Name
CHAPTER 14
Class
Date
Heat and Temperature
SECTION
1 Temperature
KEY IDEAS
As you read this section, keep these questions in mind:
• How are temperature and energy related?
• What are the three common temperature scales?
• Why do objects feel hot or cold?
What Is Temperature?
When you touch the hood of a car, you can feel if it
is hot or cold. If someone asks you to describe the
temperature of the car, you may use those words to
describe it. However, the words hot and cold are not
very precise terms. In science, we need to describe
temperature in a more precise way.
To describe temperature precisely, you must first
know what temperature is. Temperature is closely
related to energy. Remember that matter is made up of
particles, such as atoms and molecules. These particles
are constantly moving, so they have kinetic energy.
Temperature is a measure of the average kinetic energy
of all of the particles in an object.
People take temperature readings every day. In most
cases, people use a thermometer to measure the
temperature of an object. A thermometer is a tool
that measures temperature. However, thermometers do
not directly measure the average kinetic energy of
particles. Instead, most thermometers measure the
effects of changes in the kinetic energy of particles.
READING TOOLBOX
Ask Questions As you read
this section, write down any
questions you have. When
you finish reading, try to
figure out the answers to
your questions by discussing
them with a partner.
READING CHECK
1. Identify Relationships
How is temperature related
to kinetic energy?
KXcb8Yflk@k
Discuss In a small group,
talk about why it is important
to know the temperatures of
certain things.
People use different kinds of thermometers to measure the temperatures
of different things. For example, we use a different kind of thermometer to
measure the temperature outside than to measure our body temperatures.
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How Do Thermometers Work?
READING CHECK
2. Review What happens
to temperature as kinetic
energy increases?
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3. Predict Consequences
Imagine a liquid that
contracts when its
temperature increases.
If that liquid were used
in a thermometer, what
would happen to the liquid
level when temperature
increased?
The particles in an object with a high temperature
have a great deal of kinetic energy. Remember that the
kinetic energy of an object is related to its speed. The
faster the object is moving, the higher its kinetic energy.
Therefore, the particles in a hot object are moving
quickly. However, we can’t measure the kinetic energy of
every particle in an object. How, then, can we measure
temperature?
To measure temperature using a thermometer, we
rely on the fact that most substances expand when their
temperature increases. This is because the particles are
moving faster and have more kinetic energy. Therefore,
when the particles collide, they move farther away from
one another. As the particles move apart, the substance
expands.
A common thermometer contains a hollow tube with
some liquid, such as mercury or colored alcohol, in it. On
the outside of the tube, there are markings for different
temperatures. If the kinetic energy of the particles in the
liquid increases, the liquid expands. It rises up the tube.
The liquid reaches a higher temperature marking. In this
way, we can measure the temperature of a material.
Thermometers like this one rely on liquid
expansion to measure temperature.
METAL EXPANSION IN THERMOSTATS
READING CHECK
4. Describe What does a
thermostat do?
Most metals also expand when they are heated and
contract when they are cooled. This property of
metals is used in a thermostat. A thermostat measures
and controls the temperature inside a house, building,
or machine.
A thermostat contains a coil made of strips of two
different types of metal. These two metals expand and
contract by different amounts. As the temperature falls,
the metal coil unwinds. This moves the pointer on the
thermostat to a lower temperature reading. When the
temperature rises, the coil winds up. This moves the
pointer on the thermostat in the opposite direction, to a
higher temperature reading.
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Temperature continued
The coil inside a thermostat is
made of two different metals.
The metals expand at different
rates when the temperature
changes. This causes the coil
to tighten or loosen. As the coil
moves, the pointer moves to a
different temperature reading.
EHHDBG@<EHL>K
Iron
Copper
Room temperature
5. Explain What causes
the pointer on a thermostat
to move to a different
temperature reading?
Hot
Cold
What Are the Three Temperature Scales?
If you hear someone say that it is 37 degrees outside,
would you think that it is hot or cold? Would you wear a
sweater or a T-shirt? It depends on which scale the person is using to measure temperature. There are three
different temperature scales that are commonly used.
They are the Fahrenheit, Celsius, and Kelvin scales.
People in the United States mainly use the Fahrenheit
scale to measure temperature. The units on the
Fahrenheit scale are called degrees Fahrenheit (ºF).
Water freezes at 32 ºF and boils at 212 ºF.
Most countries other than the United States use the
Celsius scale to measure temperature. Many scientists
also use this scale. The units on the Celsius scale are
called degrees Celsius (ºC). Water freezes at 0 ºC and
boils at 100 ºC.
You can convert, or change, temperature measurements in degrees Fahrenheit to measurements in degrees
Celsius. To do this, use the equations below.
Fahrenheit temperature = (1.8 Celsius temperature ) + 32.0
TF = 1.8TC + 32.0
Fahrenheit temperature – 32.0
Celsius temperature = ____________________________
1.8
T
–
32.0
F
TC = _________
1.8
READING CHECK
6. Identify What are the
three main temperature
scales?
Math Skills
7. Convert People sometimes write the “1.8” in the
equations to the left as a
fraction instead of a decimal.
What is 1.8 written as a
fraction?
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Temperature continued
ABSOLUTE ZERO AND THE KELVIN SCALE
Reading Check
8. Describe In theory,
what would happen to the
particles in a substance at
absolute zero?
Reading Check
You have probably heard people give temperatures in
negative degrees Celsius or negative degrees Fahrenheit.
This is because even below temperatures of 0 ºC or
0 ºF, particles are still moving. These particles still have
kinetic energy, so they still have a temperature. However,
in theory, there is a point at which all of the particles in a
substance stop moving. It is called absolute zero.
Based on mathematical calculations and experiments,
scientists have determined that absolute zero is equal to
2273.15 °C. The temperature of outer space is very close
to absolute zero. However, in reality, an object can never
reach exactly absolute zero. This is because the particles
in an object never completely stop moving.
Absolute zero is the basis for the Kelvin temperature
scale. Many scientists use the Kelvin scale to measure
temperature. The units for the Kelvin scale are called
kelvins (K). On this scale, absolute zero is 0 K.
Temperature measurements on the Kelvin scale do
not use the degree sign (º).
There are no negative temperature values on the Kelvin
scale. This is because absolute zero is the lowest possible
temperature. Remember that absolute zero is equal to 0 K
and 2273.15 °C. Therefore, you can convert between the
Kelvin and Celsius scales using the equation below:
9. Explain Why can’t there
be negative temperatures on
the Kelvin scale?
Kelvin temperature = Celsius temperature + 273.15
TK = TC + 273.15
Some recent scientific experiments have reached
temperatures near absolute zero. Scientists have found
that matter behaves in very unusual ways at such low
temperatures. For example, friction seems to disappear
between many surfaces near absolute zero.
The table below summarizes the main differences
between the three main temperature scales. The figure at
the top of the next page shows some common temperatures
on all three scales.
Scale
Temperature at
Temperature at
Absolute zero
which water freezes which water boils temperature
Fahrenheit 32 °F
212 °F
2459.69 °F
Celsius
0 °C
100 °C
2273.15 °C
Kelvin
273.15 K
373.15 K
0K
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Temperature continued
Common Temperatures on Three Temperature Scales
Water boils–
Summer day
in desert
Human body
temperature
Warm room
–
–
–
Cool room–
Water freezes–
–
Winter day
in plains
Winter day
in tundra–
220
210
200
190
180
170
160
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
–10
–20
–30
–40
100
370
90
360
80
350
70
340
60
330
50
320
40
310
30
300
20
290
10
280
0
270
–10
260
–20
250
–30
240
–40
230
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10. Identify What is average
human body temperature in
degrees Celsius?
11. Identify At what temperature on the Kelvin scale
does water boil?
Fahrenheit
Celsius
Kelvin
CONVERTING BETWEEN TEMPERATURE SCALES
Let’s try a problem converting between the different
temperature scales. The highest temperature recorded
on Earth was 57.8 ºC, in Libya. What is this same temperature in degrees Fahrenheit and in kelvins?
Step 1: List the given
and unknown values.
Given:
Celsius temperature,
TC = 57.8 °C
Unknown:
Fahrenheit temperature,
TF
Kelvin temperature, TK
Step 2: Write the
equations.
TF = 1.8TC + 32.0
Math Skills
12. Convert The melting
point of gold is 1,064 ˚C.
What is its melting point in
degrees Fahrenheit? Show
your work.
TK = TC + 273.16
Step 3: Insert the
known values and solve
for the unknown values.
TF = 1.8 × 57.8 °C + 32.0
TF = 136 °F
TK = 57.8 °C + 237.16
TK = 331 K
So, 57.8 ºC is the same as 136 ºF and 331 K.
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Temperature continued
How Are Temperature and Energy Transfer
Related?
READING CHECK
13. Identify When two
objects touch, in which
direction does energy move?
READING CHECK
What makes something feel hot or cold? The answer
has to do with how energy moves between objects.
When two objects at different temperatures are touching,
energy moves from one object to the other. This is
called energy transfer. Energy moves from the object
with a higher temperature to the object with a lower
temperature.
Objects feel hot or cold because of this energy
transfer. For example, imagine holding a piece of ice in
your hand. The temperature of your hand is higher than
the temperature of the ice. In other words, the molecules
in your hand are moving faster than the molecules in the
ice. Energy moves from your hand into the ice. The
molecules in the ice move faster. Their kinetic energy—
and their temperature—increases.
Where does the energy to raise the temperature of the
ice come from? Your hand. Your body loses energy when
it is transferred to the ice. The nerves in your skin sense
this loss of energy. They send a signal to your brain. Your
brain interprets the signal as a feeling of coldness. In
a similar way, energy from a high-temperature object
will move into your body. Your brain interprets this as a
feeling of heat.
14. Describe If you are
holding a hot object, does
energy flow into or out of
your hand?
Glass of
ice water
Cup of
hot tea
EHHDBG@<EHL>K
15. Illustrate On the figure,
draw arrows in each picture
to show the direction in
which heat moves.
Energy flows from objects at high temperatures to objects at lower temperatures.
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Temperature continued
HEAT
The energy that is transferred between objects at
different temperatures is called heat. Heat always moves
from an object at a higher temperature to an object at a
lower temperature. If two objects are at the same temperature, no heat will move between them. Heat moves
between two objects until their temperatures are equal.
At that point, the particles in both objects have the same
amount of kinetic energy.
8g^i^XVa I]^c`^c\
16. Apply Concepts A
student places a cup of
cold water on a counter in
a warm room. The student
measures the temperature of
the water every minute until
it stops changing. The water’s
final temperature is 28 ˚C.
What is the final temperature
of the room?
RATE OF ENERGY TRANSFER
The difference in temperature between two objects
can tell you the direction in which heat will flow. The difference in temperature between two objects can also tell
you how fast heat will flow. The greater the temperature
difference, the faster heat flows.
For example, imagine two containers of water. The
water in one container has a temperature of 60 °C. The
water in the other container has a temperature of 40 °C.
Both containers are in a room. The air in the room has a
temperature of 10 °C, as shown below.
Rate of heat transfer
from container A
Rate of heat transfer
from container B
EHHDBG@<EHL>K
Container A:
water at 60 ˚C
air: 10 ˚C
Container B:
water at 40 ˚C
17. Identify Which container
of water will lose heat the
fastest? Explain your answer.
Heat will flow from the water in the containers into
the air in the room. As heat flows, the temperature of the
water will decrease, and the temperature of the air will
increase. Heat will flow out of the warmer water faster
than out of the cooler water. As the temperature of the
water gets close to the temperature of the air, heat flows
more slowly.
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Section 1 Review
Section Vocabulary
absolute zero the temperature at which molecular energy is at a minimum (0 K on the Kelvin
scale or 2273.15 ºC on the Celsius scale)
heat the energy transferred between objects that
are at different temperatures; energy is always
transferred from higher-temperature objects
to lower-temperature objects until thermal
equilibrium is reached
temperature a measure of how hot (or cold)
something is; specifically, a measure of the
average kinetic energy of the particles in an
object
thermometer an instrument that measures and
indicates temperature
1.Compare How is temperature related to heat?
2.Calculate The thermometer in an air-conditioned room reads 20.0 ºC. What is the
temperature of the room in degrees Fahrenheit and in kelvins? Show your work.
3.Compare Which atoms are moving faster: those in a spoon at 0 ºF or those in a
fork at 0 ºC? Explain your answer. (Hint: Which is the higher temperature, 0 ºF or 0 ºC?)
4.Identify Problems A student is doing an experiment to determine the effects of
temperature on an object. He writes down that the initial temperature of the
object was –3.5 ºK. Identify two errors in the student’s recorded temperature.
5.Calculate A sample of liquid nitrogen has a temperature of –320.8 ºF. What is its
temperature in degrees Celsius and in kelvins? Show your work. (Hint: Use the
temperature in degrees Celsius to calculate the temperature in kelvins.)
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