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Understanding Machines: Principles of Work, Power, and Mechanical Advantage in Physical Science

Chapter 12 of Physical Science explores machines—devices that alter the direction or magnitude of force to aid in accomplishing work. It clarifies the roles of effort and resistance forces involved in machine operation, highlighting that machines cannot perform work independently. The chapter describes simple machines like levers, wheels and axles, pulleys, inclined planes, wedges, and screws. It explains how these machines function, their mechanical advantage, and how compound machines combine simple machines to enhance efficiency and reduce labor.

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Understanding Machines: Principles of Work, Power, and Mechanical Advantage in Physical Science

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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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