on Bottle Opener
– Force applied to handle
– Handle moves because
of force
– Work is done
Machines
Work In = Work Out
• Work Done by Opener
– Force applied to bottle
cap
– Bottle cap moves
because of force
– Work is done
Machines
Work In = Work Out
W = F(Δx)            • If work must be equal,
what kind of
relationship between
force & distance?
– You move the bottle
opener farther than the
bottle opener moves the
cap.
– The force on the target
must be “increased” in
order to keep the work
equal!!
Machines
Some Important Terms

• Effort Distance: The distance YOU move the
machine
• Effort Force: The force YOU apply to the
machine
• Resistance Distance: The distance the
MACHINE moves the load
• Resistance Force: The force the MACHINE
applies to the load
Simple Machines
Inclined Plane
• Effort distance is
increased, which
reduces effort
force
Simple Machines
Screws
• A really long inclined plane
• The effort distance (the
path of the nut as it travels
“up” the screw) is
increased, so the effort
force (how hard you turn
the screwdriver) is
decreased
Simple Machines
Levers
• A solid object that is free to rotate around a
fixed point (fulcrum)
• Three different types of levers (1st class,2nd
class, 3rd class) depending on the location of
the effort force and the fulcrum
Simple Machines
1st Class Lever
Fulcrum between effort and resistance

Can make Fr bigger (if fulcrum is closer to target)
Can make dr bigger (if fulcrum closer to effort)
Simple Machines
2nd Class Lever
Resistance between effort and fulcrum

de is larger, but Fe is smaller
dr is smaller, but Fr is larger
Simple Machines
3rd Class Lever
Effort between resistance and fulcrum

de is very short, so Fe needs to be relatively large
dr is relatively large, so object on the end of lever moves more
Simple Machines
Pulleys
• Pulleys do not change
the force on the target
(they are basically a
tension force), but
they allow the force
applied by the source
to be applied in a
direction that allows
gravity to help.
Simple Machines
Multiple Pulleys
• Multiple pulleys add
more forces to load, so
the force is increased,
but the applied force
must be applied over a
longer distance
Simple Machines
Wheel and Axle
• Force applied to
wheel (wheel chair)
– Δxe is larger
(bigger wheel), so
Fe is smaller
– Δxr on axle is small
(smaller wheel),
so the Fr on axle is
large
Simple Machines
Wedge
• An inclined plane that
moves
• Fe applied to large end,
which is then
transferred to small
end, which moves a
relatively large distance
• Resistance distance (de,
material to be
separated) is relatively
small, but resistance
force (Fr) is large
How good could this machine be, theoretically?
Ideal Mechanical Advantage (IMA)
• Wo = Wi
• This relationship between
the distances moved (dr
de
IMA 
and de) is referred to as
Ideal Mechanical
• Under most conditions,              dr
IMA is determined by the
machine’s design, so…
How good is this machine really?
• In reality, how well a
machine transfers
energy can only be
Fr
determined by
comparing the effort
MA 
force and the                      Fe
resistance force
How good is this machine really?
• MA>1
machine will increase the force applied to
the target
• MA=1
machine does not change the amount of
force, just the direction of the force
• MA<1
machine applies a smaller force to target,
but distance moved will increase
What am I really getting for my money?
Efficiency (E)
• Any nonconservative forces that are involved
in an interaction will result in some
mechanical energy being converted into a
“non useful” form
• This reduces the amount of energy that is
transferred to the target
i.e The work done by the machine on the
target
What am I really getting for my money?
Efficiency (E)
• The percentage of
input work that is                   Wo
E       100%
transferred to output                Wi

work is called the
efficiency

MA
E      100%
IMA

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 views: 1 posted: 8/6/2012 language: English pages: 21
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