Heat & Temperature
Chapter 5
Student Learning Objectives
•Relate kinetic energy to temperature
•Compare temperature scales
•Analyze systems to determine methods
& affects of heat transfer
What does temperature measure?
Temperature is a measure
of the average kinetic
energy of the atoms and
molecules in a substance.
We perceive the KE of
atoms and molecules as
being hot or cold.
Thermal Equilibrium
 Materials at different
temperatures come to the
same temperature when
placed in contact.
Thermometer + Person
Person + Metal Chair
Thermal Expansion
 Most materials expand
when the temperature is
increased.
Metal lids
Bridge Joints
Bimetallic strips
Hot Air Balloons
Temperature
Fahrenheit & Celsius are based on boiling and
freezing points of water.
Fahrenheit Celsius
Freezing (at sea level)
Boiling (at sea level)
32o
212o
0o
100o
Kelvin is based the average KE of atoms in a gas.
F = (9/5)C + 32
C = (5/9)(F – 32)
K = C + 273
0 Kelvin = ─273o C = ─460o F
Examples
Human Body
Sun
Blue Star
Kelvin
310.15 K
5800 K
35000 K
Fahrenheit
98.6 ºF
9,980 ºF
62,540 ºF
Practice
1) Would you expect the surface temperature of
a red star to be higher or lower than the
surface temperature of our Sun?
2) What is a cold day on Earth in Fahrenheit?
What is a hot day on Earth in Fahrenheit?
Convert these temperatures to Celsius and
Kelvin.
Practice
3) Why do we rub our hands together to warm
them? What is the physics behind this
practice?
4) Do all substances expand when heated?
What is heat?
Heat is energy.
Heat flows from one
object to another if there
is a temperature
difference.
The larger the
temperature difference,
the faster heat energy
flows.
Hot → Cold
Practice
1)When ice and a warm
liquid are combined,
a. Ice cools the liquid
b. Liquid warms the ice
2) Where would be the
fastest place to cool a
very hot pizza?
a. On the counter
b. In the refrigerator
c. In the freezer
The amount of heat it takes to increase the
temperature of a material by 1o C is the specific
heat capacity of the material.
A substance with a high specific heat capacity
will resist changes in temperature.
Q = cmDT
Practice
1) Does a swimming pool lose heat quickly or
slowly during the night?
2) In a standard shower, 120 kg of hot water is
used during a 10 minute shower. What is the
heat energy required to raise the temperature
of the 120 kg of water from 15°C to 61°C?
More Practice
3) A solid copper penny is
dropped from a height of
10 meters. If all energy is
conserved within the
penny, what is the
temperature change of the
penny when it lands on
the ground?
Thinking About The World
Practice
4) Where would you expect a greater
temperature change between day and night, in
a humid location or a dry location? Why?
5) Are day to night temperature changes larger
when the sky is clear or cloudy?
What is the greenhouse effect?
The greenhouse effect traps heat near the
surface of a planet.
Greenhouse gasses slow heat loss to space.
Questions
1) What contributes most to the CO2 in our
atmosphere?
2) Is the greenhouse effect “bad”?
3) What is global warming?
What happens to temperature & energy
during a phase change?
A substance that has reached the
temperature required for a phase change
maintains its temperature during the
phase change.
DT = 0
Phase Change
All energy lost or
gained is used to change
the phase of the
substance.
Evaporation
(Liquid to gas)
Sublimation
(Solid to gas)
Condensation
(Gas to liquid)
The amount of heat energy per
kilogram that must be added or
removed for a substance to change
phase is called latent heat (L).
Q = mL
IceWaterSteam
T (°C)
100
0
Joules
Practice
1) Describe the physical processes which occur
when –20ºC ice is added to +25º soda.
2) A 50 gram piece of steel is brought into full
contact with a large block of 0o C ice, and the
system of steel and ice is isolated. If the steel
has an initial temperature of 95o C, how much
of the ice will melt?
More Practice
In lab, a 64 gram piece of hot metal (97º C) is
brought into contact with 64 grams of cold water
(23ºC), and the system is isolated. Which do you
expect to change temperature more, metal or
water? Why?
What are the three methods of heat transfer?
Conduction
Conduction is the
transfer of heat energy
from one place to
another by direct
collisions.
then
Insulators slow or
impede the rate of heat
flow.
Styrofoam
Fiberglass
Thermal conductivity of a material depends on the
movability of the electrons.
Freely moving electrons = High thermal conductivity
Pots & Pans
Metal Spoons
Convection
Convection is the transfer of heat energy
from one place to another by the bulk
motion of groups of molecules in a fluid.
Boiling Liquid
Oven
Sea Breeze
Radiation
Radiation is the
transfer of heat energy
from one place to
another by
electromagnetic waves.
(light)
Stars
Fire
People
Practice
1) Solids tend to conduct heat better than liquids
or gases. Why?
2) Does something that has a high thermal
conductivity have a high or low specific heat
capacity?
More Practice
3) Why does hot fluid rise above cool fluid?
4) Ceiling fans change direction. Why?
5) Why do people tend to wear darker colored
clothes in the winter and lighter colored
clothes in the summer?
Ideal Gas Law
In a gas, pressure is determined by temperature,
volume, and number of particles.
PV = nkT
Practice
1) A certain number of gas molecules are contained in a
tire. What happens to the tire pressure if temperature
increases?
2) A certain number of gas molecules are contained in a
balloon. What happens to the balloon pressure if
temperature decreases?
More Practice
3) When you compress air in a bicycle tire
pump, what happens?
4) On a hot day (101ºF), you measure the tire
pressure to be 38 psi. The next day, the
temperature only reaches 81 ºF. What is the
tire pressure on the cooler day?
What are the 3 laws of thermodynamics?
1st Law: The amount of heat energy transferred is
equal to the change in internal energy plus work.
Heat Energy  DIE + Work
2nd Law:
• Heat cannot flow
spontaneously from a
cold substance to a hot
substance.
Hot → Cold
• Entropy (disorder) cannot
spontaneously decrease.
3rd Law: If absolute 0 was attainable, all
particle motion would stop.
KE → 0
Entropy → 0
Practice
1) If a balloon is filled
with air, sealed, and
placed in the freezer,
will the entropy
increase, decrease, or
remain constant?
2) What would happen to
the motion, KE, and
temperature of the air
trapped in the balloon?
More Practice
Which is more
disordered?
The glass of
ice chips or
the glass of
water?