Machines

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Machines

• Machine A device which makes work
  easier.(Does NOT make less work)
• Machines change the size or direction or the
  applied (effort) force.
• Two forces involved with a machine.
  1. Effort ( FE ) or Applied force.
  2. Resistance ( FR ) or
  Force which object exerts on machine.

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Machines 2

• Work done by machine is work output. ( Wo )
• Wo ( FR ) ( dR )
• Work done on a machine is work input. ( WI )
• WI ( FE ) ( dE )
• In an ideal machine (no friction) WI Wo
• A machine does not make less work but it does
  multiply the applied force so that work is easier.

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Machines 3

• Mechanical Advantage (MA) is the number of times
  a machine multiplies the effort force.
• AMA ( FR ) / ( FE ) (Actual M.A.)
• Using 10 N of force to lift a 100 N object gives
  a M.A. 100 N / 10 N 10
• Sometimes M.A. will just equal one. In that case
  the machine usually changes the direction of the
  force.

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Machines 4

• Ideal Mechanical Advantage (IMA) is the distance
  in (effort distance) divided by the distance out
  (resistance distance).
• IMA ( ?din ) / (?dout ) (Ideal M.A.)
• If MA is less than ( lt ) one the machine
  increases distance or speed.
• Efficiency A comparison of WO to WI

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Machines 5

• Efficiency A comparison of WO to WI
• Eff. (WI / Wo) x 100
• High efficiency means that much of WI is changed
  to WO.

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Machines 6

• No machine is 100 efficient because there is
  always some effort force used to overcome
  friction.
• Lubrication (oiling, greasing) of a machine
  reduces friction and increases efficiency.
• A car engine is only about 20 efficient. The
  rest of the WI produces heat.

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7 Simple Machines

• Simple machines do work with one movement.

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8 Simple Machines 2

• Simple machines do work with one movement.
• Compound machines are combinations of two or more
  simple machines.
• 1. Inclined Plane2. Wedge3. Screw4. Levers5.
  Pulleys6. Wheel Axle

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9 Inclined Plane, Wedge

• 1. Inclined PlaneA slanted surface which gains
  height with length. The length you push or pull
  something is greater than the height.
• IMA Plane length / Plane height
• 2. WedgeAn inclined plane or double inclined
  plane that moves. Thinner at one end. Apply force
  at thicker end and he same amount of force is
  concentrated at the thin end.

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10 Wedge 2

• 2. WedgeAn inclined plane or double inclined
  plane that moves. Thinner at one end. Apply force
  at thicker end and he same amount of force is
  concentrated at the thin end.
• To improve MA of wedge you sharpen the thin edge
  (blade).
• Examples knives, ax, razor blade, tip of
  screwdriver.

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11 Screw

• 3. ScrewAn inclined plane wrapped around a
  cylinder. Rotates moves a certain distance with
  each turn.
• Multiples FE by acting through a long dE.
• MA increased by more threads per unit distance.

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12 Levers

• 4. LeversA bar which moves on a fixed pont
  called the fulcrum.
• First class lever. EFRexamples crowbar, pliers,
  scissors.
• Second class lever. FREexamples wheelbarrows,
  door, paper cutter.
• Third class lever. FERexamples hoe, shovel,
  fishing pole, fore-arm.

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13 Levers 2

• Third class lever. FERexamples hoe, shovel,
  fishing pole, fore-arm.
• Effort force is greater than resistance force but
  distance is multiplied.
• IMA effort arm length / resistance arm length.
• Pulleys Chain, belt, rope wrapped around a wheel.

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14 Levers 3

• 4. LeversA bar which moves on a fixed pont
  called the fulcrum.
• 1st Class EFR 2nd Class FRE 3rd Class
  FER

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15 Pulleys

• Pulleys Chain, belt, rope wrapped around a
  wheel.
• Movable Pulley Hung on a rope. Moves with effort
  force. Multiplies force. Does not change
  direction. IMA of supporting ropes.
• Fixed Pulley Attached to a stationary structure.
  Changes direction of force. Does not multiply
  force. IMA 1.

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16 Movable Pulleys

• Movable Pulley Hung on a rope. Moves with effort
  force. Multiplies force. Does not change
  direction. IMA of supporting ropes.

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17 Fixed Pulley

• Fixed Pulley Attached to a stationary structure.
  Changes direction of force. Does not multiply
  force. IMA 1.

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18 Wheel Axle

• Wheel Axle.
• A lever that rotates in a circle. Made up of two
  wheels of different sizes.
• Axle smaller wheel.
• Effort force applied to large wheel. Always
  through a greater distance than axle.
• Examples Bicycles, water wheels, gears.
• IMA Wheel radius/axle radius.

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19 Wheel Axle 2

• Wheel Axle.
• IMA Wheel radius/axle radius.