CHAPTER 6: THERMAL ENERGY
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Transcript CHAPTER 6: THERMAL ENERGY
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