Simple Machines2008
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Simple Machines2008 Presentation Transcript

  • 1. Simple Machines May 9, 2008
  • 2. Objectives
    • Explain how a machine makes work easier
    • Calculate mechanical advantage
    • Describe an ideal machine
    • Explain why machines are not 100% efficient
  • 3. History of Work
    • Before engines and motors were invented, people had to do things like lifting or pushing heavy loads by hand. Using an animal could help, but what they really needed were some clever ways to either make work easier or faster.
  • 4. Simple Machines
    • Ancient people invented simple machines that would help them overcome resistive forces and allow them to do the desired work against those forces.
  • 5.
    • Machines make work easier by changing the size and/or the direction of the force
      • In order for work to be done:
        • A force must be exerted
        • There must be movement in direction of the force
    • The two most common resistive forces are friction and gravity
    Machines
  • 6. Machines make work easier by changing
    • the amount of force you exert
    • the distance over which you exert your force
    • the direction over which you exert your force
  • 7. Simple Machines
      • a device that does work with only one movement
  • 8. Types of Simple Machines
    • inclined plane
    • wedge
    • lever
    • wheel & axle
    • screw
    • pulley
    These make work easier !
  • 9.
    • when using a machine to do work
      • Effort (Input) Force (F E ) – This is the force you apply to the machine
      • Resistance (Output) Force (F R ) – This is the force that the machine applies
    2 general forces involved
  • 10.
    • Work In (W in ) – The work done on the machine (energy put into the machine)
    • Work Out (W out ) – The work done by the machine (energy put out by the machine)
    2 types of work involved
  • 11.
      • W in = F e x D e
      • W out = F r x D r
  • 12. Mechanical Advantage
    • The number of times a machine increases a force exerted on it
    • MA = output force / input force
  • 13. Mechanical Advantage
    • When the output force is greater than the input force, the MA is greater than 1 .
    • If you exert an input force of 10 N on a can opener, and the can opener exerts an output force of 30 N, the can opener has a MA of 3.
  • 14. Mechanical Advantage
    • For a machine that increases distance, the output force is less than the input force. So the MA is less than 1 .
    • If you exert an input force of 20 N and the machine’s output force is 10 N, the MA is 0.5
    • The machine only exerts half of your force but it is exerted over a loner distance.
  • 15. Mechanical Advantage
    • If only the direction changes, the input force will be the same as the output force. The MA will always be 1 .
  • 16. Efficiency
    • Compares the output work to the input work.
    • Efficiency = W out x 100%
    • W in
    • The higher the percent, the more efficient the machine.
  • 17.
    • one in which there is no friction, no energy is lost so work in and work out would be equal
      • W in =W out F e x D e = F r x D r
    • In reality, work out will always be less than work in because energy is lost through friction
    Ideal machine