Question

Section 14.2 Work and Machines
(pages 417–420)
This section describes how machines change forces to make work easier to do. It
identifies input forces exerted on and output forces exerted by machines and
discusses input work and output work.
Reading Strategy (page 417)
Summarizing As you read, complete the table for each machine. After you
read, write a sentence summarizing the idea that your table illustrates. For
more information on this Reading Strategy, see the Reading and Study
Skills in the Skills and Reference Handbook at the end of your textbook.
Machine Increases or Decreases Increases or Decreases
Input Force Input Distance
Tire jack Decreases Increases
Lug wrench
Rowing oar
Summary: As input force decreases, the input distance increases.
Machines Do Work (pages 417–418)
1. Is the following sentence true or false? A machine can make work easier
to do by changing the size of the force needed, the direction of a force, or
the distance over which a force acts.
2. Consider the equation Work � Force � Distance. If a machine increases
the distance over which a force is exerted, the force required to do a
given amount of work .
3. You make several trips to unload a few heavy items from a car instead
of moving them all at once. Does the total distance over which you exert
yourself increase or decrease?
Work Input and Work Output (pages 419–420)
4. The work done by a machine is always less than the work done on a
machine because of . Circle the correct answer.
attraction friction gravity
Physical Science Reading and Study Workbook Level B ■ Chapter 14 163
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5. Circle the letter of the definition for input force.
a. the amount of force exerted by a machine
b. the amount of work done by a machine
c. the amount of force exerted on a machine
6. Is the following sentence true or false? Every machine uses some of its
work input to overcome friction.
7. Circle the letter of the expression that equals the work output
of a machine.
a.
b. Output distance � Input distance
c. Output distance � Output force
8. Is the following sentence true or false? Output work always is less than
input work.
For questions 9 through 11, refer to the figure below.
9. Which arrow represents the input force? Label it on the figure.
10. Which arrow represents the input distance? Label it on the figure.
11. Which arrow represents the output force? Label it on the figure.

Answer 1

Here are the completed table entries and answers to questions 1–11.

Table (finish the two rows)
- Lug wrench: Decreases (input force) — Increases (input distance)
- Rowing oar: Increases (input force) — Decreases (input distance)

Summary sentence
- As input force decreases, the input distance increases. (Machines trade force for distance or distance for force.)

Machines Do Work
1. True. A machine can change the size of a force, the direction of a force, or the distance over which a force acts.
2. Decreases. (Work = force × distance, so increasing distance allows the required force for the same work to be smaller.)
3. Increases. Making several trips means you walk the route more times, so the total distance you exert yourself over is larger.

Work Input and Work Output
4. friction.
5. c. the amount of force exerted on a machine.
6. True. Some input work is always used to overcome friction.
7. c. Output distance × Output force (Work output = Fout × dout).
8. True. Output work is always less than input work (some input is lost to friction).

Questions 9–11 (about the figure)
I don’t see the figure you mention. To label the arrows on your figure:
- Input force: label the arrow where the person (or source) applies the force to the machine (the effort/handle side).
- Input distance: label the arrow showing how far the point of application of that input force moves (the path/arc of the handle).
- Output force: label the arrow where the machine applies force to the load (the side pushing or lifting the load).

If you paste or describe the arrows/labels shown in your figure (for example “Arrows A, B, C”), I will tell you exactly which arrow to mark for each.