Temperature, Heat, and the
First Law of Thermodynamics
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18-1 TEMPERATURE
After reading this module, you should be able to . . .
18.01 Identify the lowest temperature as 0 on the Kelvin scale
(absolute zero).
18.02 Explain the zeroth law of thermodynamics.
18.03 Explain the conditions for the triple-point temperature.
18.04 Explain the conditions for measuring a temperature
with a constant-volume gas thermometer.
18.05 For a constant-volume gas thermometer, relate the
pressure and temperature of the gas in some given state
to the pressure and temperature at the triple point.
● Temperature is an SI base quantity related to our sense of
hot and cold. It is measured with a thermometer, which contains a working substance with a measurable property, such
as length or pressure, that changes in a regular way as the
substance becomes hotter or colder.
● When a thermometer and some other object are placed in
contact with each other, they eventually reach thermal equilibrium. The reading of the thermometer is then taken to be the
temperature of the other object. The process provides consistent and useful temperature measurements because of the
zeroth law of thermodynamics: If bodies A and B are each in
thermal equilibrium with a third body C (the thermometer),
then A and B are in thermal equilibrium with each other.
● In the SI system, temperature is measured on the Kelvin
scale, which is based on the triple point of water (273.16 K).
Other temperatures are then defined by use of a constantvolume gas thermometer, in which a sample of gas is maintained at constant volume so its pressure is proportional to its
temperature. We define the temperature T as measured with
a gas thermometer to be
Here T is in kelvins, and p 3 and p are the pressures of
the gas at 273.16 K and the measured temperature,
respectively.
T ϭ (273.16 K) lim
gas:0
p
p 3
.
Learning Objectives
Key Ideas
What Is Physics?
One of the principal branches of physics and engineering is thermodynamics,
which is the study and application of the thermal energy (often called the
internal energy) of systems. One of the central concepts of thermodynamics is
temperature. Since childhood, you have been developing a working knowledge
of thermal energy and temperature. For example, you know to be cautious with
hot foods and hot stoves and to store perishable foods in cool or cold compartments. You also know how to control the temperature inside home and car, and
how to protect yourself from wind chill and heat stroke.
Examples of how thermodynamics figures into everyday engineering and
science are countless. Automobile engineers are concerned with the heating of a
car engine, such as during a NASCAR race. Food engineers are concerned both
with the proper heating of foods, such as pizzas being microwaved, and with the
proper cooling of foods, such as TV dinners being quickly frozen at a processing
plant. Geologists are concerned with the transfer of thermal energy in an El Niño
event and in the gradual warming of ice expanses in the Arctic and Antarctic.
First Law of Thermodynamics
C
H
A
P
T
E
R
1
8
514
18-1 TEMPERATURE
After reading this module, you should be able to . . .
18.01 Identify the lowest temperature as 0 on the Kelvin scale
(absolute zero).
18.02 Explain the zeroth law of thermodynamics.
18.03 Explain the conditions for the triple-point temperature.
18.04 Explain the conditions for measuring a temperature
with a constant-volume gas thermometer.
18.05 For a constant-volume gas thermometer, relate the
pressure and temperature of the gas in some given state
to the pressure and temperature at the triple point.
● Temperature is an SI base quantity related to our sense of
hot and cold. It is measured with a thermometer, which contains a working substance with a measurable property, such
as length or pressure, that changes in a regular way as the
substance becomes hotter or colder.
● When a thermometer and some other object are placed in
contact with each other, they eventually reach thermal equilibrium. The reading of the thermometer is then taken to be the
temperature of the other object. The process provides consistent and useful temperature measurements because of the
zeroth law of thermodynamics: If bodies A and B are each in
thermal equilibrium with a third body C (the thermometer),
then A and B are in thermal equilibrium with each other.
● In the SI system, temperature is measured on the Kelvin
scale, which is based on the triple point of water (273.16 K).
Other temperatures are then defined by use of a constantvolume gas thermometer, in which a sample of gas is maintained at constant volume so its pressure is proportional to its
temperature. We define the temperature T as measured with
a gas thermometer to be
Here T is in kelvins, and p 3 and p are the pressures of
the gas at 273.16 K and the measured temperature,
respectively.
T ϭ (273.16 K) lim
gas:0
p
p 3
.
Learning Objectives
Key Ideas
What Is Physics?
One of the principal branches of physics and engineering is thermodynamics,
which is the study and application of the thermal energy (often called the
internal energy) of systems. One of the central concepts of thermodynamics is
temperature. Since childhood, you have been developing a working knowledge
of thermal energy and temperature. For example, you know to be cautious with
hot foods and hot stoves and to store perishable foods in cool or cold compartments. You also know how to control the temperature inside home and car, and
how to protect yourself from wind chill and heat stroke.
Examples of how thermodynamics figures into everyday engineering and
science are countless. Automobile engineers are concerned with the heating of a
car engine, such as during a NASCAR race. Food engineers are concerned both
with the proper heating of foods, such as pizzas being microwaved, and with the
proper cooling of foods, such as TV dinners being quickly frozen at a processing
plant. Geologists are concerned with the transfer of thermal energy in an El Niño
event and in the gradual warming of ice expanses in the Arctic and Antarctic.