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Thermal Energy
Chapter 16
Temperature – related to the average
kinetic energy of an object’s atoms or
molecules, a measure of how hot (or cold)
something is
 Thermal energy – the sum of the kinetic
and potential energy of all the atoms in an
object
– Thermal energy increases as
temperature increases
– At constant temperature, thermal energy
increases if mass increases


Heat - thermal energy that flows from
something at a higher temperature to
something at a lower temperature
Specific heat – amount of heat needed to
raise the temperature of 1kg of a material by
1 degree C or K
Specific Heat Equation
energy = (specific heat)  (mass) 
(temperature change)
energy = cmDt

Fahrenheit and Celsius are common scales
used for measuring temperatures.
On the Fahrenheit scale, water freezes
at 32ºF and boils at 212ºF.
• The Celsius scale, which is widely used in
science, gives a value of 0ºC to the freezing
point of water and a value of 100ºC to the
boiling point of water at standard
atmospheric pressure
Fahrenheit-Celsius Conversion Equations
A degree Celsius is 1.8 times as large as a
degree Fahrenheit. Also, the temperature at
which water freezes differs for the two scales
by 32 degrees.
TF  1.8t  32.0
TF – 32.0
t
1.8
TF = Fahrenheit temperature
t = Celsius temperature
The Kelvin scale is based on absolute
zero.
Absolute zero is the temperature at
which molecular energy is at a minimum (0
K on the Kelvin scale or –273.16ºC on the
Celsius scale).
Celsius-Kelvin Conversion Equation
T = t + 237
T = Kelvin temperature
t = Celsius temperature

Changes in thermal energy can be calculated
as change in thermal energy = mass X
change in temperature X specific heat
– When heat flows into an object and its
temperature rises, the change in temp is
positive
– When heat flows out of an object and its
temperature decreases, the change in
temperature is negative
 Calorimeter –used to measure specific heat
Conduction – transfer of thermal energy
through matter by direct contact of
particles
– Kinetic energy is transferred as particles
collide
– Solids, particularly metals, are good heat
conductors
 Convection – the transfer of energy by the
motion of heated particles in a fluid
– Transfer heat from warmer to cooler parts in
a fluid
– Create rain forests and deserts over different
regions of Earth


Radiation – energy transfer by
electromagnetic waves
– Some radiation is absorbed and some is
reflected when it strikes a material
– Heat transfer by radiation is faster in a gas
than in a liquid or solid

Most living things control the flow of heat by
using special features such as fur, blubber, or
scales

Insulator – material that does not let heat
flow through it easily
– Gases such as air usually make better
insulators than liquids or solids
– A vacuum layer in a thermos is a good
insulator because it contains almost no
matter to allow conduction or convection to
occur

conductor Any material through which
energy can be easily transferred as heat

Poor conductors are called insulators.
• Gases are extremely poor conductors.
• Liquids are also poor conductors.
• Some solids, such as rubber and wood, are
good insulators.
• Most metals are good conductors.

Heating systems – warm homes and
building
– Forced-air system – fuel heats air, which
is blown through ducts and vents; cool air is
returned to the furnace to be reheated
– Radiator system – hot water or steam in
a radiator transfers thermal energy to the
air
– Electric heating system – electrically
heated coils in ceilings or floors heat air by
conduction

Solar energy –
energy from the Sun
– Passive solar
heating - does not
use mechanical
devices to move
heat
– Active solar
heating - use solar
collectors to absorb
radiant energy,
which is circulated
through the building
Active Solar Heating System
 Heat
engine – an engine that
converts thermal energy into
mechanical energy
– Internal combustion engine – burns
fuel inside the engine in chambers or
cylinders
– ICE converts only about 26% of the
fuel’s chemical energy to mechanical
energy
Internal Combustion Engine
Machines operate with two energy
principles:
 The first law of thermodynamics states
that the total energy used in any process—
whether that energy is transferred as a result
of work, heat, or both—is conserved.
 The second law of thermodynamics states
that the energy transferred as heat always
moves from an object at a higher temperature
to an object at a lower temperature.

Air Conditioner
One example is an air
conditioner. An air
conditioner does work
to remove energy as
heat from the warm
air inside a room and
then transfers the
energy to the warmer
air outside the room.
Passive Solar Heating