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Mechanical Advantage

Mechanical Advantage . & Efficiency. advantage of machines. machines help us do tasks; they give us an advantage example : a lever can be used to lift a load if the load is 36N and we only apply 12N of force to lift it, then we can figure out the advantage of the lever

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Mechanical Advantage

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  1. Mechanical Advantage & Efficiency

  2. advantage of machines • machines help us do tasks; they give us an advantage • example: a lever can be used to lift a load • if the load is 36N and we only apply 12N of force to lift it, then we can figure out the advantage of the lever • ie: (36N/12N = 3 X greater)

  3. mechanical advantage • there are 2 ways to look at this advantage: • actual mechanical advantage (AMA) • ratio of load force to effort force (FL/FE) • ideal mechanical advantage (IMA) • ratio of effort arm to load arm (dE/dL) • most machines involve friction, so AMA<IMA

  4. typical IMAs

  5. practice • In an acrobatic demonstration, one person jumps onto the end of a plank (lever). This creates a large effort force of 920 N at the end of the board at a distance of 1.7 m from the fulcrum. A smaller person (460 N) located 3.1 m from the fulcrum, is launched into the air. Calculate: (a) the AMA of the board (b) the IMA of the board

  6. NOTICE • since AMA and IMA are calculated ratios they have no units!!! • (units cancel out)

  7. static and moving components • when a machine is in static equilibrium, the law of the lever applies, so: dE/dL = FL/FE and the IMA equals the AMA • when the components of the machine move, the effort force increases to account for friction, so: dE/dL > FL/FE and the IMA is greater than the AMA

  8. force advantage (AMA) • can be greater than 1, equal to 1, or less than 1

  9. efficiency • the efficiency of a machine tells us how productive it is • percent efficiency is the ratio of actual mechanical advantage to ideal mechanical advantage as a percentage % efficiency = AMA x 100 IMA

  10. practice • Calculate the percent efficiency in each of the following: (a) the distance ratio of a lever is 3.6 and the force ratio is 3.1 (b) the AMA of a wheel and axle is 6.0 and the IMA is 7.0

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