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POD:

Learning Objective: Students will be able to explain how machines help to make work easier by calculating mechanical advantage to examine the relationship between the output force and input force. POD:. Machine – a device that makes doing work ___________________

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POD:

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  1. Learning Objective: Students will be able to explain how machines help to make work easier by calculating mechanical advantage to examine the relationship between the output force and input force.

  2. POD: • Machine – a device that makes doing work ___________________ • Input force: the force that you _________________ on a machine • Output force: the force that the___________________ applies

  3. POD: • Machine – a device that makes doing work __easier____ • Input force: the force that you __exert_________ on a machine • Output force: the force that the __machine________ applies

  4. Mechanical advantage: the number of times a machine increases the input force • MA = output force (in Newtons) / input force (in Newtons) • MA = Fout / Fin * Output WORK is never greater than input work, BUT output FORCE can be greater than input force

  5. Solution Steps – Ask Yourself: • What do I know? • What do I need to find out? • What procedure am I going to use? • How can I check my work? * Notice when determining mechanical advantage, there is NO UNIT.

  6. Problem 1 To open a bottle, you apply a force of 50 N to the bottle opener. The bottle opener applies a force of 775 N to the bottle cap. What is the mechanical advantage of the bottle opener?

  7. Problem 1 Answer To open a bottle, you apply a force of 50 N to the bottle opener. The bottle opener applies a force of 775 N to the bottle cap. What is the mechanical advantage of the bottle opener? • Output Force / Input Force = Mechanical Advantage • 775N / 50N = MA • MA = 15.5

  8. Problem 2 • To crack a pecan, you apply a force of 50 N to the nutcracker. The nutcracker applies a force of 150 N to the pecan. What is the mechanical advantage of the nutcracker?

  9. Problem 2 Answer • To crack a pecan, you apply a force of 50 N to the nutcracker. The nutcracker applies a force of 150 N to the pecan. What is the mechanical advantage of the nutcracker? • MA = 3

  10. Problem 3 • To pull a weed out of a garden, you can apply a force of 50 N to the shovel. The shovel applies a force of 10 N to the weed. What is the MA of the shovel?

  11. Problem 3 Answer • To pull a weed out of a garden, you can apply a force of 50 N to the shovel. The shovel applies a force of 10 N to the weed. What is the MA of the shovel? • MA = 1/5 = .2

  12. Problem 4 To pry a nail out of a wall, you can apply a force of 25 N to a hammer. The hammer applies a force of 650 N to the nail. What is the MA of the hammer?

  13. Problem 4 Answer To pry a nail out of a wall, you can apply a force of 25 N to a hammer. The hammer applies a force of 650 N to the nail. What is the MA of the hammer? MA = 26

  14. Problem 5 • The mechanical advantage of a rope is 7. To lift a block on a movable pulley, you can apply a force of 100 N to a rope. How much force does the rope apply?

  15. Problem 5 Answer • The mechanical advantage of a rope is 7. To lift a block on a movable pulley, you can apply a force of 100 N to a rope. How much force does the rope apply? Output Force = 700 N

  16. Problem 6 • You are trying to pull apart two pieces of wood using a lever. The lever applies a force of 640 N to the weed with a mechanical advantage of 32. How much force must you apply to the lever?

  17. Problem 6 Answer • You are trying to pull apart two pieces of wood using a lever. The lever applies a force of 640 N to the weed with a mechanical advantage of 32. How much force must you apply to the lever? Input Force = 20 N

  18. Problem 7 • A wedge has a mechanical advantage of 20. To lift a refrigerator, you can apply a force of 30 N to a wedge. How much force does the wedge apply?

  19. Problem 7 Answer • A wedge has a mechanical advantage of 20. To lift a refrigerator, you can apply a force of 30 N to a wedge. How much force does the wedge apply? • Output Force = 600 N

  20. Problem 8 • The output work of a machine is 35J. The input work is 70J. What is the efficiency of the machine?

  21. Problem 8 Answer • The output work of a machine is 35J. The input work is 70J. What is the efficiency of the machine? Efficiency = 50%

  22. Problem 9 The output work of a machine is 25 J. The efficiency of the machine is 100%. What is the input work?

  23. Problem 10 • What type of machine is the one from the previous question?

  24. Problem 10 Answer • What type of machine is the one from the previous question? • It is an ideal machine (100% efficient)

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