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How Machines D o Work

How Machines D o Work. What is a machine, Mechanical advantage & efficiency. What is a machine?. Device that allows you to do work in a way that is easier change at least one of the three factors. machine. Change the amount of force you exert

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How Machines D o Work

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  1. How Machines Do Work What is a machine, Mechanical advantage & efficiency.

  2. What is a machine? • Device that allows you to do work in a way that is easier • change at least one of the three factors

  3. machine • Change the amount of force you exert • Change the distance over which you exert the force • Change the direction in which you exert the force • Machines make work easier by changing either the force, distance or direction.

  4. Input & output forces • Input force = force you exert on the machine • Output force = the force the machine exerts on an object

  5. Input and output work • Input work = input force x input distance • Output work = output force x output distance • No machine produces more work than is input.

  6. The amount of input work done by the gardener equals the amount of output work done by the shovel.

  7. Mechanical Advantage • The number of times the machine increases the force exerted on it. • MA = output force/input force

  8. Increasing force: MA > 1 • You exert an input force of 10 N • Can opener exerts an output force of 30 N • Mechanical advantage = • 30N/10N • = 3

  9. Increasing Distance: MA < 1 • You exert an Input force of 20 N on the chopsticks • Chopsticks exert an Output force of 10 N • Mechanical advantage? • 10 N/ 20 N • = 0.5 • Input distance • Output distance

  10. Changing direction • If you only change the direction, • what will be the mechanical advantage? • Mechanical advantage = 1 • Input force • Output force

  11. Efficiency • Efficiency = output work/input work x 100% • Friction reduces the efficiency of objects (like glue on scissors)

  12. Real and ideal machines • Efficiency of 100 %  ideal machine • 100 % efficiency perpetual motion machine • Unfortunately no such machine exists • All machines lose some work due to friction

  13. 1. Machine increases force, you must exert input force over a greater distanceExample: faucet

  14. 2. Machine increases distance, you must apply greater input forceExample: chopsticks

  15. 3. Machine changed direction, the amount of force and distance remain the same.Example: tricep presses

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