Chapter 15 – Section 1
Temperature and Thermal Energy
Pages 434 - 437
What is Temperature?
• Temperature is a measure of the average
value of the kinetic energy of the molecules
in random motion.
• Molecules have more kinetic energy when
they are moving faster.
faster
What is Temperature?
• The higher the temperature,
temperature the faster the
molecules are moving.
Thermal Expansion
• Almost all substances expand when they
are heated and contract when they are
cooled.
cooled
• The amount of expansion & contraction
depends on the type of material and
change in temperature.
temperature
• For example, liquids usually expand more
than solids.
Example of Thermal Expansion
Measuring Temperature
• Thermometers are used to
measure the expansion and
contraction of materials to
measure temperature.
• When the temperature of a
liquid increases,
increases it expands
so the height of the liquid in
the tube increases.
Temperature Scales
•
Three different
temperature scales that
are used to measure
temperature are degrees:
1)
Fahrenheit (°F)
2)
Celsius (°C)
3)
Kelvin (°K)
Temperature
Notable Temperatures
Absolute Zero
Celsius = Fahrenheit
Freezing Point of Water
Human Body Temperature
Boiling Point of Water
o
F
-460
-40
32
98.6
212
Temperature
o
C
-273
-40
0
37
100
Temperature
o
K
0
233
273
310
373
Converting Temperature Scales
• Fahrenheit to Celsius: °C = (°F – 32) ÷ 1.8
• Celsius to Fahrenheit: °F = (1.8 * °C) + 32
• Celsius to Kelvin = °C + 273
• Kelvin to Celsius = °K - 273
Practice Problem #1
• On a hot summer day, a Fahrenheit
thermometer shows the temperature to be
86°F. What is the temperature on the
Celsius scale?
•
•
•
Formula: Temp (°C) = (°F – 32) ÷ 1.8
Substitute: Temp (°C) = (86 – 32) ÷ 1.8
Solve: Temp (°C) = 54 ÷ 1.8 = 30° C
Practice Problem #2
• A temperature of 57°C was recorded in
1913 at Death Valley in California. What is
this temperature on the Fahrenheit scale?
•
•
•
Formula: Temp (°F) = (1.8 * °C) + 32
Substitute: Temp (°F) = (1.8 * 57) + 32
Solve: Temp (°F) = 102.6 + 32 = 134.6° F
Practice Problem Table
• Use the temperature conversion formulas
to complete the table below:
Temperature
o
F
Temperature
o
C
Temperature
o
K
0
-18
255
32
0
273
55
13
286
100
37
310
150
65
338
175
79
352
212
100
373
Thermal Energy
• So, the temperature of an object is related
to the average kinetic energy of the
molecules.
• Molecules also have potential energy,
which can be converted to kinetic energy.
• The sum of the kinetic and potential energy
of all the molecules in an object is the
thermal energy.
energy