January 6-7, 2011
What is the difference…
• Between a hot and cold cup of coffee?
• Temperature
• Temperature is a man-made, arbitrary scale
indicating which direction heat is flowing
Temperature
• Temperature: a measure of the AVERAGE
kinetic energy of the particles in a substance
• The molecules of hot coffee are moving faster
than the molecules of the cold coffee
• More Heat=More Thermal Energy=More
Kinetic Energy
Temperature
• Temperature measures the average kinetic
energy per molecule
• Liquids, solids, and gases expand differently
when heated.
• Thermometers use an expanding liquid to
measure temperature.
Physics in Action
• Which of the following is TRUE for the water
molecules inside popcorn kernels during
popping?
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Their temperature increases.
True
They are destroyed.
False
Their kinetic energy increases.
True
Their mass changes.
False
Gabriel Fahrenheit Simplified
• Fahrenheit took a glass tube and graduated
it…made marks: 1,2,3…etc.
• He used water as the standard. We often use
water as our standard for things-its cheap and
easy to get!
• He froze some water and the mercury in the
tube dropped to the mark he made…32
degrees. When water boiled the mercury in
the tube rose to 212 degrees.
Anders Celsius Simplified
• When Celsius investigated the subject of
temperature he did something a little
differently.
• He did not mark off the glass tube. He simply
put it into frozen water and where the
mercury landed he called that 0 degrees.
• When water was boiling and the mercury rose
and leveled off he called that 100 degrees.
• This is the one used most around the world.
What do I need to Know?
• Freezing point (Melting Point): 0*C/32*F
• Boiling point (Condensation Point):
100*C/212*F
Lord Kelvin Simplified
• Kelvin was interested in a more philosophical approach to the
behavior of matter at different temperatures.
• He wondered what would happen if there was a condition of NO
HEAT. At “absolute” zero, what would the conditions be?
• At zero Kelvin, at absolute zero, all motion would cease since
temperature is an indirect measure of the motion of molecules.
• So, if there was no heat there would be no motion and thus no
temperature.
• But a condition of absolute zero cannot exist since there is no
absolute NO motion.
• Everything moves relative to SOME frame of reference. So
everything has SOME temperature!
• Atoms vibrate. Electrons revolve around the nucleus of every atom.
• Everything moves relative to something.
Heat and Temperature
• Heat and Temperature are different.
• Heat is a type of ENERGY; measured in joules.
• All things are made of atoms and the atoms
are always moving.
• Heat: is the TOTAL l kinetic energy because of
ALL the atoms in an object.
Think about it…
Why does JELLO call for hot water?
The hot water has more internal energy
The molecules of the hot water have a higher
kinetic energy and therefore disperse the
coloring more quickly!
Check your Understanding…
• Which has more internal energy…a hot cup of
coffee or an iceberg?
The iceberg has more internal energy than the
cup of coffee because it is made up of a much
larger number of molecules!
Internal Energy
• Internal Energy: the energy of a substance
due to the random motions of its component
particles and equal to the TOTAL energy of
those particles
Why doesn’t a sparkler burn a
little kid?
A sparkler has a very high
temperature but a very small
amount of internal energy.
When Objects are Heated
• Materials expand when they are heated.
• This is because the increase in heat energy
makes the atoms move around more
• The atoms bounce into each other, moving
farther apart and the material expands.
• Hot objects=atoms move farther apart=expand
• When a material is cooled, the atoms move
together and the material contracts.
• Cold Objects=atoms move together=contract
Direction of Thermal Transfer
• Imagine a can of warm fruit juice immersed in
a large beaker of cold water.
• After about 15 minutes, the can of fruit juice
will be cooler and the water surrounding it will
be slightly warmer.
• Eventually, both the can and the fruit juice
and the water will be at the same
temperature.
Thermal Equilibrium
• Thermal Equilibrium: the state in which two
bodies in physical contact with each other
have identical temperatures.
• Which of the following are at thermal
equilibrium?
How do you know?
• A hot copper pan is dropped into a tub of water. If
the water’s temperature rises, what happens to the
temperature of the pan?
• The pan’s temperature decreases if the water’s
temperature increases.
• How will you know when the water and copper pan
reach thermal equilibrium?
• The water and pan have reached equilibrium when
their temperature are the same.
Phase Change
• 3 States of Matter: Solid, liquids, and gases
• Whether the substance is in its solid, liquid, or
gaseous state depends on the TEMPERATURE!
• Temperature is speed! (whole thing)
• Heat is speed AND mass! (each atom)
DRAW THIS!!!
-Gain energy
Loss of energy-
<0*C/32*F
>100*C
212*F
Solid, Liquid, or Gas?
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Water at 50*C
Liquid
Water at 120*C
Gas
Water at 10*F
Solid
Water at -5*C
Solid
Water at 100*C
Gas
Gain or lose energy?
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When water freezes?
Loses-got colder
When water boils?
Gains-got hotter
When ice melts?
Gains-got hotter
During condensation?
Loses-got colder
When water turns to steam?
Gains-got hotter
How Heat Travels
• Heat always transfers from hot to cold.
• Heat does not rise (hot air rises).
Check for Understanding
• You put ice into a cup of hot chocolate. The
ice gives its cold to the liquid. Yes or no and
why?
• If two cups of hot chocolate, one at 50*C and
the other at 60*C, are poured together in a
large container, which way did the energy
transfer?
• What will the final temperature of the double
batch be?
• A cup of hot tea is poured from a
teapot and a swimming pool is filled
with cold water. Which one has a
higher total internal energy?
• The water in the swimming pool has more internal
energy. The much larger volume, and therefore the
much larger number of particles, more than makes
up of the lower temperature.
• Which has a higher average kinetic
energy?
• The hot tea has a higher average kinetic
energy, because temperature is proportional
to average kinetic energy.
Lab Explanation