1. 14.3 Mechanical Advantage and Efficiency
Key Concepts:
How does the actual mechanical advantage of a machine compare to its ideal mechanical advantage?
Why is the efficiency of a machine always less than 100%?

2. I. Mechanical Advantage
A. Number of times that a machine increases the input force.
1. Actual mechanical advantage (AMA) = Output force
Input force
2. Example: Inclined plane

3. I. Mechanical Advantage
B. Ideal Mechanical Advantage (AMA)
1. The mechanical advantage in the absence of friction.
2. Actual mechanical advantage is always less than the ideal mechanical advantage.
3. Ideal mechanical advantage = Input distance
Output distance

4. I. Mechanical Advantage
C. Practice Problems
1. A pulley is used to raise a heavy crate. The pulley is such that an input force of 223 N is needed to provide an output force of 1784 N. What is the actual mechanical advantage of this pulley?

5. I. Mechanical Advantage
2. 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 600 N to the weed. What is the actual mechanical advantage of the shovel?

6. I. Mechanical Advantage
3. Suppose you need to remove a nail from a board by using a claw hammer. If the effort length for a claw hammer is 11.0 cm and the resistance length is 2.0 cm. What is the ideal mechanical advantage?

7. I. Mechanical Advantage
4. A mover uses a ramp to load a crate of nails onto a truck. The crate, which must be lifted 1.4 m from the street to the bed of the truck, is pushed along the length of the ramp. If the ramp is m long and friction between the ramp and crate can be ignored, what is the ideal mechanical advantage of the ramp?

8. II. Efficiency
A. The work output of machine is always less than the work input due to friction.
B. To measure efficiency of a machine, compare the work output to work input.
Efficiency = Work output x 100
Work input

9. II. Efficiency C. Practice Problems
1. What is the efficiency of a cyclist who expends 900J of work to his bike for it to produce 76 J of useful work?

10. II. Efficiency
2. What is the efficiency of a tractor that has a work output of 300J and a work input of 400 J?

11. II. Efficiency
3. If a steam engine does 500 J of useful work, how much work is needed to be put in if the efficiency rating of 18%?

12. 14.4 Simple Machines Key Concepts:
1. What are the six types of simple machines?
2. What determine the mechanical advantage of the six types of simple machines?

13. 1. Levers
A. A lever is a rigid bar that is free to move around a fixed point. B. The fixed point the bar rotates around is the fulcrum. C. The input arm of a lever is the distance between the input force and the fulcrum. D. The output arm is the distance between the output force and the fulcrum.

14. 1. Levers E. 1st Class Levers
1. The fulcrum is always located between the input force and the output force.
2. Depending on the fulcrum position, the mechanical advantage can be greater than 1, equal to 1, or less than 1.

15. 1. Levers F. 2nd Class Levers
1. The output force is located between the input force and the fulcrum.
2. The input distance is larger than the output distance.
3. The mechanical advantage is always greater than 1.

16. 1. Levers G. 3rd Class Levers
1. The input force is located between the fulcrum and the output force.
2. The output distance over which it exerts the force is larger than the input distance.
3. The mechanical advantage is always less than 1.

17. 2. Wheel and Axle
A. Consists of two disks or cylinders, each one with a different radius.
B. The outer disk is the wheel and the inner cylinder is the axle.
C. To calculate the IMA, divide the radius (or diameter) where the input force is exerted by the radius (or diameter) where the output force is exerted.

18. 3. Inclined Plane
A. Slanted surface along which a force moves an object to a different elevation.
B. The distance traveled is the input distance.
C. The change in height of the ramp is its output distance.
D. The mechanical advantage is greater than 1.
E. The IMA is the distance along the inclined plane divided by its change in height.

19. 4. Wedge
A. V-shaped object whose sides are two inclined planes sloped toward each other.
B A wedge has a mechanical advantage greater than 1.

20. 5. Screw A. An inclined plane wrapped around a cylinder.
B. Screws with threads that are closer together have a greater ideal mechanical advantage.
C. A screw has a mechanical advantage greater than 1.

21. 6. Pulleys A. Consists of a rope that fits into a groove in a wheel.
B. Pulleys produce an output force that is different in size, direction, or both, from that of the input force.
C. The mechanical advantage of a pulley can be equal to or greater than 1.

22. 6. Pulleys
D. The IMA is equal to the number of rope sections supporting the load being lifted.

23. 14.4 Assignment
Page 434 #1-9 all
Read Lab: Pulleys