Chapter 9
Thermal Energy
Presented by April Senger
Thermal Energy
• Thermal Energy in a substance
is the total energy of all it
atoms and molecules
• It consists of both PE & KE of
the particles in the substance
• All particles are vibrating
Presented by April Senger
Temperature
• To distinguish how
warm or cold an object
is we use temperature
• The most common
temp is measured in
Celsius (0 freezing, 37
body temp & 100
boiling)
• Fahrenheit is common
in the US (32 freezing,
98.6 body, & 212
boiling)
• Kelvin is the SI unit for
measuring temp
• Degrees C and F are
not the same size
• How does a
thermometer work?
• What does that have to
do with KE?
Presented by April Senger
Concept Check
• True or False…
• Temperature is a measure of
the total kinetic energy in a
substance
• False…it is the average
temperature of the substance
Presented by April Senger
Absolute Zero
• The lower limit of temperature is called
absolute zero
• This is the temp that theoretically all
motion and vibrations would stop = no KE
• -273 degrees Celsius is A. Zero
• 0 K is also A. Zero
• To convert C to K – Add 273 to the
temperature in Celsius
• This is because C and K have the same
size of degree markings
• Caution: we do not use the work degree
with the Kelvin scale
Presented by April Senger
Hot Stuff!
• Heat is the thermal energy
transferred from one substance to
another due to a temperature
difference between the substances
• Substance contain thermal energy
NOT heat
• Heat is thermal energy that is
moving to another object
• Thermal energy flows from higher
temps to lower temps
Presented by April Senger
Cool It..
• If you step out of the pool on a
100 degree day, why do you feel
cold?
• If you feel cold, it is because
your thermal energy is leaving
your body
• Corona of the sun example…
Presented by April Senger
Concept Check
• Suppose you apply a flame to 1 L of water
and its temperature rises by 3 degrees C.
If you apply the same flame for the same
length of time to 3 L of water, by how
much will the temp rise?
• 1 degree C
• When you touch a cold surface, does cold
travel from the surface to your hand or
does the energy travel from your hand to
the cold surface?
• It travels from hot to cold. Your hand to the
cold surface
Presented by April Senger
Thermal Expansion
• Thermal expansion results from the
molecules moving faster and apart in a
warm substance
• Where might some thing in our society
expand or contract?
• Bridges, railroads, buildings, dentists
• The Law of Conservation of Mass says that
matter cannot be created or destroyed
• The Law of Conservation of Energy says
that energy cannot be created or
destroyed
Presented by April Senger
Concept Check
• When you can’t loosen a metal lid on a
glass jar, how can you use the concept of
thermal expansion to rescue the
situation?
• Hold it under hot water to expand the lid
faster than glass
• A Concorde supersonic airplane is 20 cm
longer when in flight than when parked on
the ground. Why?
• Traveling at the speed of sound creates
great air friction and heat thus expansion
Presented by April Senger
What’s Up with Water?
• Water does contract until it reaches
about 4 degrees C
• If forms a unique crystal shape that
traps air between the molecules
making it less dense
• Below 4 degrees C, water begins to
expand again
• This is why ice floats
• Why is it so important that ice floats
on our lakes?
Presented by April Senger
Concept Check
• What is the coldest water at the
bottom of a frozen lake can be?
• 4 degrees C because it is the
most dense and will sink
towards the rocks
• Temps below 4 begin to expand
and range up to 0 near the ice
Presented by April Senger