MACHINES and EFFICIENCY

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MACHINES and EFFICIENCY

• Chapter 9.8-9.9

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Key Terms

• Work Force x distance
• Simple machine
• a device used to multiply forces or change the
  direction of forces
• Compound machine
• A machine composed of two or more simple machines

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Key Terms

• Input (effort)
• Input distance the distance you input the force
  when using a machine
• Input force the force you use when using a
  machine
• Output (resistance)
• Output distance the distance the object that
  work is done on moves
• Output force the force required to move the
  object without a machine (usually the weight of
  the object in newtons)

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Key Terms

• Mechanical Advantage (MA)
• A unitless ratio that indicates the number of
  times a machine multiplies your input force
• Ideal Mechanical Advantage (IMA)
• The calculated MA, does not consider friction
• Actual Mechanical Advantage (AMA)
• The measured or real MA, does consider friction
• Because of friction, AMA lt IMA

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A simple machine

• Multiplies and redirects force
• Does not reduce the amount of work to be done,
  but makes work easier.
• MA gt 1 means that your input force will be less
  than your output force
• More leverage means more mechanical advantage
• If you increase MA, then
• Input force will decrease
• Input distance will increase

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Key Terms

• Efficiency (a ratio)
• Is calculated using the following equations
• Actual mechanical advantage/idealized mechanical
  advantage
• Useful work output/total work input

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Key Terms

• Efficiency of a machine decreases as friction
  increases
• Friction increases the thermal energy by
  increasing molecular KE (non-mechanical energy)
• In other words friction causes the particles to
  speed up, raising the average KE of the particles
  (and temperature!)
• Friction causes the useful work output to be less
  than the total work input

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Key Terms

• When using a machine
• Work is done to move the object
• Work is done against friction
• Useful work output is the work done to move the
  object
• Total work input is work done to move object
  work done against friction

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Simple Machines

• Two families

Lever
Inclined plane
--Lever --Pulley --Wheel and axle
--Ramp --Wedge --Screw
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LEVER FAMILY
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The Lever
fulcrum
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Three Classes of Levers

• First class

Examples Crowbar See-saw
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Three Classes of Lever

• Second class

Examples Wheelbarrow Door
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Three Classes of Lever

• Third class

Examples Human arm Baseball bat
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Calculating the Mechanical Advantage of a Lever

• MA input distance/output distance which isMA
  length of effort arm/length of resistance arm.

Effort or input distance
0.5 m
Resistance or output distance
2.5 m
Effort arm
Resistance arm
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Calculating the Mechanical Advantage of a Lever

• 2nd class lever
• 3rd class lever

2nd class levers decrease the input force but
increase the input distance.
3rd class levers reduce the output force, but
increase output distance and speed
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• Which lever would have the highest mechanical
  advantage and why?

b has the largest input distance, giving the
largest MA
c
b
a
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Pulley
Fixed pulley 1 support rope IMA 1
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Pulleys
IMA 2
Two supporting ropes
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Pulleys
IMA ?
2
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Pulley
How many support ropes?
4
What is the IMA?
4
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Wheel and Axle

• Wheel connected to a shaft

GIVES YOU LEVERAGE
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INCLINED PLANE FAMILY
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Inclined planes

• Ramps

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Wedge

• Two inclined planes stuck together

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Screw

• An inclined plane wrapped around a cylinder

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What type of machine is this?
Compound made of two or more machines
Two 1st class levers two wedges (scissor blades)