Mechanical Advantages of Simple Machines

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Mechanical Advantages of Simple Machines

• Science Overview on Simple Machines

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Three Classes of Levers

• First-class levers
• Second-class levers
• Third-class levers

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The Lever

• The principle of lever tells us that the above is
  in static equilibrium, with all forces balancing,
  if
• F1 x D1 F2 x D2

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A lever is a rigid bar that rotates around a
fixed point called a fulcrum. The bar may be
either straight or curved.
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First-Class Levers

• Examples
• Seesaw (also known as a teeter-totter)?
• Crowbar
• Pliers (double lever)?
• Scissors (double lever)

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Second-Class Levers

• Examples
• Wheelbarrow
• Nutcracker (double lever)?
• The handle of a pair of nail clippers
• Lemon Squeezer

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Third Class Levers

• Examples
• Human arm
• Tongs (double lever) (where hinged at one end,
  the style with a central pivot is first-class)
• The main body of a pair of nail clippers, in
  which the handle exerts the incoming force
• Oar (of the boat)

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6 Six Simple Machines

• Inclined plane (ramp)
• Wedge (axe)
• Screw
• Lever (can opener, see saw, tongs)
• Pulley (used in wells to draw water)
• Wheel and axle (door knob)

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How do we Calculate Mechanical Advantage of a
Lever?

• For the Lever
• MA length of effort arm length of
  resistance arm.

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MA of an Inclined Plane

• The mechanical advantage of an inclined plane is
  equal to the length of the slope divided by the
  height (aka rise) of the inclined plane. As an
  example, for the inclined plane illustrated
  above, assume that the length of the slope (S) is
  15 feet and the height (H) is 3 feet. The
  mechanical advantage would be

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MA of a Wedge

• The mechanical advantage of a wedge can be found
  by dividing the length of the slope (S) by the
  thickness (T) of the big end.
• Which of these wedges has the greatest mechanical
  advantage?
• Ans A is correct since A is "sharper",

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PULLEY

• A pulley is a wheel with a groove along its edge,
  for holding a rope or cable. Pulleys are usually
  used in sets designed to reduce the amount of
  force needed to lift a load.
• A fixed pulley has a fixed axle and is used to
  redirect the force in a rope (called a belt when
  it goes in a full circle).
• A fixed pulley has a mechanical advantage of 1.

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Pulley
A fixed pulley has a fixed axle and is used to
redirect the force in a rope A fixed pulley has
a MA 1. A single moveable pulley creates a
mechanical advantage however, it does not change
the direction of force.
A movable pulley has a free axle, and is used
to transform forces The mechanical advantage of
a moveable pulley is roughly equal to the number
of ropes that support the moveable pulley
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Movable Pulleys
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