Thermal Energy
Chapter 6 – 2
Transferring Thermal
Energy
Objectives
• Compare and contrast conduction,
convection, and radiation.
• Compare and contrast conductors
and insulators.
• CLE 3202.2.3 Examine the applications and
effects of heat energy.
Heat Transfer
• Heat flows from hot to cold.
• If you hold something cold, heat
flows from hand to object.
• If you hold something hot, heat
flows from object to hand
A. Conduction
• Conduction – transfer of thermal E
through matter by direct contact of
particles. (particle to particle).
Particles collide with each other.
Cont.
1.Kinetic energy is
transferred as particles
collide.
2.Solids, particularly
metals, are good heat
conductors.
Conduction
• Heating of metal pan• Particles in handle of pan move slowly
• Fast moving particles from the bottom bump into slower
particles and speed them up
• Occurs until all particles move the same speed
3. Conduction works best in solids- especially metals- because
particles are close together. Metals- good conductors-because
electrons move easily & transfer KE to nearby particles
Conduction
• Conduction occurs in
all states of matter.
B. Convection
• The transfer of heat
energy by the
movement of heated
particles in a fluid is
called convection.
1. Fluids can be a gas or liquid
– any material that flows.
Cont.
2. Convection currents
transfer heat from warmer
to cooler parts of a fluid.
3. Convection is the transfer
of heat by bulk movement,
(a group of particles moving
from one place to another.)
4. The heated particles
move from one location
to another, bringing their
energy with them
Convection
Hot water
rises, cools,
and falls.
Heated air
rises, cools,
and falls.
Convection
• Convection-results in changes in
density
–As particles move faster, they
get farther apart
–Fluid expands as temperature
increases
–Larger volume = less density
–Less density results in the rise
of the warmer fluid
Lava LampCool oil = dense = sits
on the bottom
Warmer oil = less
dense than alcohol &
rises
As it rises, it loses
energy through
conduction
Causes decrease in
density = sinking
• Oil is warm,
so it rises –
• Convection
current
Conduction
occurs when
heat is
transfered
from the
warm metal
to the oil
Oil starts to
lose heat and
falls
Radiant energy is
produced by the
light bulb causing
the metal to warm
C. Radiation
• Radiation –
energy transfer by
electromagnetic waves.
Radiation
1. Radiant energy passes through the SPACE
BETWEEN particles, and is therefore,
more easily passed through gases.
2. Examples include: heating your hands by a
campfire, the sun heating the earth.
C. Radiation
3. Radiation does NOT need a
state of matter to flow
through.
4. Transfer of heat to the earth – occurs through
radiation. The waves travel through space even
without matter
Radiation
• 5. When radiation
strikes a material,
some energy is
absorbed, some is
reflected, and some
may be transmitted
through the material.
6. Dark colors absorb
radiant energy.
Light colors reflect
radiant energy
Cont.
7. Heat transfer by radiation
is faster in a gas than in a
liquid or solid.
8. All heat created by a light
source is radiant energy.
Thermal energy transfer
• Radiant Energy – Energy transfer by radiation
• When radiation strikes a substance:
• Some energy is absorbed
• some is reflected
• some is transmitted through the material
• Amount of energy that is absorbed, reflected and
transmitted depends on:
• Type of material
• Dark absorb more energy than light
Radiation
D. How do living things
control the flow of heat?
• Most living things control
the flow of heat by using
special features such as
fur, blubber, or scales.
E. What are insulators?
• Insulator – material
that does not let heat
flow through it easily.
Cont.
1.Gases such as air
usually make better
insulators than liquids
or solids.
Cont.
2. A vacuum layer in a
thermos is a good
insulator because it
contains almost no
matter to allow
conduction or
convection to occur.
Discussion Question 2
• What state of matter
generally makes a good
heat conductor? Heat
insulator?
Answer
• Solids generally conduct
heat better than liquids or
gases.
• Gases usually make better
insulators than liquids or
solids.
Pop QUIZ:
1. This is the transfer of heat by particles bringing their
energy from one location to another.
2. This type of transfer occurs more easily through gases.
3. This is the type of heat transfer that occurs in liquids.
4. This is the transfer of heat by particles colliding with
one another
5. This is the transfer of heat energy by electromagnetic
waves.
6. This is the type of heat transfer that occurs in solids.
Objectives
• Compare and contrast the transfer
of thermal energy by conduction,
convection, and radiation.
• Compare and contrast conductors
and insulators.
• CLE 3202.2.3 Examine the applications and
effects of heat energy.