Simple Machines

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Chapter 6

• Simple Machines

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Simple Machines

• Wedge
• Cam
• Screw
• Lever
• Pulley
• Wheel Axle
• Hydraulic press

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Black Box Machine

• Use input force to do work
• Ideal Machine input work equals to output work
  (no losses)
• We can change the amount of force needed to do
  the work

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Inclined plane

• Pushing a box up inclined plane with incline
  angle ? (no friction)
• Lift straight up
• Using inclined plane
• Hence reduced force needed
• But

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How to characterize Machine?

• Ideal Mechanical Advantage
• Geometrical construction
• Ratio of output force to input force for ideal
  machine
• Can get IMA of 30-100 or more
• Jack chain hoist

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Back to Inclined plane

• Pushing a box up inclined plane with incline
  angle ? (no friction)
• Lift straight up
• Using inclined plane
• Hence reduced force needed
• But

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Actual Mechanical Advantage

• Energy losses in machine
• Define AMA

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Efficiency of Machine

• How good is a given machine?
• In terms of power

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ExamplePulley Systems

• 20 kg load can be lifted with 65 N force. Pulling
  rope 150 cm lifts load 30 cm. Find IMA, AMA, Eff?

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More simple machines

• Wedge
• Screw Jack (cam r, pitch p)
• Lever (Fulcrum)
• Pulley
• Hydraulic press

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Example

• If it takes 100 ft-lb of torque to tighten an
  engine bolt. How long should the wrench be if 60
  lb of force is applied?

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More on Pulley Systems

• IMA of a block and tackle equals to the number of
  strands supporting the moving block.

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ExamplePulley Systems

• 20 kg load can be lifted with 65 N force. Pulling
  rope 150 cm lifts load 30 cm. Find IMA, AMA, Eff?
• How many strand?

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Example

• A pulley can lift 5000 N using 1000 N force. If
  the IMA is 20, what is the efficiency of the
  system?

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Hydraulic Press

• Volume fixed (cross-section area A)
• IMA
• Almost no losses

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Example

• Compressed air furnishes a force of 60 N to the
  0.8 cm2 area of an oil line that is used to lift
  a piston in a car lift. What must be the cross
  sectional area to be able to lift 1100kg vehicle?

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Combining machines

• Machines in series
• Output of 1st is the input of 2nd, etc.
• Break 2x2