Simple Machines by xiuliliaofz


									Simple Machines
Matt Aufman and Steve Case
 University of Mississippi
       NSF NMGK-8
      February 2006
         Simple Machines
• Have few or no moving
• Make work easier
• Can be combined to
  create complex
• Six simple machines:
  Lever, Inclined Plane,
  Wheel and Axle, Screw,
  Wedge, Pulley

                NSF North Mississippi GK8
                 • A rigid board or rod
                   combined with a
                   fulcrum and effort
                 • By varying position
                   of load and fulcrum,
                   load can be lifted or
                   moved with less
                 • Trade off: must
                   move lever large
                   distance to move
                   load small distance
                 • There are 3 types of
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              1st Class Lever
• The fulcrum is
  located between
  the effort and the
• Direction of force
  always changes
• Examples are
  scissors, pliers,
  and crowbars

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           2nd Class Lever
• The resistance is
  located between
  the fulcrum and
  the effort
• Direction of force
  does not change
• Examples include
  bottle openers and

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                3rd Class Lever
• The effort is
  located between
  the fulcrum and
  the resistance
• Direction of force
  does not change,
  but a gain in
  speed always
• Examples include
  ice tongs, tweezers
  and shovels      NSF North Mississippi GK8
        Mechanical Advantage
• We know that a machine multiplies whatever
  force you put into it:
            - Using a screwdriver to turn a screw
            - Twisting a nail with pliers
            - Carrying a box up a ramp instead
            of stairs
• The amount that the machine multiplies that
  force is the mechanical advantage of the
• Abbreviated MA
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     Mechanical Advantage
• (IMA) Ideal MA: This is the MA of a
  machine in a world with no friction, and
  no force is lost anywhere
• (AMA) Actual MA: This is simply the MA
  of a machine in the world as we know it
             - Force is lost due to friction
             - Force is lost due to wind, etc.

• Can we have an ideal machine?

               NSF North Mississippi GK8
    Mechanical Advantage: Lever
• The mechanical
  advantage of a lever
  is the distance from
  the effort to the
  fulcrum divided by
  the distance from the
  fulcrum to the load

                          • Distance from effort to fulcrum:
• For our example,        10 feet
       MA = 10/5 = 2
                          • Distance from load to fulcrum:
                          5 feet
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Inclined Planes
                    • A slope or ramp that
                      goes from a lower to
                      higher level

                    • Makes work easier by
                      taking less force to
                      lift something a
                      certain distance

                    • Trade off: the
                      distance the load
                      must be moved would
                      be greater than
                      simply lifting it
                      straight up
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Mechanical Advantage: Inclined Plane
• The mechanical
  advantage of an
  inclined plane is the
  length of the slope
  divided by the height
  of the plane, if effort is
  applied parallel to the

• So for our plane                     • Let’s say S = 15 feet, H =
    MA = 15 feet/3 feet                3 feet
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Wheel and Axle
       • A larger circular wheel
         affixed to a smaller
         rigid rod at its center
       • Used to translate force
         across horizontal
         distances (wheels on a
         wagon) or to make
         rotations easier (a
       • Trade off: the wheel
         must be rotated
         through a greater
         distance than the axle

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Mechanical Advantage: Wheel and Axle
• The mechanical
  advantage of a wheel
  and axle system is
  the radius of the
  wheel divided by the
  radius of the axle

• So for our wheel and
  axle MA = 10”/2” = 5

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             • An inclined
               plane wrapped
               around a rod or
             • Used to lift
               materials or
               bind things

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    Mechanical Advantage: Screw
• The Mechanical
  advantage of a screw
  is the circumference
  of the screwdriver
  divided by the pitch
  of the screw
• The pitch of the
  screw is the number
  of threads per inch

•    So for our
    screwdriver                    Circumference = ∏ x 1” =
         MA = 3.14”/0.1”           3.14”
    = 31.4
                                   Pitch = 1/10” = 0.1”
                   NSF North Mississippi GK8
             • An inclined plane
               on its side
             • Used to cut or force
               material apart
             • Often used to split
               lumber, hold cars
               in place, or hold
               materials together

NSF North Mississippi GK8
Mechanical Advantage: Wedge
• Much like the
  inclined plane, the
  advantage of a wedge
  is the length of the
  slope divided by the
  width of the widest

• So for our wedge,
     MA = 6”/2” = 3
• They are one of the
  least efficient simple
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• A rope or chain free to
  turn around a
  suspended wheel
• By pulling down on the
  rope, a load can be
  lifted with less force
• Trade off: no real trade
  off here; the secret is
  that the pulley lets you
  work with gravity so
  you add the force of
  your own weight to the
                  NSF North Mississippi GK8
Mechanical Advantage: Pulley
• The Mechanical
  Advantage of a pulley
  is equal to the
  number of ropes
  supporting the pulley
• So for the pulley
  system shown there
  are 3 ropes
  supporting the
  bottom pulley
     MA = 3
• This means that if
  you pull with a force
  of 20 pounds you will
  lift an object weighing
  60 pounds
                  NSF North Mississippi GK8
       The trick is WORK
• Simple machines change the amount of
  force needed, but they do not change the
  amount of work done
• What is work?
   • Work equals force times distance
   • W=Fxd
• By increasing the distance, you can
  decrease the force and still do the same
  amount of work

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   Examples:                • Lever:
                                 • Work is equal on both
                                     sides of a lever. You
                                     move the long end a
                                     LARGE distance with
                                     SMALL force. The other
                                     end moves a SMALL
                                     distance with a LARGE
•Inclined Plane:                     force, which is why it
                                     can lift heavy objects.
   •It takes a certain amount of
   work to get the cabinet into the
   truck. You can either exert a
   LARGE force to lift it the
   SMALL distance into the truck,
   or you can exert a SMALL force
   to move it a LARGE distance
   along the ramp. NSF North Mississippi GK8
• The efficiency is a ratio that measures how much
  work the machine produces versus
  how much work goes in

• Example: We have an inclined plane
  with an ideal MA of 3. We measure
  our real-life inclined plane and find
  an MA of 2.
  Efficiency = Actual MA/Ideal MA x 100%
              = (2/3) X 100%
              = 66.66%
                       NSF North Mississippi GK8
                        Sources 2006. Simple Machines. Accessed 3 February 2006.
Jones, Larry. January 2006. Science by Jones: Levers. Accessed 2
February 2006. 2006. Simple Machines. Accessed 2 February 2006.
Professor Beaker’s Learning Labs. August 2004. Simple Machines:
inclined planes. Accessed 2 February 2006.
Wikepedia. Accessed 3 February 2006.

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