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Pretest
Chapter 15
1. How much work is done when a weightlifter holds a barbell
motionless over his head?
2. Calculate the work done on a 2-N mass when it is lifted to a
height of 2 m.
3. Calculate the average speed of a bicycle that travels 100 m
in 20 s.
4. Is weight a force? What is the formula for calculating weight?
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Pretest (continued)
Chapter 15
5. How does the temperature of an object change when it is acted
on by friction?
6. True or False: In a closed system, the loss of momentum of one
object equals the gain in momentum of another object.
7. How is power related to work?
8. True or False: The amount of work done on a machine (work in)
always equals the amount of work done by the machine
(work out).
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Interest Grabber
Section 15.1
How Is Energy Related to Work?
Energy is defined as the ability to do work.
Recall that work is the product of force and
distance. If a force acts through a greater
distance, it has done more work. You can
use work to measure changes in energy.
Place two identical books on a table so
there is a gap of about 8 cm between the books. Place a sheet of
notebook paper on the books so it covers the gap as shown. Now drop
a penny from a height of 10 cm onto the paper above the gap. Note
what happens. Next, drop the penny from a height of 30 cm and
observe the results.
1. How did the height of the penny affect the distance the paper
moved?
2. How did lifting the penny affect the work it did on the paper?
3. How did lifting the penny affect its energy?
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Reading Strategy
Section 15.1
Building Vocabulary
a. kinetic energy
b. the energy of motion
c. gravitational potential energy
d. elastic potential energy
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Calculating Kinetic Energy
Go to section
Section 15.1
Calculating Kinetic Energy
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Section 15.1
Calculating Kinetic Energy
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Section 15.1
Calculating Kinetic Energy
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Section 15.1
Interest Grabber
Section 15.2
How Can Energy Change Forms?
Have you even seen a Rube Goldberg device? Goldberg was an award-winning
cartoonist who drew complex series of devices that performed relatively simple
acts. The devices were arranged so that the output of one device would act as the
input of the next. Goldberg became so well known for his drawings that people all
over the world hold contests to see who can build the most complicated device.
Study the Rube Goldberg cartoon below and answer the questions.
1. List at least three kinds of energy in the device.
2. Describe one change, in which energy from one form is
converted into energy of another form.
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Reading Strategy
Section 15.2
Relating Cause and Effect
a. The gull drops the oyster, and the oyster’s gravitational potential
energy is converted into kinetic energy as the oyster falls. (Air
resistance can be ignored.)
b. The oyster strikes a rock and breaks, kinetic energy is converted
into work (breaking the shell) and thermal energy. The kinetic energy
and gravitational potential energy of the oyster are now zero.
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Conservation of
Energy
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Section 15.2
Conservation of
Energy
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Section 15.2
Conservation of
Energy
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Section 15.2
Conservation of
Energy
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Section 15.2
Interest Grabber
Section 15.3
Using Wind and Water
Wind and water are two useful sources
of energy found in nature.
You can demonstrate how these energy
sources are converted into kinetic energy
by making a model of a windmill or a water
wheel. Tape a pencil to an index card. Hold
the pencil loosely at both ends. Blow onto
one side of the index card and observe what
happens. Next, hold the index card above a bucket.
Have a classmate pour water from a pitcher onto one
side of the index card.
1. What happened when you blew into the card? What
happened when you held the card under running water?
2. How do you think people used the kinetic energy of a water
wheel or a windmill to grind corn or other kinds of grain?
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Reading Strategy
Section 15.3
Identifying Main Ideas
a. Nonrenewable energy resources include oil, natural gas and coal.
They exist in limited quantities.
b. Renewable energy resources include hydroelectric, solar, geothermal,
wind, biomass, and nuclear fusion.
c. Energy resources can be conserved by reducing energy needs and by
increasing the efficiency of energy use.
Go to section
Wind Turbine
Go to section
Section 15.3
Pretest Answers
Chapter 15
1. How much work is done when a weightlifter holds a barbell
motionless over his head?
No work is done.
2. Calculate the work done on a 2-N mass when it is lifted to a
height of 2 m.
4J
3. Calculate the average speed of a bicycle that travels 100 m
in 20 s.
5 m/s
4. Is weight a force? What is the formula for calculating weight?
Yes. W = mg.
Click the mouse button to display the answers.
Pretest Answers
Chapter 15
(continued)
5. How does the temperature of an object change when it is acted
on by friction?
the temperature increases
6. True or False: In a closed system, the loss of momentum of one
object equals the gain in momentum of another object.
7. How is power related to work?
Power is the rate at which work is done.
8. True or False: The amount of work done on a machine (work in)
always equals the amount of work done by the machine
(work out).
Click the mouse button to display the answers.
Interest Grabber
Section 15.1
Answers
1. How did the height of the penny affect the distance the
paper moved?
The paper moved farther when the penny was dropped
from a greater height.
2. How did lifting the penny affect the work it did on
the paper?
Lifting the penny allowed it to do more work on the paper.
3. How did lifting the penny affect its energy?
Lifting the penny increased the penny’s energy.
Interest Grabber
Section 15.2
Answers
1. List at least three kinds of energy in the device.
There is kinetic energy, chemical energy, and
gravitational potential energy.
2. Describe one change, in which energy from one form is
converted into energy of another form.
The chemical energy of the cannon is converted into the
kinetic energy of the peanut.
Interest Grabber
Section 15.3
Answers
1. What happened when you blew into the card? What
happened when you held the card under running water?
The moving air and water caused the card and pencil
to rotate.
2. How do you think people used the kinetic energy of a
water wheel or a windmill to grind corn or other kinds
of grain?
Answers will vary. Sample possible answer:
The kinetic energy of the windmill or water wheel
probably turned gears, which cause a millstone to turn.
Chapter 15
Go Online
Data Sharing
Self-grading assessment
Articles on energy and energy sources
For links on potential and kinetic energy, go to
www.SciLinks.org and enter the Web Code as
follows: ccn-2151.
For links on energy, go to www.SciLinks.org and enter
the Web Code as follows: ccn-2152.