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

6. 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.

7. 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?

8. 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

9. 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?

10. 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

11. 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?

12. 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

13. 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?

14. 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

15. 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?

16. 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

17. 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?

18. 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

19. 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?

20. 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

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

22. 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%

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

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

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