CHAPTER 6: THERMAL ENERGY

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Section 1—TEMPERATURE AND HEAT
The temperature of an object is related to
the average kinetic energy of the atoms or
molecules.
These particles move quickly when hot
These particles move slowly when cold
↑ KE = ↑ TEMPERATURE
The SI unit for temperature is the Kelvin
(K)
Kinetic energy is energy in the form of
motion. KE depends on the mass and the
velocity of an object.
MASS—how much matter is in an object
VELOCITY—speed and direction of an object
All matter is made of tiny particles—atoms
and molecules.
Atoms make up molecules and are held
together by chemical bonds.
In all materials---solids, liquids, or gases,
these particles are in constant motion.
The sum of the kinetic and potential energy
of all molecules in an object is the thermal
energy of the object.
↑ SPEED of the molecules = ↑ KE
↑ DISTANCE (separation) = ↑ PE
Heat always flows from warmer to cooler
objects.
Examples—
 A cup of hot chocolate/your cold hands
 Warm air/cold stick of butter
Because the air in the room is a higher
temperature than the butter, molecules in
the air have more KE than the butter
molecules.
Energy is transferred from faster-moving
molecules in the air to slower-moving butter
molecules.
The butter molecules then begin to move
faster and the temperature of the butter
increases.
↑ temperature = ↑ thermal energy
(KE)
(KE + PE)
HEAT is THERMAL ENERGY that flows from
something at a higher temperature to
something at a lower temperature.
Example—CHAIR
Thermal energy from a person’s body flowed
to the chair and increased the temperature of
the chair.
Heat is a form of energy, so it is measured in
joules—the same unit that energy is
measured in .
Heat always flows from warmer to cooler
materials.
The amount of heat that is needed to raise
the temperature of 1 kg of some material by
1°C or 1 K is called the specific heat of the
material.
Specific heat is measured in joules per
kilogram Kelvin or J/kgK.
Compared to 1 kg of sand, the amount of
heat that is needed to raise the temperature
of 1 kg of water by 1 °C is about 6 times
greater.
So…the ocean water at the beach would have
to absorb 6 times as much heat as the sand
to be at the same temperature.
Because water can absorb heat without a
large change in temperature, it is useful as a
coolant.
A coolant is a substance that is used to
absorb heat.
Section 2—Transferring Thermal
Energy
Thermal energy travels as heat from a
material at a higher temperature to a
material at a lower temperature.
The transfer of thermal energy from matter
by the direct contact of particles is called
CONDUCTION.
Examples—making a snowball; drinking a cup
of hot chocolate
(DIRECT CONTACT)
***CONDUCTION occurs because all matter is
made up of atoms and molecules that are in
constant motion.
Heat can be transferred by conduction from
one material to another (SOUP TO SPOON) or
through one material (FROM ONE END OF
THE SPOON TO THE OTHER END).
Although, CONDUCTION can occur in solids,
liquids, and gases---solids usually conduct
heat much more effectively
Why do you think most cooking pots are
made of metal, but the handles usually are
not?
Silver, copper, and aluminum are among the
best heat conductors.
Wood, plastic, glass, and fiberglass are poor
conductors of heat.
One way liquids and gases differ from solids
is that they can flow. Any material that can
flow allows fluids to transfer heat in another
way—CONVECTION.
CONVECTION is the transfer of energy in a
fluid by the movement of the heated
particles.
Example—Earth’s atmosphere is made of
various gases and is a fluid. The atmosphere
is warmer at the equator than at the poles.
Also, the atmosphere is warmer at Earth’s
surface than higher altitudes.
These temperature differences create
convection currents that carry heat to cooler
regions.
Earth gets heat from the Sun, but how does
that heat travel through space?
***Almost no matter exists in the space
between Earth and the Sun, so heat cannot
be transferred by CONDUCTION OR
CONVECTION. Instead, the Sun’s heat
reaches the Earth by RADIATION.
Energy that is transferred by radiation is
often called RADIANT ENERGY.
Light-colored clothing---reflects more radiant
energy
Dark-colored clothing---absorbs more radiant
energy
A material that does not allow heat to flow
through it easily is called an INSULATOR.
Materials such as wood, plastic, and
fiberglass are good insulators and therefore,
are poor conductors of heat.
Gases, such as air, are usually better
insulators than solids or liquids.
A material that is a good conductor of heat,
such as a metal, is a poor insulator.
Air = good insulator, poor conductor
Building insulation is usually made of fluffy
material, such as fiberglass, that contains
pockets of trapped air.
 Reduces flow of heat between building and the
air outside
 Helps furnaces and air conditioners work more
effectively, saving energy
Section 3—Using Heat
What is the simplest and oldest heating
system?
Wood or coal burned in a stove
 Advantage—cheap
 Disadvantage—heat transfer to others
rooms is slow
 Most common--PHS
 Fuel is burned in a
furnace and heats air;
fan blows warm air
through ducts in each
room
 CONVECTION CURRENT
Closed metal container that contains hot
water or steam.
Fuel is burned in a central furnace and heats
a tank of water; pipes carry the hot water to
radiators that are located in each room.
 No central furnace
 Cost more than electric
heat pump
 Walls/floors not able to
include pipes/ducts
The energy from the Sun is called solar
energy.
Advantage—free, endless supply
Disadvantage—depends on
location/weather
 No mechanical devices
 House/building faces
the South (lots of
windows on the South
sunny side)
 Cheap
 Uses devices called
solar collectors; heat air
or water and then
circulate it through the
house
 Expensive
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