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Work, Power, and Machines

Work, Power, and Machines. Physical Science Chapter 12. Machines. devices that change the direction of a force or the size of a force that help us to do work machines will multiply your force OR change the direction of your force BUT CANNOT DO BOTH (can’t do work for you).

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Work, Power, and Machines

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  1. Work, Power, and Machines Physical Science Chapter 12

  2. Machines • devices that change the direction of a force or the size of a force that help us to do work • machines will multiply your force OR change the direction of your force • BUT CANNOT DO BOTH (can’t do work for you)

  3. 2 forces involved in the use of a machine: • effort force (input)- force applied to the machine • resistance force (output) force opposing the effort force • often equal to weight of object work input is ALWAYS > work output WHY? friction

  4. simple machine- machine that has only 1 or 2 parts • 6 simple machines: • lever- bar that pivots, or turns, on a fixed point 3 parts: a. effort arm- (input)- end of the bar you push on b. resistance arm (output)- end of bar that pushes on object you want to move c. fulcrum- point at which it pivots

  5. 3 classes of levers: A. first class lever-effort arm on one side, resistance arm on other, fulcrum in middle ex: see saw

  6. B. Second class lever: • fulcrum is at one end, EA at the other, RA in the middle • ex: wheelbarrow

  7. C. Third class lever • fulcrum at one end, RA at the other, and EA in the middle • ex: tweezers, forearm

  8. 2. Wheel and Axle • consists of a lever connected to a shaft • lever usually shaped like a knob or wheel • effort arm- radius of wheel • resistance arm- radius of axle to be considered W&A, BOTH wheel and axle MUST move

  9. 3. Pulley • consists of a wheel FREE TO SPIN on its axle • lever rotates around a FIXED POINT • 2 FXNS: • changes direction of force • provides mechanical advantage (multiplies your force)

  10. 2 TYPES: • fixed pulley- attached to something that doesn’t move used to change the direction of force doesn’t multiply force at all

  11. B. movable pulley- attached to an object being moved multiplies force

  12. BLOCK & TACKLE- when fixed & movable pulleys are used together multiplies A LOT of force used to lift car engines, etc

  13. 4. Inclined Plane • consists of a flat, sloping surface • simplest of all machines • used to move objects from 1 level to another

  14. 5. Wedge • used to push objects apart • inclined plane that moves • multiplies force and brings it to a single point

  15. 6. Screw • inclined plane wrapped around a cylinder • multiplies force • how much it increases force depends on PITCH • pitch- how far apart the threads are • smaller the pitch, the more force it multiplies

  16. Compound Machines • 2 or more simple machines put together to do work • ex: ax, scissors

  17. Mechanical Advantage • # of times a machine multiplies force • MA = resistance force effort force the greater the number, the less work you have to do all machines have a MA

  18. MA of pulley is equal to the number of rope segments pulling up the resistance force

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