Section 16.1
16.1 Thermal Energy and Matter
1 FOCUS
Objectives
16.1.1 Explain how heat and work
transfer energy.
16.1.2 Relate thermal energy to the
motion of particles that make
up a material.
16.1.3 Relate temperature to thermal
energy and to thermal
expansion.
16.1.4 Calculate thermal energy,
temperature change, or mass
using the specific heat equation.
16.1.5 Describe how a calorimeter
operates and calculate thermal
energy changes or specific heat
using calorimetry
measurements.
Reading Focus
Build Vocabulary
L2
Concept Map Have students construct
a concept map of the vocabulary terms
in this section. Instruct students to place
the terms in ovals and connect the ovals
with lines on which linking words are
placed. Students should place the main
concept (Thermal Energy and Matter)
at the top. As they move away from the
main concept, the content should
become more specific.
Reading Strategy
Key Concepts
◆
What is the temperature
of an object related to?
◆
What two variables is
thermal energy related to?
◆
◆
◆
◆
heat
temperature
absolute zero
thermal expansion
specific heat
calorimeter
What causes thermal
expansion?
How is a change in
temperature related to
specific heat?
On what principle does a
calorimeter operate?
Reading Strategy
Previewing Copy the table below. Before
you read, preview the figures in this section
and add two more questions to the table. As
you read, write answers to your questions.
Questions About Thermal
Energy and Matter
Answers
Which has more thermal energy,
a cup of tea or a pitcher of juice?
a.
?
b.
?
c.
?
d.
?
e.
?
I
Figure 1 Count Rumford
supervised the drilling of brass
cannons in a factory in Bavaria.
From his observations, Rumford
concluded that heat is not a form
of matter.
n the 1700s, most scientists thought heat was a fluid called caloric
that flowed between objects. In 1798, the American-born scientist
Benjamin Thompson (1753–1814), also known as Count Rumford,
challenged this concept of heat. Rumford managed a factory that
made cannons. Figure 1 shows how a brass cylinder was drilled to
make the cannon barrel. Water was used to cool the brass so that it did
not melt. Rumford observed that the brass became hot as long as the
drilling continued, producing enough heat to boil the water. Soon after
the drilling stopped, however, the water stopped boiling. When the
drilling resumed, the water again came to a boil. Based on his observations, Rumford concluded that heat could not be a kind of matter, but
instead was related to the motion of the drill.
Work and Heat
A drill is a machine that does work on the cannon. Remember that no
machine is 100 percent efficient. Some of the work done by the drill
does useful work, but some energy is lost due to friction. Friction
causes the moving parts to heat up. The more work done by the drill,
the more that friction causes the cannon to heat up.
Heat is the transfer of thermal energy from one object to another
because of a temperature difference.
Heat flows spontaneously
from hot objects to cold objects. Heat flows from the cannon to the
water because the cannon is at a higher temperature than the water.
L2
Sample answers: a. A pitcher of juice
b. Why did Rumford conclude that heat
is not a form of matter? c. The brass was
hot enough to make water boil only
during drilling, so the heat must be
related to the motion of the drill. d. How
is specific heat related to temperature?
e. The lower a material’s specific heat,
the more its temperature rises when a
given amount of energy is absorbed by
a given mass.
Vocabulary
In what direction does
heat flow spontaneously?
474
Section Resources
2 INSTRUCT
Work and Heat
FYI
It is common usage to talk about heat
flowing. More precisely, it is thermal
energy that flows. It is always correct to
use “heat” as a verb; using “heat” as a
noun should be avoided.
474 Chapter 16
Print
• Reading and Study Workbook With
Math Support, Section 16.1 and
Math Skill: Calculating with Specific Heat
• Math Skills and Problem Solving
Workbook, Section 16.1
• Transparencies, Chapter Pretest and
Section 16.1
Technology
• Probeware Lab Manual, Lab 7
• Interactive Textbook, Section 16.1
• Presentation Pro CD-ROM, Chapter Pretest
and Section 16.1
• Go Online, NSTA SciLinks, Specific heat
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Page 475
Build Reading Literacy
Temperature
L1
Make Inferences Refer to page 472D
in this chapter, which provides the
guidelines for making inferences.
How do you know something is hot? You might use a thermometer to
measure its temperature. Temperature is a measure of how hot or cold
an object is compared to a reference point. Recall that on the Celsius
scale, the reference points are the freezing and boiling points of water.
On the Kelvin scale, another reference point is absolute zero,
which is defined as a temperature of 0 kelvins.
A
Temperature is related to the average kinetic
energy of the particles in an object due to their random
motions through space. As an object heats up, its particles
move faster, on average. As a result, the average kinetic energy
of the particles, and the temperature, must increase.
Why does heat flow from a high to a low temperature?
One way that heat flows is by the transfer of energy in collisions. On average, high-energy particles lose energy, and
low-energy particles gain energy in collisions. Overall, collisions transfer thermal energy from hot to cold objects.
Students’ understanding often depends
on how they apply prior knowledge
toward making inferences about new
situations. Have students read the two
paragraphs at the bottom of p. 474.
Invite students to describe situations
that are similar to the drill heated by
friction. Then, ask students to make an
inference: Based on what you have
read, why do your hands feel warmer
after you rub them together? (Some of
the work done is lost to friction, and so is
converted to thermal energy.)
Logical
Thermal Energy
Temperature
B
Recall that thermal energy is the total potential and kinetic
energy of all the particles in an object.
Thermal energy
depends on the mass, temperature, and phase (solid, liquid,
or gas) of an object.
Thermal energy, unlike temperature, depends on mass.
Suppose you compare a cup of tea and a teapot full of tea.
Both are at the same temperature, so the average kinetic
energy of the particles is the same in both containers.
However, there is more thermal energy in the teapot because
it contains more particles.
Now consider how thermal energy varies with temperature. You can do this by comparing a cup of hot tea with a
cup of cold tea. In both cases, the tea has the same mass,
and the same number of particles. But the average kinetic
energy of particles is higher in the hot tea, so it also has
greater thermal energy than the cold tea.
Figure 2 shows the particles in a cup of hot tea and in a
pitcher of lemonade. The tea is at a higher temperature
because its particles move a little faster, on average. But they
are only moving slightly faster, and the pitcher of lemonade
has many more particles than the tea. As it turns out, the
pitcher of lemonade has more thermal energy than the cup
of hot tea.
What is thermal energy?
L2
Students may assume from common-use
phrases such as heat transfer and heat
flow that heat is a moving substance.
Emphasize that heat is a flow, or transfer,
of thermal energy from one object or
material to another, just as work is a
transfer of mechanical energy. While
convection involves the movement of
particles of a fluid from one place to
another, there is obviously no flow of
matter when thermal energy is transferred from one solid to another. An
amount of heat, like an amount of work,
refers to how much energy is transferred.
Verbal
Figure
2 Thermal energy depends on mass and
5375
temperature.
A The tea is at a higher
& Associates
temperature than the lemonade because its
particles have a higher average kinetic energy.
B The lemonade is at a lower temperature, but
it has more thermal energy because it has many
more particles. Inferring In which liquid are
water particles moving faster, on average?
Thermal Energy and Heat
475
Customize for English Language Learners
Reading/Learning Log
Concepts such as heat, temperature, and
thermal energy are easy to misunderstand and
confuse with each other. Be sure that English
language learners have a clear understanding
of these concepts by having them construct
a Reading/Learning Log. Have students write
what they understand in the left column, and
what they still have questions about in the
right column.
Thermal Energy
Use Visuals
L1
Figure 2 Stress that the particles in
both liquids are mostly water molecules,
and that these are not simple spheres.
Ask, In what ways can a water molecule
move? (Each molecule can move to the
sides in three dimensions, rotate, and
stretch along its molecular bonds.) Point
out that some kinetic energy is present
in each of these motions, and this affects
the overall temperature of the liquid.
Visual
Answer to . . .
Figure 2 The average speed of water
particles is greater in the tea because
the average kinetic energy is greater.
Thermal energy is the
total potential and kinetic
energy of all the particles in an object.
Thermal Energy and Heat 475
Section 16.1 (continued)
Thermal Contraction and Expansion
Thermal Contraction
and Expansion
Cooling Air
Procedure
Cooling Air
L2
Objective
After completing this activity, students
will be able to
• describe the effect of temperature on
the volume of a gas.
Skills Focus Measuring, Comparing
and Contrasting
Prep Time 20 minutes
Materials round balloon, 2-L plastic
bottle, metric tape measure, plastic
bucket, ice
Advance Prep The circumference of
the balloon can be found by wrapping
a string around the balloon and then
measuring the length of the string.
Class Time 20 minutes
Safety Students should wear safety
goggles and lab aprons and must wipe
up any spills immediately to avoid falls.
Teaching Tips
• Students can calculate the volume of
the balloon from its circumference
by approximating the shape of the
balloon as a sphere and using the
equation C 2r to find the radius.
4
The volume is then given by V 3 r3.
Make sure students include the bottle
to determine the total volume of the
enclosed air.
Expected Outcome The balloon
contracts as the air in the bottle cools.
Analyze and Conclude
1. The volume decreased when cool.
2. Cooling the air inside the bottle and
balloon reduced the kinetic energy of its
particles, and therefore the pressure on
the balloon, causing it to contract.
Visual, Logical
1. Inflate a round balloon and
then stretch its opening
over the mouth of a 2-L
bottle. Use a tape measure
to measure and record the
balloon’s circumference.
2. Put a dozen ice cubes into
a plastic bucket. Add cold
water to the bucket to a
depth of 15 cm. Submerge
the bottom of the bottle in
the ice water and tape the
bottle in place.
3. After 10 minutes, measure
and record the circumference of the balloon.
Analyze and Conclude
If you take a balloon outside on a cold winter day, it shrinks. Can you
explain why? As temperature decreases, the particles that make up the
air inside the balloon move more slowly, on average. Slower particles
collide less often and exert less force, so gas pressure decreases and the
balloon contracts. This is called thermal contraction.
If you bring the balloon inside, it expands. Thermal expansion is
an increase in the volume of a material due to a temperature increase.
Thermal expansion occurs when particles of matter move farther
apart as temperature increases. Gases expand more than liquids and
liquids usually expand more than solids. A gas expands more easily
than a liquid or a solid because the forces of attraction among particles in a gas are weaker.
Thermal expansion is used in glass thermometers. As temperature
increases, the alcohol in the tube expands and its height increases. The
increase in height is proportional to the increase in temperature. In an
oven thermometer, a strip of brass and a strip of steel are bonded
together and wound up in a coil. As the coil heats up, the two metals
expand at different rates, and the coil unwinds. This causes the needle
to rotate on the temperature scale.
1. Observing How did
the volume of air in the
balloon change?
2. Inferring Explain why the
air behaved as it did.
What is thermal expansion?
Specific Heat
When a car is heated by the sun, the temperature of the metal door
increases more than the temperature of the plastic bumper. Do you
know why? One reason is that the iron in the door has a lower specific
heat than the plastic in the bumper. Specific heat is the amount of heat
needed to raise the temperature of one gram of a material by one degree
Celsius. If equal masses of iron and plastic absorb the same heat, the
iron’s temperature rises more.
The lower a material’s specific heat,
the more its temperature rises when a given amount of energy is
absorbed by a given mass.
Specific heat is often measured in joules per gram per
degree Celsius, or J/g•C. Figure 3 gives specific heats for
Specific Heats of Selected Materials
a few common materials. It takes 4.18 joules of energy to
Material (at 100 kPa)
Specific Heat (J/g•ⴗC)
raise the temperature of 1.00 gram of water by 1.00 degree
Water
4.18
Celsius. How much energy is needed to heat 2.00 grams of
Plastic (polypropylene)
1.84–2.09
water to the same temperature? You would have to add
Air
1.01
twice as much energy, or 8.36 joules.
Iron
0.449
Silver
0.235
476
Figure 3 Specific heat is the heat needed to raise the temperature of 1 gram of material by 1ºC. Analyzing Data Which
material in the table has the highest specific heat? The lowest?
Chapter 16
Facts and Figures
Specific Heat
Build Science Skills
L2
Analyzing Data Have students examine
the specific heat values in Figure 3. Ask,
Which substance requires nearly 1 J of
energy to raise the temperature of 1 g
by 1°C? (Air) What amount of energy
would be required to raise the temperature of 2.00 g of water by 1.00°C?
(4.18 2.00 8.36 J) Logical
476 Chapter 16
Thermal Contraction One of the few
exceptions to thermal expansion is water near
its freezing point. Over most temperature
ranges, water increases in volume as its
temperature increases, but between 0°C and
4°C water actually contracts as it gets warmer.
This unusual behavior occurs because hydrogen bonding between water molecules in ice
arranges them in a way that occupies a greater
volume than in liquid water. This results in
ice being less dense than liquid water. In the
winter, when a pond begins to freeze, the
denser, warmer water sinks to the bottom,
and the cooler, less dense ice floats. This forms
a layer of warmer water at the bottom of the
pond, in which fish are able to live.
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Page 477
Build Math Skills
The heat (Q) absorbed by a material equals the product of the mass
(m), the specific heat (c), and the change in temperature (ΔT).
Specific Heat
For: Links on specific heat
Visit: www.SciLinks.org
Web Code: ccn-2161
Q m c ΔT
L1
Formulas and Equations Students
should become familiar with rearrangements of the formula Q m c T,
so that any one of these quantities can
be calculated in terms of the other three.
Have students rearrange the equation
in order to calculate specific heat
c Q/(m T), mass m Q/(c ΔT),
and temperature ΔT Q/(m c).
Logical, Portfolio
In this formula, heat is in joules, mass is in grams, specific heat is in
J/g•°C, and the temperature change is in degrees Celsius.
Direct students to the Math Skills in
the Skills and Reference Handbook
at the end of the student text for
additional help.
Calculating Specific Heat
An iron skillet has a mass of 500.0 grams. The specific heat of iron
is 0.449 J/g•°C. How much heat must be absorbed to raise the
skillet’s temperature by 95.0°C?
Read and Understand
What information are you given?
1. How much heat is needed to
raise the temperature of 100.0 g
of water by 85.0°C?
Mass of iron, m 500.0 g
Specific heat of iron, c 0.449 J/g•°C
2. How much heat is absorbed by
a 750-g iron skillet when its
temperature rises from 25°C
to 125°C?
Temperature change, ΔT 95.0°C
Plan and Solve
3. In setting up an aquarium, the
heater transfers 1200 kJ of heat
to 75,000 g of water. What is
the increase in the water’s
temperature? (Hint: Rearrange
the specific heat formula to solve
for ΔT.)
What unknown are you trying to calculate?
Amount of heat needed, Q ?
What formula contains the given quantities and
the unknown?
4. To release a diamond from
its setting, a jeweler heats a
10.0-g silver ring by adding
23.5 J of heat. How much
does the temperature of the
silver increase?
Q m c ΔT
Replace each variable with its known value.
Q 500.0 g 0.449 J/g•°C 95.0°C
For Extra Help
5. What mass of water will change
its temperature by 3.0°C when
525 J of heat is added to it?
21,375 J 21.4 kJ
L2
Solutions
1. Q m c ΔT
(100.0 g)(4.18 J/g•°C)(85.0°C)
35.5 kJ
2. Q m c ΔT
(750 g)(0.449 J/g•°C)(125°C 25°C)
(750 g)(0.449 J/g•°C)(100°C) 34 kJ
3. ΔT Q/(m c)
1,200,000 J/(75,000 g 4.18 J/g•°C)
3.8°C
4. ΔT Q/(m c)
23.5 J/(10.0 g 0.235 J/g•°C)
10.0°C
5. m Q/(ΔT c)
525 J/(3.0°C 4.18 J/g•°C) 42 g
Logical
Look Back and Check
Is your answer reasonable?
Round off the data to give a quick estimate.
L1
Make sure students start by writing
out the equation required to solve each
problem. Then, check that they are able
to solve the equation for the unknown
variable using basic algebra skills.
Logical
Q 500 g 0.5 J/g•°C 100°C 25 kJ
This is close to 21.4 kJ, so the answer is reasonable.
Thermal Energy and Heat
477
Additional Problems
1. Gold has a specific heat of 0.13 J/g•°C. If a
sample of gold with a mass of 250 g undergoes
a temperature increase of 4.0°C, how much heat
does it absorb? (130 J)
2. A piece of iron at a temperature of 145.0°C cools
off to a temperature of 45.0°C. If the iron has a
mass of 10.0 g and a specific heat of 0.449 J/g•°C,
how much heat is given up? (449 J)
Logical, Portfolio
Download a worksheet on specific
heat for students to complete, and
find additional teacher support
from NSTA SciLinks.
Answer to . . .
Figure 3 Silver has the lowest
specific heat. Water has the highest
specific heat.
Thermal expansion is the
increase in volume of a
material due to a temperature increase.
Thermal Energy and Heat 477
Calorimeter
Section 16.1 (continued)
Measuring Heat Changes
Stirrer
Measuring Heat
Changes
Calorimetry
Thermometer
Lid
L2
Water
Purpose Students observe a calorimeter
measuring changes in thermal energy.
Aluminum
sample
Materials plastic foam cup with lid,
thermometer, water, iron bolt (~75 g)
Procedure Place the iron bolt in a
freezer for one hour prior to the
demonstration. Fill the cup two-thirds full
with room-temperature water and record
its temperature. Place the cold iron in the
water and cover the cup. After three
minutes, record the temperature of the
water. Ask what students can infer about
the bolt’s initial temperature.
Figure 4 A calorimeter is used to measure
specific heat. A sample to be tested is heated
and placed in the calorimeter. The lid is put on
and the temperature change is observed.
Hypothesizing Why does the calorimeter
need a stirrer?
Section 16.1 Assessment
Safety Wipe up spills immediately.
Expected Outcome Students should
conclude that the bolt was colder than
the water. Visual, Group
Reviewing Concepts
1.
2.
3 ASSESS
Evaluate
Understanding
L2
3.
Ask students to write a summary
paragraph relating thermal energy,
temperature, and heat.
Reteach
A calorimeter is an instrument used to measure changes in
thermal energy.
A calorimeter uses the principle that heat
flows from a hotter object to a colder object until both reach
the same temperature. According to the law of conservation
of energy, the thermal energy released by a test sample is equal
to the thermal energy absorbed by its surroundings. The
calorimeter is sealed to prevent thermal energy from escaping.
Figure 4 shows how a calorimeter can be used to measure
the specific heat of aluminum. A known mass of water is
added to the calorimeter. The mass of the sample of aluminum
is measured. The aluminum is heated and then placed in the
water. The calorimeter is sealed. As the aluminum cools off,
the water is stirred to distribute thermal energy evenly. The
water heats up until both the aluminum and the water are at the
same temperature. The change in temperature of the water is
measured. The thermal energy absorbed by the water is calculated using the specific heat equation. Since this same amount
of thermal energy was given off by the sample of aluminum,
the specific heat of aluminum can be calculated.
4.
5.
L1
6.
Use Figure 2 to summarize key concepts
about thermal energy.
In what direction does heat flow on its
own spontaneously?
How is the temperature of an object
related to the average kinetic energy of
its particles?
Name two variables that affect the
thermal energy of an object.
What causes thermal expansion of an
object when it is heated?
How do the temperature increases
of different materials depend on their
specific heats?
What principle explains how a calorimeter
is used to measure the specific heat of a
sample material?
Critical Thinking
7. Applying Concepts Why is it necessary to
have regularly spaced gaps between sections
of a concrete sidewalk?
Solutions
10. Q m c ΔT (1000.0 g) (0.39 J/g•°C) (45.0 25.0°C)
7800 J
11. ΔT Q/(m c)
18,200 J/(100.0 g) (4.18 J/g•°C)
43.5°C
If your class subscribes
to the Interactive Textbook, use it to
review key concepts in in Section 16.1.
Answer to . . .
Figure 4 The stirrer keeps temperature uniform.
478 Chapter 16
478
8. Predicting An iron spoon and silver spoon
have the same mass. Which becomes hotter
when both are left in hot tea for one minute?
(Hint: Use the specific heats given in Figure 3.)
9. Calculating If it takes 80.0 joules to raise the
temperature of a material by 10.0C, how
much heat must be added to cause an
additional increase of 20.0C?
10. The specific heat of copper is
0.39 J/g•°C. How much heat is needed
to raise the temperature of 1000.0 g of
copper from 25.0°C to 45.0°C?
11. A peanut burned in a calorimeter
transfers 18,200 joules to 100.0 g of
water. What is the rise in the water’s
temperature? (Hint: Rearrange the
specific heat formula to solve for T.)
Chapter 16
Section 16.1
Assessment
1. Heat flows spontaneously from hot objects
to cold objects.
2. Temperature is related to the average
kinetic energy of the particles in an object due
to their random motions through space.
3. Mass of the object, temperature
4. Particles of matter tend to move farther
apart as temperature increases.
5. The lower a material’s specific heat, the more
its temperature increases when equal amounts
of thermal energy are added to equal masses.
6. A calorimeter uses the principle that heat
flows from a hotter object to a colder object
until both reach the same temperature.
7. The gaps provide space for concrete slabs
to expand into so they do not buckle.
8. Both spoons absorb the same energy
and have the same mass. Because silver has a
lower specific heat (0.235 J/g•°C) than iron
(0.449 J/g•°C), the silver becomes hotter.
9. Doubling the temperature change doubles
the energy required, so 160 joules must
be added.
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Page 479
Section 16.2
16.2 Heat and
Thermodynamics
1 FOCUS
Objectives
Key Concepts
Why is conduction slower
in gases than in liquids
or solids?
In what natural cycles do
convection currents occur?
How does an object’s
temperature affect
radiation?
What are the three laws
of thermodynamics?
Vocabulary
◆
◆
◆
◆
◆
◆
◆
◆
◆
conduction
thermal conductor
thermal insulator
convection
convection current
radiation
thermodynamics
heat engine
waste heat
Reading Strategy
Building Vocabulary Copy the table below.
As you read, add definitions and examples to
complete the table.
Definitions
Examples
Conduction: transfer of thermal
energy without transfer of matter
Frying pan
handle heats up.
Convection: a.
?
b.
?
Radiation:
?
d.
?
c.
T
o bake cookies, you put cookie dough on a baking sheet and pop it
in the oven. When the timer goes off, you use oven mitts to pull out the
baking sheet. Why isn’t your bare arm burned by the hot air in the oven?
One reason is that air is not a very good conductor of thermal energy.
16.2.1 Describe conduction,
convection, and radiation
and identify which of these is
occurring in a given situation.
16.2.2 Classify materials as thermal
conductors or thermal
insulators.
16.2.3 Apply the law of conservation
energy to conversions between
thermal energy and other
forms of energy.
16.2.4 Apply the second law of
thermodynamics in situations
where thermal energy moves
from cooler to warmer objects.
16.2.5 State the third law of
thermodynamics.
Reading Focus
Conduction
Conduction is the transfer of thermal energy with no overall transfer
of matter. Conduction occurs within a material or between materials
that are touching. To understand conduction, look at the Newton’s
cradle in Figure 5. When a ball is pulled back and released, you might
expect all of the balls to move to the right after the impact. Instead,
most of the kinetic energy is transferred to one ball on the end. Similarly,
in conduction, collisions between particles transfer thermal energy,
without any overall transfer of matter.
Recall that forces are weak among particles in
a gas. Compared to liquids and solids, the particles
in gases are farther apart.
Conduction in gases
is slower than in liquids and solids because the
particles in a gas collide less often. In most solids,
conduction occurs as particles vibrate in place and
push on each other. In metals, conduction is faster
because some electrons are free to move about.
These free electrons collide with one another and
with atoms or ions to transfer thermal energy.
Build Vocabulary
Figure 5 Conduction is the
transfer of thermal energy
without transferring matter. This
device, called Newton’s cradle,
helps to visualize conduction.
After one ball strikes the rest,
most of the kinetic energy is
transferred to one ball on the end.
L2
Word-Part Analysis Ask students
what words they know that have the key
word parts therm, con, duct, and radia.
(Thermal energy, conductor, and radiator)
Give a definition of a word part. (Therm
means “heat,” con means “with,” duct
means “to lead,” and radia means
“rays.”) Give additional examples that
share the word parts in question.
(Thermometer, contact, deduct, radio)
Reading Strategy
L2
a. The transfer of thermal energy by the
movement of particles in a fluid b. Hot
air circulates in an oven. c. The transfer of
energy by waves moving through space
d. Heating coil of an electric stove glows.
Thermal Energy and Heat
479
2 INSTRUCT
Conduction
Use Visuals
Section Resources
Print
• Laboratory Manual, Investigations 16A
and 16B
• Reading and Study Workbook With
Math Support, Section 16.2
• Transparencies, Section 16.2
Technology
• Interactive Textbook, Section 16.2
• Presentation Pro CD-ROM, Section 16.2
• Go Online, NSTA SciLinks, Thermodynamics
L1
Figure 5 Use the Newton’s cradle to
reinforce why energy is transferred more
efficiently by conduction in a liquid or
solid. Ask, How could the balls be
arranged to demonstrate conduction
in a gas? (The balls could be detached
and spread on a table. When one ball is
rolled toward any of the others, collisions
would occur only occasionally and without
order.)
Visual
Thermal Energy and Heat 479
PPLS
Section 16.2 (continued)
Conductors and
Insulators
Thermal Conductors Figure 6 shows a frying pan on a hot
L2
Purpose To show the similarities and
differences between types of thermal
conductors and insulators.
Materials a block of wood, an
aluminum pie plate, a metal spoon,
a plastic spoon, a silk or cotton handkerchief, a metal screwdriver
Procedure Place the objects on a windowsill that is well-exposed to sunlight.
Leave half of each object lying in the
sunlight and the other half lying in the
shade. Place the screwdriver so that the
half of the metal shaft nearest the handle
is in the shade. Leave the objects in the
sunlight for at least 30 minutes. Have
each student pick up each object by the
end that has been in shade. Have them
note carefully any difference between
the temperatures of the two ends of
each object.
Safety Remind students that the parts
of the objects that have been in sunlight
may be very hot.
Expected Outcome The pie plate, the
metal spoon, and the shaft of the screwdriver are all metals, and so are good
thermal conductors. The parts of these
objects that have been in the shade
should feel warm. The wood, handkerchief, plastic spoon, and handle of the
screwdriver are thermal insulators, and
should not feel very warm.
Kinesthetic, Group
Figure 6 The arrows show how
thermal energy is conducted away
from the heat source in a metal
frying pan. Predicting Would it
be safe to touch the handle of
the wooden spoon?
stove. The bottom of the pan heats up first. The metal handle heats up
last. You can see that the flames do not directly heat the handle. The
handle heats up because the metal is a good thermal conductor.
A thermal conductor is a material that conducts thermal energy
well. A wire rack in a hot oven can burn you because the metal conducts thermal energy so quickly. Pots and pans often are made of
copper or aluminum because these are good conductors.
A thermal conductor doesn’t have to be hot. Why does a tile floor
feel colder than a wooden floor? Both floors are at room temperature.
But the tile feels colder because it is a better conductor and transfers
thermal energy rapidly away from your skin.
Thermal Insulators Why is it safe to pick up the wooden spoon
shown in Figure 6? Wood heats up slowly because it is a poor conductor of thermal energy. A material that conducts thermal energy poorly
is called a thermal insulator.
Air is a very good insulator. A double-pane window has an air space
contained between two panes of glass. The air slows down conduction
to reduce heat loss in winter and to keep heat out of a building in
summer. More expensive windows use argon gas, which is an even better
insulator than air. Wool garments and plastic foam cups are two more
examples of insulators that use trapped air to slow down conduction.
Figure 7 Convection is the
transfer of thermal energy by the
movement of particles in a fluid.
A Passing sandbags along a line is
like transferring thermal energy
by convection.
B The arrows show convection
of air in an oven.
Predicting Which part of the
oven should have the highest
temperature?
Convection
Convection is the transfer of thermal energy when particles of a fluid
move from one place to another. Look at the people building a wall
with sandbags in Figure 7A. The moving sandbags are like the particles
in a fluid. The wall grows taller as more and more sandbags arrive. In
much the same way, particles in a fluid can transfer thermal energy
from a hot area to a cold area.
B
A
Convection
Build Reading Literacy
L1
Sequence Refer to page 290D in
Chapter 10, which provides the
guidelines for a sequence.
Convection involves a sequence of steps.
Have students describe the convection
of warm air as a sequence of events,
starting with “air heated by sunlight.”
(The sequence may resemble the following:
1) The temperature of the air increases.
2) The air expands. 3) The less dense air
rises while cooler, denser air sinks.)
Logical
480 Chapter 16
Chapter 16
Customize for Inclusion Students
Learning Disabled
Learning-disabled students may process
information in different ways, depending on
their individual learning preferences and
strengths. Some may respond better to visual
stimuli, while others may learn best through
the aural or kinesthetic modes. In presenting
information for these students, involve as
many modalities as possible. For example,
teach conduction by placing a stainless steel
spoon and a plastic spoon in warm water.
Have students observe the spoons and
compare the way they feel when they are
removed from the water. In similar ways,
involve students’ aural, visual, and kinesthetic
senses to reinforce your explanation of
scientific concepts.
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Baking instructions sometimes tell you to use the top rack of an
oven. Figure 7B shows why the temperature is lower at the top of the
oven. When air at the bottom of the oven heats up, it expands and
becomes less dense than the surrounding air. Due to the difference in
density, the hot air rises. The rising air cools as it moves away from the
heat source. As a result, the coolest air is at the top of the oven.
Air circulating in an oven is an example of a convection current. A
convection current occurs when a fluid circulates in a loop as it alternately heats up and cools down. In a heated room, convection currents
help keep the temperature uniform throughout the room.
Convection currents are important in many natural cycles, such
as ocean currents, weather systems, and movements of hot rock in
Earth’s interior.
Radiation
At a picnic, you might use a charcoal grill to cook food. When you
stand to the side of the grill, heat reaches you without convection or
conduction. In much the same way, the sun warms you by radiation on
a clear day. The space between the sun and Earth has no air to transfer thermal energy. Radiation is the transfer of energy by waves
moving through space. Heat lamps used in restaurants are a familiar
example of radiation.
All objects radiate energy. As an object’s temperature
increases, the rate at which it radiates energy increases. In Figure 8,
the electric heating coil on a stove radiates so much energy that it
glows. If you are close to the heating coil, you absorb radiation, which
increases your thermal energy. In other words, it warms you up. The
farther you are from the heating coil, the less radiation you receive,
and the less it warms you.
Observing Convection
Observing
Convection
L2
Objective
Students will learn to
• use the concept of convection to
describe fluid motion.
Procedure
1. Fill a 100-mL beaker
halfway with cold water.
2. Fill a dropper pipet with
hot water colored with
food coloring. Wipe the
pipet with a paper towel so
no food coloring is on the
outside of the pipet.
3. Insert the tip of the pipet
into the cold water,
halfway between the
surface of the water and
the bottom of the beaker.
4. Slowly squeeze the pipet
bulb. Observe the water in
the beaker from the side.
Analyze and Conclude
1. Observing Describe the
motion of the colored hot
water in the beaker.
2. Inferring Explain why the
hot water behaved as it did.
3. Predicting How would
colored cold water move in
a beaker of hot water?
What is radiation?
Skills Focus Observing, Predicting
Prep Time 10 minutes
Advance Prep Provide a 500-mL
beaker of hot water with several drops
of food coloring.
Class Time 20 minutes
Safety Turn off the hot plate at the
start of the activity. Remind students not
to touch anything that is hot, to handle
glassware carefully, and to wear safety
goggles and lab aprons.
Teaching Tips
• Remind students to release the colored
water slowly, so that its movement will
depend only on its temperature.
Expected Outcome The colored water
should float to the top of the beaker.
Analyze and Conclude
1. It rose to the top of the beaker and
formed a visible layer there.
2. The warm water rose to the top due
to convection.
3. The cold water would sink.
Visual, Logical
Radiation
L2
Figure 8 A heating coil on a
stove radiates thermal energy.
The changing color of the red
arrows indicates that the farther
you are from the coil, the less
radiation you receive.
Thermal Energy and Heat
481
Facts and Figures
Blackbody Radiation Radiation itself has
no temperature because it does not consist of
matter. Matter, however, can emit and absorb
radiation. This changes the thermal energy,
and thus the temperature, of an object. A
good emitter of radiation is also a good
absorber of radiation. Because black surfaces
absorb radiation best, a perfect absorber and
emitter of radiation is called an ideal blackbody
or blackbody. Blackbodies emit radiation at
all wavelengths with a characteristic curve
that depends on the temperature of the
object. By comparing the color and brightness
of the light emitted by an unknown radiating
object to a blackbody with known properties,
the temperature of the unknown object can
be determined.
Students may confuse the term radiation
as it is used here with radiation from
nuclear decay. Explain that in both types
of radiation, energy spreads outward,
or radiates, from a source. But nuclear
decay such as alpha decay can also
transfer mass. In thermal radiation, the
mass of an object does not change
because only energy is transferred.
Verbal
Answer to . . .
Figure 6 Yes, because wood is not a
good thermal conductor.
Figure 7 Hot air rises and cools, so the
highest temperature is at the bottom of
the oven, where the heat source is.
Radiation is the transfer
of energy through space
without the help of matter to carry it.
Thermal Energy and Heat 481
Section 16.2 (continued)
Thermodynamics
Thermodynamics
Build Science Skills
L2
Applying Concepts
Purpose Students
apply the concept of
conservation of energy.
For: Links on thermodynamics
Visit: www.SciLinks.org
Web Code: ccn-2162
Materials putty (enough to make
1 golf ball-sized ball per student),
table or desktop
Class Time 10 minutes
Procedure Have students roll putty
into balls about the size of a golf ball.
Students hold the putty balls 2–3 feet
above a table or desk and then drop
them, noting the changes that occur.
The study of conversions between thermal energy and other forms of
energy is called thermodynamics. Count Rumford made a good start
in this field. But many scientists still believed that heat was a kind of
matter. Then in 1845, James Prescott Joule (1818–1889) published his
results from a convincing experiment.
Joule carefully measured the energy changes in a system. Recall
that a system is any group of objects that interact with one another.
Joule’s system included a falling weight that turned a paddle wheel in
a container of water. As the weight fell, the paddle churned a known
mass of water. The water heated up due to friction from the turning
paddle. Joule carefully measured the work done by the falling weight.
He found that the work almost exactly equaled the thermal energy
gained by the water. Joule is often given credit for discovering the
first law of thermodynamics. That is the law of conservation of
energy applied to work, heat, and thermal energy.
First Law of Thermodynamics Recall that
energy cannot be created or destroyed. But energy can be converted into different forms.
The first law of
thermodynamics states that energy is conserved. If
energy is added to a system, it can either increase the thermal energy of the system or do work on the system. But no
matter what happens, all of the energy added to the system
can be accounted for. Energy is conserved.
Look at the bicycle pump in Figure 9. You can consider
the tire, the pump, and the air inside to be a system. The
force exerted on the pump does work on the system. Some
of this work is useful; it compresses air into the tire. The
rest of the work is converted into thermal energy. That is
why a bicycle pump heats up as you inflate a tire.
Expected Outcome The potential
energy of the putty ball held above the
table will be converted to kinetic energy
when the ball is released. Finally, it will
stick to the table, and so undergo a
decrease in kinetic and potential energy.
According to the first law of thermodynamics, none of the energy is lost. Some
of the mechanical energy is applied to
changing the shape of the putty ball. The
rest is converted to increasing the thermal
energy of both the putty and the table,
though increased thermal energy may not
be detectable due to the small amount of
energy involved. Logical
L2
Students may assume that adding
energy to a system by heating it will
only increase the system’s thermal
energy. Explain that work may be done,
or internal energy may increase (during
a phase change). Sometimes the added
heat is mostly used to increase the
thermal energy of the system, and little
work is done. Demonstrate this effect by
placing a sealed bottle of apple juice on
a sunny windowsill. Only a small amount
of work will be done because of the rigid
walls of the bottle, but the temperature
of the juice will increase. Work is negligible compared to the amount of energy
added to the juice. Kinesthetic
Download a worksheet on
thermodynamics for students to
complete, and find additional
teacher support from NSTA SciLinks.
482 Chapter 16
Figure 9 You can consider the bicycle pump, the
tire, and the air inside of both to be a system. The
person does work on the system by pushing on
the pump. Some of the work is converted into
thermal energy, which heats the air in the pump
and the tire.
482
Second Law of Thermodynamics If you take a
cold drink from the refrigerator and leave it out in a warm
room, will the drink become colder? Of course it won’t.
You know that the drink will warm up. Thermal energy
flows spontaneously only from hotter to colder objects.
The second law of thermodynamics states that
thermal energy can flow from colder objects to hotter
objects only if work is done on the system. A refrigerator, for example, must do work to transfer thermal energy
from the cold food compartment to the warm room air.
The thermal energy is released by coils at the bottom or in
the back of the refrigerator.
Chapter 16
Facts and Figures
The “Zeroth” Law of Thermodynamics
In order for a thermometer to give meaningful
information, its temperature must be equal
to that of the object whose temperature is
unknown. This occurs when both objects are
in a state of thermal equilibrium, or when the
thermal energy transferred by heat from the
object to the thermometer is equal to the heat
from the thermometer to the object. This is the
same as saying that there is no net heat transfer
between the object and thermometer.
The definition of thermal equilibrium is
the basis of what is called the “zeroth” law
of thermodynamics—two systems in thermal
equilibrium with a third system are in thermal
equilibrium with each other. As the name
implies, this concept is fundamental to
thermodynamics, and the first three laws are
dependent on it. The zeroth law was established after the first two laws of thermodynamics
had been accepted.
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Integrate Space Science
A heat engine is any device that converts heat into work. One consequence of the second law of thermodynamics is that the efficiency of
a heat engine is always less than 100 percent. The best an engine can do
is to convert most of the input energy into useful work. Thermal energy
that is not converted into work is called waste heat. Waste heat is lost to
the surrounding environment. In fact, a heat engine can do work only if
some waste heat flows to a colder environment outside the engine.
Spontaneous changes will always make a system less orderly, unless
work is done on the system. For example, if you walk long enough,
your shoelaces will become untied. But the opposite won’t happen;
shoelaces don’t tie themselves. Disorder in the universe as a whole is
always increasing. You can only increase order on a local level. For
instance, you can stop and tie your shoelaces. But this requires work.
Because work always produces waste heat, you contribute to the disorder of the universe when you stop to tie a shoelace!
Third Law of Thermodynamics The efficiency of a heat
engine increases with a greater difference between the high temperature inside and the cold temperature outside the engine. In theory, a
heat engine could be 100 percent efficient if the cold outside environment were at absolute zero (0 kelvins). But this would violate the
third law of thermodynamics.
The third law of thermodynamics
states that absolute zero cannot be reached. Scientists have been able
to cool matter almost all of the way to absolute zero. Figure 10 shows
the equipment used to produce the record lowest temperature, just
3 billionths of a kelvin above absolute zero!
Figure 10 The third law of
thermodynamics states that
absolute zero cannot be reached.
This physicist is adjusting a laser
used to cool rubidium atoms to
3 billionths of a kelvin above
absolute zero. This record low
temperature was produced
by a team of scientists at the
National Institute of Standards
and Technology.
3 ASSESS
Evaluate
Understanding
Section 16.2 Assessment
Reviewing Concepts
1.
2.
3.
4.
5.
6.
7.
8.
Why is conduction in gases slower than
conduction in liquids or solids?
Give three examples of convection
currents that occur in natural cycles.
What happens to radiation from an object
as its temperature increases?
State the first law of thermodynamics.
In your own words, what is the second
law of thermodynamics?
State the third law of thermodynamics.
Why does a metal spoon feel colder than a
wooden spoon at room temperature?
Why is solar energy transferred to Earth by
radiation?
Critical Thinking
9. Applying Concepts If your bedroom is cold,
you might feel warmer with several thin
blankets than with one thick one. Explain why.
10. Relating Cause and Effect If every
object is radiating constantly, why aren’t
all objects getting colder?
Conservation of Energy Review energy
conservation in Section 15.2. Describe how
the first and the second laws of thermodynamics are consistent with the law of conservation of energy.
Thermal Energy and Heat
Section 16.2
Assessment
1. Because particles in a gas collide less often
than in a liquid or solid
2. Ocean currents, weather systems, the
movement of molten rock in Earth’s interior
3. Its rate of radiation increases.
4. The first law of thermodynamics states that
energy is conserved.
5. Heat can flow from a colder place to a warmer
place only if work is done on the system.
6. Absolute zero cannot be reached.
L2
As the universe has expanded, its overall
temperature has decreased. Evidence of
this is provided by background radiation
that astronomers detect in the universe.
This radiation is left over from the big
bang, in which the universe was formed
13.7 billion years ago. The radiation
fills the universe uniformly, and so has
expanded with the universe. As a result,
the radiation has undergone a Doppler
shift toward low-energy radio waves
called microwaves. These microwaves
correspond to the radiation emitted by a
blackbody with a temperature of 2.7 K, or
just below three degrees above absolute
zero. Were the universe to expand indefinitely, the background radiation would
continue to decrease in energy, but it
would always be greater than zero, so the
temperature of the universe must always
be above absolute zero.
Logical
483
7. The metal feels colder because it is a better
thermal conductor, and it transfers energy more
rapidly from the warm hand to the cool room.
8. Radiation is the only type of energy transfer
that can occur through a vacuum.
9. The thin blankets trap air between the
layers, and air is a good insulator.
10. Objects both radiate and absorb thermal
energy. If an object is cooler than its
surroundings, it absorbs more energy than it
radiates, and so it heats up.
L2
Ask students to list three examples each
of conduction, convection, and radiation.
In each example, have them explain how
thermal energy is transferred for that
example and how energy is conserved
in each case.
Reteach
L1
Use Figures 5 through 8 to review heat
transfer, emphasizing how thermal
energy is changed in each case.
Energy is conserved in both laws. In the
first law of thermodynamics, thermal
energy added to a system either increases
the thermal energy of the system or is
used to do work. In the second law of
thermodynamics, when work is done
to transfer thermal energy from a cold
object to a hot object, some of the work
is converted into thermal energy.
If your class subscribes to
the Interactive Textbook, use it to
review key concepts in Section 16.2.
Thermal Energy and Heat 483
Solar Home
Solar Home
L2
Background
Huge amounts of radiant energy from
the sun constantly fall on the surface of
our planet. How can this energy be
harnessed to help make a home that is
warm and comfortable in all seasons?
Solar heating for the home can consist
of either “passive” systems, which do
not use any mechanical device to
distribute the fluids heated by the sun,
or “active” systems that use fans or
pumps to transfer the heated fluids.
Although it is not practical to use solar
heating systems to completely meet
heating needs year round, solar heating
systems can reduce the amount of
energy used in conventional heating
systems, thus reducing heating costs.
Build Science Skills
Observing
Purpose Students
observe how passive solar
heating can be used for heating.
Materials a box with black interior,
a box with white interior, clear plastic
wrap, 2 beakers, 2 thermometers
Class Time 50 minutes preparation,
or one class period
Positioning for sunlight
Windows should face south to trap as
much light as possible from the winter
sun, with few windows on the west
side to reduce overheating in summer.
Procedure Separate students into
groups, each with its own set of materials.
Members of each group place one beaker,
half full of water, in each of their boxes
and cover both boxes with plastic wrap.
Both boxes are placed in sunlight for half
an hour. Group members then remove
the beakers from the boxes, placing a
thermometer in each. Finally, all students
record the temperature of the water.
Trees on south
and west sides for
summer shade
Evergreens provide a
year-round windbreak.
Deciduous trees
give summer shade.
N
Summer sun
W
E
N
S
W
Safety Have students wear lab aprons
and safety goggles.
484 Chapter 16
Automated louvers for
cooling when needed
Heating a home with solar energy means making
the best use of available sunlight. To provide
warmth, large windows are placed on the south
side of the house to trap sunlight, while northfacing walls have good insulation and few
windows. On the roof, solar collectors absorb
energy from the sun’s rays to heat water, while
solar panels convert the sun’s energy to electrical
energy for use in household appliances. Highquality insulation is used in all outside walls to
reduce heat lost through convection, conduction,
and radiation. But because the sun does not shine
continuously, solar-heated homes also use energy
from conventional sources to keep the home
heated day and night, year-round.
L2
Expected Outcome Because the black
box absorbs and remits radiation better
than the white box, the thermal energy
of its walls and interior will be greater.
The water will be in thermal equilibrium
with the interior of the box. Therefore,
the water that had been in the black box
will have a higher temperature than the
water in the white box.
Kinesthetic, Group
Large area of glass to trap
radiant energy from the sun
E
Winter
S
sun
484
Chapter 16
Planting trees and shrubs
Trees placed away from the house act as a windbreak to reduce heat loss. Deciduous trees,
planted closer, prevent overheating in summer,
and allow sunlight to pass through in winter.
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Going Further
Student posters should clearly show
energy sources and energy transfers in
solar-heated and conventionally heated
pools. Diagrams should label places
where radiation, absorption, and
convection occur. For example,
absorption occurs in the solar collector
and convection occurs in the tubing
that carries heated water to the pool. To
reduce heat loss in a solar-heated pool,
insulating plastic is placed on the water’s
surface when the pool is not in use.
Visual
Solar panel to
generate electricity
Solar collector
to heat water
Well-insulated
timber-framed
walls
Small windows to
reduce heat loss
Sun’s rays
Solar panels
Solar panels use the sun’s energy
to generate electricity for the
home. The panels are made up of
a series of linked photovoltaic
cells. Light from the sun releases
electrons from silicon atoms in
the cells, producing an electric
current. Rechargeable batteries
can store electrical energy to
provide power when there is no
sunlight.
Entertainment or
communication
appliance
Rechargeable
battery
Solar panel
on roof
Air
conditioning
system
Lighting
Electric circuit
Cooking appliance
Heating system
Stud frame
Plasterboard
Insulating
material
Wall insulation
Wood is a natural
insulator, so timber
construction reduces heat
flow through the walls.
Filling the wall cavity
with insulating material
seals the walls against
drafts, and greatly
reduces heat loss.
Wood siding
Going Further
Research solar-heated pools in the library or on
the Internet. Make a poster display explaining
how solar heating differs from
a typical pool heating system.
Include diagrams that explain
how radiation, absorption,
insulation, and convection are
used in a solar-heated pool.
Take a Discovery Channel
Video Field Trip by watching
“Powered by the Sun.”
Video Field Trip
Thermal Energy and Heat
Video Field Trip
Powered by the Sun
After students have viewed the Video Field Trip,
ask them the following questions: How long is
energy from the sun expected to be available?
(Billions of years) Why is it important to make
effective use of solar energy? (Other sources of
energy are being constantly used up.) How does
the building at the Rocky Mountain Institute
manage to produce crops throughout the year?
(By using a greenhouse with glass walls that let in
485
sunlight. Student answers may include that a
greenhouse also stays warm inside partly by keeping
out the colder air outside.) How does the heating
system in the Rocky Mountain Institute building
produce heat? (It converts sunlight into thermal
energy.) How does this heating system work?
(Solar panels absorb sunlight and heat a fluid. The
fluid is pumped to a very large water tank. Heat from
the stored hot fluid is transferred to the water that
people use. Students may comment that the water
can be heated to between 130°C and 140°C even in
the coldest weather.)
Thermal Energy and Heat 485
Section 16.3
16.3 Using Heat
1 FOCUS
Objectives
16.3.1 Describe heat engines and
explain how heat engines
convert thermal energy into
mechanical energy.
16.3.2 Describe how the different
types of heating systems
operate.
16.3.3 Describe how cooling systems,
such as refrigerators and air
conditioners, operate.
16.3.4 Evaluate benefits and drawbacks of different heating and
cooling systems.
Key Concepts
Vocabulary
What are the two main
types of heat engines?
◆
How do most heating
systems distribute thermal
energy?
◆
◆
How does a heat pump
reverse the normal flow
of heat?
◆
◆
Intake stroke:
Fuel and air
enter cylinder.
Power
stroke: b. ?
L2
Heat Engines
Figure 11 In an external
combustion engine, combustion
occurs outside of the engine.
Heat engines played a key role in the development of the modern
industrial world.
The two main types of heat engines are the
external combustion engine and the internal combustion engine.
Hot steam in
Slide valve
Exhaust
steam out
Valve
rod
2 INSTRUCT
Piston rod
Heat Engines
Cylinder
Piston
External Combustion Engine A steam engine is an
external combustion engine—an engine that burns fuel outside
the engine. Thomas Newcomen developed the first practical steam
engine in 1712. His engine was used to pump water out of coal
mines. In 1765, James Watt designed an engine that was more efficient, in part because it operated at a higher temperature.
Figure 11 shows one type of steam engine. Hot steam enters
the cylinder on the right side. When the valve slides to the left,
hot steam is trapped in the cylinder. The steam expands and
cools as it pushes the piston to the left. Thus heat is converted
into work. The piston moves back and forth as hot steam enters
first on one side and then on the other side.
L1
Relate Cause and Effect Refer to
page 260D in Chapter 9, which
provides the guidelines for relating
cause and effect.
Have students read the paragraphs about
the external combustion engine and
study the illustration in Figure 11. Ask,
What causes the piston in the cylinder
to do work? (The expanding steam
pushes the piston, causing it to do work.)
What is the effect of the movement of
the slide valve? (It traps hot steam in the
cylinder and allows cool steam to leave.)
Logical
486 Chapter 16
Compression
stroke: a. ?
team locomotives were one of the most important early uses of the
steam engine. Prior to the locomotive, steam engines provided power
for coal mines and mills. But don’t think that steam engines are only a
thing of the past. In fact, most electric power plants today use steam
turbines, a very efficient kind of steam engine.
L2
a. Piston compresses the fuel-air mixture.
b. Ignited mixture expands and pushes
the piston. c. Exhaust gases leave the
cylinder.
Build Reading Literacy
Sequencing Copy the cycle diagram below
and complete it as you read to show the
sequence of events in a gasoline engine.
S
LINCS Have students: List the parts of
the vocabulary that they know, such as
central, heating, system, heat, and pump.
Imagine what a central heating system
might look like and how the terms
might fit together. Note a reminding,
sound-alike term, such as central nervous
system or sound system. Connect the
terms, perhaps in a long sentence or a
short story. Self-test (quiz themselves).
Reading Strategy
Reading Strategy
Exhaust
stroke: c. ?
Reading Focus
Build Vocabulary
external
combustion engine
internal combustion
engine
central heating
system
heat pump
refrigerant
486
Chapter 16
Section Resources
Print
• Reading and Study Workbook With
Math Support, Section 16.3
• Math Skills and Problem Solving
Workbook, Section 16.3
• Transparencies, Section 16.3
Technology
• Interactive Textbook, Section 16.3
• Presentation Pro CD-ROM, Section 16.3
• Go Online, Science News, Heat
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Use Community
Resources
Internal Combustion Engine Most cars use internal combustion engines that burn gasoline. An internal combustion engine is
a heat engine in which the fuel burns inside the engine. Most internal
combustion engines use pistons that move up and down inside cylinders. Each upward or downward motion of a piston is called a stroke.
The linear motion of each stroke is converted into rotary motion by the
crankshaft. The crankshaft is connected to the transmission, which is
linked to the vehicle’s wheels through the drive shaft.
Figure 12 shows the sequence of events in one cylinder of a fourstroke engine. In the intake stroke, a mixture of air and gasoline vapor
enters the cylinder. Next, in the compression stroke, the piston compresses the gas mixture. At the end of compression, the spark plug
ignites the mixture, which heats the gas under pressure. In the power
stroke, the hot gas expands and drives the piston down. During the
exhaust stroke, gas leaves the cylinder, and the cycle repeats.
Recall that a heat engine must discharge some waste energy in order
to do work. In an internal combustion engine, the cooling system and
exhaust transfer heat from the engine to the environment. A coolant—
usually water and antifreeze—absorbs some thermal energy from the
engine and then passes through the radiator. A fan blows air through the
radiator, transferring thermal energy to the atmosphere. Without a
cooling system, an engine would be damaged by thermal expansion. If
you are ever in a car that overheats, stop driving and allow the engine
to cool. Otherwise, there is a risk of serious damage to the engine.
Gasoline engines are more efficient than old-fashioned steam
engines, but they still are not very efficient. Only about one third of the
fuel energy in a gasoline engine is converted to work. Auto makers have
tried several ways to make engines more efficient. One design, called a
hybrid design, uses a heat engine together with an electric motor. This
design is explained in the How It Works box on the next page.
For: Activity on four-stroke engines
Visit: PHSchool.com
Web Code: ccp-2163
Build Science Skills
Figure 12 In an internal
combustion engine, fuel is burned
inside the engine. Most cars have
a four-stroke internal combustion
engine. This diagram shows only
one of the cylinders during each
stroke. Classifying In which of
the strokes does the piston do
work that can be used by the car?
Spark
plug
Intake
valve
L2
Applying Concepts Have students
write a short paragraph about how the
increased temperature of the gasolineair mixture allows it to do work during
the power stroke in an internal
combustion engine. Remind them to
use what they know about forms of
energy and the relationship between
temperature, pressure, and average
kinetic energy of particles that make up
a substance. (Answers should indicate
that the energy released during ignition of
the gasoline-air mixture increases the
mixture’s temperature, and thus the
average kinetic energy of the gas particles.
This greater energy produces an increase
in gas pressure, which in turn does work.)
Verbal, Logical
Exhaust
valve
Air-fuel
mixture
Cylinder
L2
Suggest that students learn more about
internal combustion engines by visiting
an auto repair shop and talking with a
mechanic. Encourage students to
construct a KWL chart, and to ask the
mechanic questions based on what
students want to learn about engines.
Interpersonal, Portfolio
Exhaust
gases
For: Activity on four-stroke engines
Visit: PHSchool.com
Web Code: ccp-2163
Piston
Students can interact with a
simulation of a four-stroke engine
online.
A
Intake stroke
B
Compression stroke
C
Power stroke
D
Exhaust stroke
Thermal Energy and Heat
487
Customize for English Language Learners
Simplify the Presentation
The details in the operations of heat engines,
heat systems, and cooling systems are rather
complex. By simplifying your presentation, the
English language learners in your class will have
a better comprehension of the material. Speak
directly, use simple words and short sentences,
and make frequent use of the diagrams to
clarify the workings of thermal systems.
Answer to . . .
Figure 12 Work is done during the
power stroke as the expanding gases
push the piston out of the cylinder.
Thermal Energy and Heat 487
IPLS
Section 16.3 (continued)
Hybrid Automobile
Hybrid Automobile
L2
The hybrid automobile is a result of
research that was begun initially to
develop an efficient electric car. By
combining a small gasoline engine with
an electric motor, the hybrid automobile
is able to travel longer distances, like a
gasoline-powered vehicle, but with
reduced fuel consumption and emissions.
During regenerative braking, kinetic
energy that is normally lost to friction is
partially recovered for later use. This can
be explained to students in simple terms:
It takes work to turn a generator. When
the spinning wheels do the work of
turning the generator, the wheels lose
kinetic energy. In other words, the wheels
must slow down.
Internal combustion engines produce harmful
emissions from the combustion of gasoline. Recently,
cleaner electric cars have been developed, but these need
frequent recharging. Hybrid cars solve these problems by
using a combination of smaller gasoline engines and electric
motors. Interpreting Diagrams Which features of the
hybrid automobile help to reduce fuel consumption?
Lightweight materials A small
engine and synthetic materials, such
as carbon fiber, reduce the car’s
weight to improve fuel efficiency.
L3
Interested students can make a
multimedia presentation for the class
explaining the hybrid automobile.
Numerous articles on the subject can
be found on the Internet and in science
and engineering periodicals.
Verbal, Portfolio
Transmission This converts
the rotation of shafts in the
electric motor and the gas
engine into wheel rotation. In
this model, both the electric
motor and the engine can
directly drive the transmission.
488
488 Chapter 16
Battery The battery
stores energy for the
electric motor.
Gasoline engine This
small heat engine is most
efficient for cruising at
constant speed. It is
assisted by the electric
motor during acceleration.
Interpreting Diagrams Fuel
consumption is reduced by using
lightweight materials, an aerodynamic
design, and high-pressure tires that
reduce friction. The use of two engines
saves fuel because the small gasoline
engine is more efficient than traditional
larger engines, and the electric motor is
more efficient than a gasoline engine for
accelerating at low speeds.
Visual
For Enrichment
Aerodynamic body
The teardrop shape
reduces air resistance,
improving efficiency.
A new breed of car
This hybrid car was first
produced in 1999. It is light,
aerodynamic, and has a
small, efficient engine.
Chapter 16
Fuel
tank
Electric motor The electric
motor is more efficient
than a heat engine for
accelerating at low speeds.
When the brakes are used,
the electric motor acts as a
generator, recharging the
batteries. This way of generating power is called
regenerative braking.
Tires These tires are
inflated to a higher
pressure than conventional
tires to reduce friction.
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Heating Systems
Heating Systems
At the start of the industrial revolution, wood-burning fireplaces were
the principal method of heating buildings. Rumford was keenly aware
of the drawbacks of fireplaces. They were smoky and not very efficient.
Too much heat went up the chimney. In 1796, Rumford designed a fireplace that now bears his name. His fireplace was not as deep as standard
fireplaces, and it had slanted walls to reflect heat into the room. His
improvements were quickly accepted and used throughout England.
Today, fireplaces are often used to supplement central heating systems. A central heating system heats many rooms from one central
location. The central location of a heating system often is in the
basement. The most commonly used energy sources for central heating systems are electrical energy, natural gas, oil, and coal. Heating
systems differ in how they transfer thermal energy to the rest of the
building.
Most heating systems use convection to distribute
thermal energy.
Hot-Water Heating Figure 13 shows the main components of
a hot-water heating system. At the boiler, heating oil or natural gas
burns and heats the water. The circulating pump carries the hot water
to radiators in each room. The hot water transfers thermal energy to
the radiator by conduction. As the pipes heat up, they
heat the room air by conduction and radiation. Hot air
rises and sets up a convection current in each room.
After transferring much of its thermal energy to the
room, the cooled water returns to the boiler and the
cycle begins again.
Radiator
Temperature is controlled by a thermostat. One
kind of thermostat is like a thermometer, with a strip of
brass and steel wound up in a coil. When the heating
system is on, the coil heats up. The two metals in the
coil expand at different rates, and the coil rotates. This
trips a switch to turn off the heat. As the room cools,
the coil rotates in the opposite direction, until it trips
the switch to turn the heat back on.
L2
Figure 13 Within the pipes of
this hot-water heating system, the
water circulates in a convection
current. In each room, the air
moves in a convection current.
Relating Cause and Effect Why
has the water returning to the
boiler cooled down?
Thermostat
Exhaust
vent
Use Visuals
Expansion
tank
Steam Heating Steam heating is very similar to
hot-water heating except that steam is used instead of
hot water. The transfer of heat from the steam-heated
radiator to the room still occurs by conduction and
radiation. Steam heating often is used in older buildings or when many buildings are heated from one
central location.
How are fireplaces often
used today?
Students may think that heating systems
are simply energy conversion devices
because they can use a variety of energy
sources to produce thermal energy.
Remind students that the energy required
to operate a heating system exceeds the
amount of thermal energy distributed by
the system, partly because there is always
some energy that is lost through exhaust
in the original central heating process.
In addition, energy is lost through heat
transfer processes from pipes and ducts
that transfer heated fluids from the central
heating system to the various rooms. Even
in electric heating, some energy is lost in
heating the wires used to transfer electrical energy to the heating coils.
Logical
Boiler
L1
Figure 13 Point out that the system
shown must be well insulated so as to
prevent the loss of heat. Have students
look at the various parts of the hot-water
heating system. Ask, Where can
thermal energy be lost in this system,
and by what manner of heat transfer?
(Energy is lost through the water pipes
leading from the boiler to the radiator.
Most of this energy is lost by radiation,
though some conduction to the air takes
place. A good deal of energy is lost by
convection from the exhaust vent. A
smaller amount of heat is lost through the
pipes leading from radiators to the boiler.)
Visual
Circulating
pump
Thermal Energy and Heat
489
Facts and Figures
Heat of Vaporization Although hot-water
heating and steam heating systems are similar
in structure, steam systems convey more
energy for each kilogram of water used. This
difference occurs because the phase change
that takes place during the boiling process,
when liquid water is vaporized to steam,
requires a much greater input of energy than is
necessary to heat water in a hot-water system.
The energy required for this phase change,
called the heat of vaporization, is equal to
2.26 106 J/kg. This amount is more than
500 times as great as the energy required to
raise the temperature of a kilogram of liquid
water by 1°C (about 4180 J/kg). When steam
completely condenses to liquid water, an
amount of energy equal to the heat of
vaporization is given up. This is why steam
heating is effective, and also why steam is
so hazardous.
Answer to . . .
Figure 13 Water returning to the
boiler has cooled because it has lost
thermal energy in the radiator.
Today, fireplaces are
often used to supplement central heating systems.
Thermal Energy and Heat 489
Section 16.3 (continued)
Cooling Systems
Cool air
sinks
Cooling by Evaporation
Hot air
rises
L2
Supply
vent
Purpose Students observe how
evaporation of a liquid can cool its
surroundings.
Materials paper towels, water, tape,
hand-held or electric fan, thermometer
Procedure Wrap a wet paper towel
around the bulb of a thermometer and
wait several minutes. Record the thermometer’s temperature. Tape the wet
paper towel to the thermometer’s bulb.
Blow air across the paper towel with the
fan. Read the thermometer’s temperature again.
Duct
Furnace
Safety Clean up any spills immediately.
Handle thermometers with care to avoid
breakage. Be sure cords are untangled
and cannot trip anyone. Do not handle
electrical equipment with wet hands.
Figure 14 In a forced-air central heating
system, the hot air enters the room through
a supply vent in the floor. The hot air rises as
cooler, denser air in the room sinks. The
cooler air returns to the furnace through the
return vent. Inferring If the hot air supply
vent were located near the ceiling, what
would be the warmest part of the room?
Expected Outcome Water absorbs
energy as it evaporates. This removes
energy from the thermometer bulb,
so the temperature reading of the
thermometer decreases.
Kinesthetic, Visual
Integrate Chemistry
490 Chapter 16
Forced-Air Heating To maintain even
room temperatures, forced-air heating systems
use fans to circulate warm air through ducts to
the rooms of a building. In a forced-air heating
system, shown in Figure 15, convection circulates
air in each room. Because the warm air entering
the room rises toward the ceiling, the warm-air
vents are located near the floor. Cool room air
returns to the furnace through floor vents on the
other side of the room. One advantage of forcedair heating is that the air is cleaned as it passes
through filters located near the furnace.
How do forced-air heating
systems circulate air?
Cooling Systems
L2
Different compounds can be used as
refrigerants, just as long as they can be
made to evaporate at low temperatures.
Among the refrigerants that have this
property are certain chlorofluorocarbons,
or CFCs, which have been used widely
in refrigerators and air conditioners. In
the 1970s, chlorine atoms released by
CFCs were found to react with the layer
of atmospheric ozone, which absorbs
harmful ultraviolet radiation from the
sun. The decomposition of the ozone
layer prompted the establishment of the
Montreal Accords in 1990 and the
eventual replacement of CFCs with less
harmful refrigerants.
Verbal, Logical
Science News provides students
with current information on heat.
Chimney
Return
vent
Electric Baseboard Heating An electric
baseboard heater uses electrical energy to heat a
room. A conductor similar to the heating element
in an electric stove is used to convert electrical
energy to thermal energy. The hot coil heats the
air near it by conduction and radiation. Then convection circulates the warm air to heat the room.
Radiant heaters are similar to electric baseboard heating. They are often sold as small
portable units, and are used to supplement a
central heating system. These “space heaters” are
easy to turn on and off and to direct onto cold
toes or other areas where heat is needed most.
Sometimes these heaters have a fan that helps to
circulate heat.
For: Articles on heat
Visit: PHSchool.com
Web Code: cce-2163
490
Chapter 16
Most cooling systems, such as refrigerators and air conditioners, are
heat pumps. A heat pump is a device that reverses the normal flow of
thermal energy. Heat pumps do this by circulating a refrigerant
through tubing. A refrigerant is a fluid that vaporizes and condenses
inside the tubing of a heat pump. When the refrigerant absorbs heat,
it vaporizes, or turns into a gas. When the refrigerant gives off heat, it
condenses, or turns back into a liquid.
Recall that thermal energy flows spontaneously from hot objects to
cold objects.
Heat pumps must do work on a refrigerant in order
to reverse the normal flow of thermal energy. In this process, a cold
area, such as the inside of a refrigerator, becomes even colder.
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Comparing Washing Machines
$70
Cost per Year
What Is the Real Cost of a
Washing Machine?
If you ever shop for a new washing machine, you’ll
notice the bright yellow Energy Guide sticker on
each machine. The sticker gives the machine’s
operating cost per year as estimated by the U.S.
Department of Energy. The largest part of the cost
for cleaning clothes is heating the water that goes
into the washing machine. So a machine that uses
less water is more efficient.
1. Using Graphs One family uses an electric
water heater. What is their cost per year for
machine A? For machine D?
2. Calculating How much money does this
family save each year using machine A
compared to using machine D?
3. Calculating The price of machine A is $300
more than the price of machine D. If the
family uses a machine for 10 years, which
$60
Electric water heater
$50
Gas water heater
What Is the Real Cost
of a Washing Machine?
$40
$30
$20
$10
Brand A Brand B Brand C Brand D
Washing Machines
one costs less overall? (Hint: Add the price to
the operating cost for 10 years.)
4. Calculating Another family uses a gas water
heater. Which machine should this family
choose? Explain your thinking.
5. Evaluating and Revising A washing machine
advertisement states that the annual cost
assumes an electric water heater is used. Why
would an advertisement include only this cost?
Refrigerators A refrigerator is a heat pump—
it transfers thermal energy from the cold food
compartment to the warm room. To move heat
from a colder to a warmer location, a motor must
do work to move refrigerant through tubing inside
the refrigerator walls. Could you cool your kitchen
on a hot day by leaving the refrigerator door open?
It might seem so, but an open refrigerator would
actually heat the kitchen! You may have noticed the
hot coils underneath or behind the refrigerator. The
coils not only release heat absorbed from the food
compartment; they also release thermal energy produced by the work the motor does. That is why a
refrigerator with an open door adds more heat to
the room than it removes.
What is a heat pump?
For Extra Help
L1
Discuss the basic features of a bar graph.
Unlike line graphs, in which one quantity
on the horizontal axis corresponds to a
unique quantity on the vertical axis, more
than one bar can be given for a particular
item on the horizontal axis. For instance,
in the above graph, each brand has two
bars shown: one for electric heaters and
one for gas heaters. Similarly, a comparison between results in different years can
be shown using several bars. The placement of the bars allows easy comparison
of changes on one graph. Visual
Temperature in
room: 25ⴗC
Temperature
inside
refrigerator: 3ⴗC
Figure 15 When a refrigerator door is open, some
thermal energy from the room enters the refrigerator.
But more thermal energy leaves the refrigerator through
the coils underneath the food compartment.
Interpreting Photos Why can’t you cool a room by
leaving the refrigerator door open?
Thermal Energy and Heat
L2
Answers
1. The annual cost of Brand A is about
$10 per year. The annual cost of Brand D
is $60 per year.
2. The family saves $50 each year using
Brand A.
3. The operating cost of Brand A for
10 years is 10 $10 $100. The
operating cost of Brand D for 10 years
is 10 $60 $600. Brand A costs less
overall because although the initial price
is $300 higher, the machine saves $500
in operating costs.
4. Using a gas water heater, Brand A saves
only $20 in operating costs each year.
Based only on cost, the family should
choose Brand D because it will cost $100
less to own and operate for 10 years.
5. The goal of the advertisement is to
convince as many people as possible
to buy the machine. Therefore, the
advertisement emphasizes the money
that could be saved under the best
of circumstances (using an electric
water heater).
491
Answer to . . .
Figure 14 The ceiling, because warm
air entering the room tends to remain
near the ceiling
Facts and Figures
Water Cooling Although refrigerants are used
to reach temperatures below the freezing point
of water, water itself has been used for cooling
for centuries. Because of its specific heat and
heat of vaporization, water can greatly reduce
the temperature of hot dry air. Fountains helped
to cool the air in courtyards in places like Spain
and Italy. In many desert cities, evaporative
coolers, in which hot air is drawn through watersoaked pads into houses, are still widely used for
air conditioning.
Figure 15 The refrigerator gives off
more thermal energy than it absorbs.
In a forced-air heating
system, fans circulate
warm air through ducts to the rooms
of a building.
A heat pump is a device
that reverses the normal
flow of thermal energy.
Thermal Energy and Heat 491
Section 16.3 (continued)
Use Visuals
Warm
air out
L1
Figure 16 Stress that evaporation is
the key process for cooling in an air
conditioner and refrigerator. Most of the
work done by the air conditioner motor
involves changing the pressure of the
refrigerant so that it will evaporate (and so
absorb thermal energy) and condense (to
give up thermal energy) easily. Ask, What
is the direction of the net flow of
thermal energy in an air conditioner?
(Looking at the red arrows only, thermal
energy is transferred from the air inside the
room to the outdoor air.)
Visual
3 ASSESS
Evaluate
Understanding
L2
Ask students to write two questions each
about heating systems and cooling
systems. Review the questions for
accuracy, and then have students
form groups and ask each other their
approved questions.
Reteach
L1
Use Figure 12 to review how an internal
combustion engine operates during
one cycle.
Air Conditioners Have you ever been
outside on a hot day and stood near a room air
conditioner? The air conditioner is actually
Cold
heating the outdoor air. Near the air conditioner
air out
is the last place you’d want to be on a hot day!
Where does the hot air come from? It must
come from inside the house. But as you know
from the second law of thermodynamics, heat
only flows from a lower temperature (indoors)
to a higher temperature (outdoors) if work is
done on the system.
Figure 16 shows how a room air conditioner
Warm
operates. The compressor raises the temperaair in
ture and pressure of the refrigerant, turning it
Evaporator coil
Liquid absorbs heat
into a hot, high-pressure gas. The temperature
to become vapor.
of the condenser coil is higher than the outside
air temperature, so heat flows spontaneously from the coil to the outside air. A fan increases the rate at which heat flows. As thermal energy
is removed from the coil, the refrigerant cools and condenses into
a liquid.
The liquid refrigerant then flows through the expansion valve and
decreases in temperature. As the cold refrigerant flows through the
evaporator coil, it absorbs thermal energy from the warm room air.
The fan sends cold air back into the room. The refrigerant becomes a
vapor, and the process starts all over again.
Condenser coil
Vapor cools to liquid
as heat is removed.
Compressor
Expansion valve
Pressure drops, causing liquid
refrigerant to become cold.
Figure 16 In a window air
conditioner, outside air is heated
as a fan blows it through the
condenser coil. Inside the room, a
fan draws in warm air through the
evaporator coil. The fan blows
cooled air out into the room.
Interpreting Diagrams What
work is done by the compressor?
Section 16.3 Assessment
Reviewing Concepts
1.
2.
Student flyers should clearly compare
four heating systems. Students may
choose to show the comparisons using a
chart. Possible columns in the chart are
efficiency, physical space used per room,
environmental concerns, and local
climate. Students may choose to
compare systems in different climates. In
southern states, a benefit of a forced-air
heating system is that it combines easily
with central air conditioning. Electric
baseboard heating is advantageous
in regions where electric power is
inexpensive.
If your class subscribes to
the Interactive Textbook, use it to
review key concepts in Section 16.3.
Answer to . . .
Figure 16 The compressor does work
by pushing particles of vapor closer
together to form a high-pressure vapor.
It also does work as it pushes refrigerant through the tubing.
492 Chapter 16
List the two main types of heat engines.
How is thermal energy distributed in most
heating systems?
3.
How does a heat pump move thermal
energy from a cold area to a warm area?
4. If the efficiency of a gasoline engine is
25 percent, what happens to the missing 75
percent of the energy in the fuel?
Critical Thinking
5. Predicting A diesel engine runs at a higher
temperature than a gasoline engine. Predict
which engine would be more efficient. Explain
your answer.
492
6. Applying Concepts Why would it be a
mistake to locate a wood-burning stove on
the second floor of a two-story house?
Writing to Persuade Imagine that you are
a marketing executive in a company that sells
HVAC (heating, ventilation, and air conditioning) equipment. Write a one-page flyer comparing four kinds of heating systems. Organize
the flyer so it is easy for customers to see the
benefits of each system.
Chapter 16
Section 16.3
Assessment
1. External combustion engine, internal
combustion engine
2. Most heating systems distribute thermal
energy by convection.
3. Heat pumps must do work on a refrigerant
in order to reverse the normal flow of heat.
4. The energy that does not do useful work is
converted into thermal energy.
5. The maximum efficiency of a heat engine
increases with a greater difference between
the temperature inside and the temperature
outside the engine. A diesel engine is likely
to be more efficient, assuming both engines
discharge thermal energy into an environment
at the same temperature.
6. Convection will carry cool air to the lower
level so the lower level will be cooler than the
upper level. This is inefficient because if the
lower level is comfortable, the upper level will
be warmer than necessary.
PHYSICS
Chapter 16
CHAPTER
ASSESS PRIOR
KNOWLEDGE
Thermal Energy
and Heat
Use the Chapter Pretest below to assess
students’ prior knowledge. As needed,
review these Science Concepts and
Math Skills with students.
Review Science Concepts
Section 16.1 Review work, kinetic
energy, and thermal energy. Remind
students of the Celsius and Kelvin
temperature scales used in science.
Review how matter consists of atoms,
ions, and molecules.
Section 16.2 Review efficiency of
machines and the law of conservation of
energy. Remind students of the definition
of absolute zero.
Section 16.3 Review the states of
matter. Review chemical energy and
energy conversions.
How do science concepts apply to your
world? Here are some questions you’ll be
able to answer after you read this chapter.
■
When a car has been warmed by the sun, why
is the metal door hotter than the plastic
bumper? (Section 16.1)
■
Why doesn’t hot air burn your unprotected
arm when you reach into an oven?
(Section 16.2)
■
Why does a bicycle pump heat up when you
pump up a tire? (Section 16.2)
■
What energy-saving strategies are used in a
solar-heated home? (page 484)
■
Why must a car engine have a cooling system?
(Section 16.3)
■
Can you cool a kitchen by leaving the
refrigerator door open? (Section 16.3)
Review Math Skills
Scientific Notation, Calculating
with Significant Figures, Formulas
and Equations Students will need to
manipulate 4-variable formulas to
calculate specific heat.
Direct students to the Math Skills in the
Skills and Reference Handbook at the
end of the student text.
As this locomotive steams along, it uses 䉴
thermal energy to do the work of
climbing a hill.
472
Chapter 16
Chapter Pretest
1. True or False: Degrees Celsius and kelvins
are units of temperature. (True)
2. What kind of energy is released when
bonds between atoms are broken?
(Chemical energy)
3. True or False: Thermal energy is the total
potential and kinetic energy of the microscopic particles in an object. (True)
4. The change of state from liquid to gas is
called
. (vaporization)
472 Chapter 16
5. Which of the following is the energy of
a moving object? (d)
a. Mechanical energy
b. Chemical energy
c. Potential energy
d. Kinetic energy
6. The principle that energy cannot be
created or destroyed is known as the law of
.
(conservation of energy)
7. Define work. (Work is a transfer
of energy.)
8. If the input work for a simple
machine is 21.0 J, and the output work
is 7.0 J, the efficiency of the machine is
. (c)
a. 3.0%
b. 0.33%
c. 33%
d. 30%
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PHYSICS
Chapter Preview
ENGAGE/EXPLORE
16.1
Thermal Energy and
Matter
16.2
Heat and
Thermodynamics
Video Field Trip
16.3
Using Heat
Powered by the Sun
What Happens When
Hot and Cold
Liquids Mix?
L2
Purpose Students recognize that the
final temperature of a mixture depends
on the masses and temperatures of the
substances that are mixed.
Students may think that because the
temperature of the cold water added is
the same for both mixtures, the final
temperature should be similar. To help
remedy this misconception, ask what
else may affect the final temperature.
Skills Focus Observing, Inferring,
Measuring
Prep Time 15 minutes
Materials 2 plastic foam cups, glass
stirring rod, thermometer, 2 100-mL
graduated cylinders
Class Time 20 minutes
What Happens When Hot and Cold Liquids Mix?
Procedure
Think About It
1. Fill one graduated cylinder with hot water
and another with cold water. CAUTION Be
careful when handling hot liquids. Use a
thermometer to measure the temperature of
the water in each graduated cylinder. Record
the temperatures.
1. Comparing and Contrasting How did the
final temperatures in Steps 2 and 3 compare?
2. Pour 100 mL of hot water into a plastic foam
cup. Add 100 mL of cold water to the cup.
Stir the water with a glass rod, and measure
and record its temperature.
3. Controlling Variables Why do you think it
was important to use the same graduated
cylinders in Step 3 that you used in Step 2?
2. Relating Cause and Effect What factors
can you identify that determine the final
temperature when you mix hot water with
cold water?
3. Repeat Step 2, this time adding 50 mL of cold
water to 100 mL of hot water.
Thermal Energy and Heat
Video Field Trip
Powered by the Sun
Encourage students to view the Video Field Trip
“Powered by the Sun.”
473
Safety Students should use tongs
or wear heat-resistant gloves when
handling hot glassware. Use nonmercury thermometers.
Teaching Tips
• Hot and cold tap water should be
sufficient to show the desired results.
Water could be cooled in a freezer to
increase the temperature difference.
• Students should stir the mixtures
before measuring the temperature.
• Students should do the first trial
rapidly so that the water temperatures
are the same for both trials.
Expected Outcome The cup that
received 100 mL of cold water will
be cooler.
Think About It
1. The mixture to which 50 mL of
cold water was added had a higher
temperature.
2. Students may cite the temperatures
and “amounts” of water added. They
may also say that energy or heat changed
the temperature of the water.
3. Using the same source of hot and cold
water ensures that the temperatures used
will be close to the same in both trials.
Logical, Group
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Using Specific Heat
to Analyze Metals
Using Specific Heat
to Analyze Metals
L2
Objective
After completing this lab, students will
be able to
• describe how specific heat is
determined.
In this lab, you will determine the specific heat of
steel and aluminum. Then you will use specific heat
to analyze the composition of a metal can.
Problem
How can you use specific heat to
determine the composition of a metal can?
Materials
• 10 steel bolts
• balance
• 50-cm length
of string
• clamp
• ring stand
• boiling water bath
(shared with class)
5. Use the clamp to move the bolts into the cup
of ice water. Cover the cup and insert the
thermometer through the hole in the cover.
• thermometer
• 500-mL graduated
cylinder
• ice water
• foam cup with lid
• aluminum nails
• crushed can
6. Gently swirl the water in the cup. Record the
highest temperature as the final temperature
for both the water and the steel bolts.
7. Calculate and record the specific heat of steel.
(Hint: Use the equation Q m c T to
calculate the energy the water absorbs.)
For the probeware version of this lab, see
the Probeware Lab Manual, Lab 7.
Skills
8. Repeat Steps 3 through 7 with aluminum nails
to determine the specific heat of aluminum.
Start by making a new data table. Use a mass
of aluminum that is close to the mass you used
for the steel bolts.
Calculating, Designing Experiments
Procedure
Part A: Determining Specific Heat
Part B: Design Your Own Experiment
9. Designing Experiments Design an
experiment that uses specific heat to identify
the metals a can might be made of.
1. Copy the data table shown below.
Data Table
Water
Mass (g)
Initial temperature (ⴗC)
Final temperature (ⴗC)
Specific heat (J/g•ⴗC)
Steel Bolt
4.18
10. Construct a data table in which to record your
observations. After your teacher approves your
plan, perform your experiment.
Analyze and Conclude
1. Comparing and Contrasting Which metal
has a higher specific heat, aluminum or steel?
2. Measure and record the mass of 10 steel bolts.
3. Tie the bolts to the string. Use a clamp and
ring stand to suspend the bolts in the boiling
water bath. CAUTION Be careful not to splash
boiling water. After a few minutes, record the
water temperature as the initial temperature of
the bolts.
4. Use a graduated cylinder to pour 200 mL of
ice water (without ice) into the foam cup.
Record the mass and temperature of the ice
water. (Hint: The density of water is 1 g/mL.)
2. Drawing Conclusions Was the specific heat
of the can closer to the specific heat of steel or
of aluminum? What can you conclude about
the material in the can?
3. Evaluating Did your observations prove
what the can was made of? If not, what other
information would you need to be sure?
4. Inferring The can you used is often called a
tin can. The specific heat of tin is 0.23 J/g•C.
Did your data support the idea that the can
was made mostly of tin? Explain your answer.
Thermal Energy and Heat 493
Expected Outcome Students should measure a
specific heat for the steel can that is close to that of
the steel bolts.
Sample Data Ten bolts with a mass of 100 g will
raise the temperature of 200 mL of water by about
5°C. The same mass of aluminum nails will raise
the temperature by about 9°C.
Analyze and Conclude
1. The specific heat of aluminum (about
0.90 J/g•°C) is higher than the specific heat of
steel (about 0.45 J/g•°C).
2. The specific heat of the can was very close to
the specific heat of steel. This is evidence that the
can is made mostly of steel.
3. The observations support the idea that the can
is made of steel, but do not prove it; other metals
may have similar specific heats. A list of the specific
heats of various metals for comparison would be
helpful, as would other kinds of evidence, such as
the densities and chemical properties of the metals.
4. The specific heat of the can is close to that of
steel, suggesting that the can is primarily steel.
Logical
Students may have the misconception
that the temperatures of the metal and
water are the only factors that will affect
the final temperature of the mixture. To
help dispel this misconception, ask them
to compare the effects of dropping an ice
cube into a lake and into a glass of water.
Skills Focus Calculating,
Measuring, Designing Experiments
Prep Time 20 minutes
Advance Prep Crush a steel can for
each lab group. Smooth any rough or
sharp edges with a file while wearing
heavy leather gloves and safety goggles.
Puncture the lids of the foam cups to
enable students to insert the thermometers. Provide a large beaker of boiling
water (with a thermometer in it) on a hot
plate for the entire class to use. Provide
ring stands, clamps, and 50-cm lengths
of string for suspending the bolts in the
boiling water bath.
Class Time 45 minutes
Safety Provide only nonmercury thermometers. Students should use tongs
or heat-resistant gloves when handling
hot objects and liquids. Students should
wear safety goggles and lab aprons and
should not stir with the thermometers.
Teaching Tips
• Students may need some guidance in
using the specific-heat equation.
Questioning Strategies Ask students
the following questions. Why is it important to quickly transfer the bolts into
the beaker? (Because the bolts are very
hot, they will lose thermal energy very
quickly as soon as they leave the hot
water.) Why is it important to swirl
the water after adding the hot bolts?
(This ensures an even temperature and
more accurate results.)
Probeware Lab Manual
Versions of this lab for use
with probeware available from
Pasco, Texas Instruments, and
Vernier are in the Probeware
Lab Manual.
Thermal Energy and Heat 493