Heat Transfer Review
Conduction, Convection and Radiation
The Movement of Heat
Heat is thermal energy moving from a
warmer object to a cooler object. This
is known as thermal transfer.
Heat Transfer Facts:
• Heat always moves from a warmer
place to a cooler place
o Hot objects in a cooler room will cool to
room temperature
o Cold objects in a warmer room will heat
up to room temperature
Question
If a cup of coffee and a popsicle were left
on the table in this room what would
happen to them? Why?
Answer: The cup of coffee will cool
until it reaches room temperature.
The popsicle will melt and then the
liquid will warm to room temperature.
How is Heat Transferred?
Heat transfers in THREE ways:
– Conduction
– Convection
– Radiation
CONDUCTION
Transfer of thermal energy from one
particle of matter to another in an object
without the movement of the object.
Conduction = CONTACT
• Think of a metal spoon in a pot
of water being heated.
• The fast-moving particles of the
fire collide with the slow-moving
particles of the cool pot.
• Because of these collisions, the
slower particles move faster
and heat is transferred.
• Then the particles of the pot
collide with the particles in the
water, which collide with the
particles at one end of the
spoon.
• As the particles move faster, the
metal spoon gets hotter. This
process of conduction is
repeated all along the metal
until the entire spoon is hot.
Example of
Conduction
Examples of Conduction
A piece of metal in a forge glows red as
heat is transferred to the metal from the
forge.
Conduction
When you heat a metal strip at one end, the heat
travels to the other end.
As you heat the metal, the particles vibrate, these
vibrations make the adjacent particles vibrate, and so on
and so on, the vibrations are passed along the metal and
so is the heat. We call this? Conduction
Metals are different
The outer e______
lectrons of metal atoms
drift, and are free to move.
When the metal is
heated, this ‘sea of
inetic
electrons’ gain k_____
energy and transfer it
throughout the metal.
Insulators, such as w___
ood and p____,
lastic do not
have this ‘sea of electrons’ which is why they
do not conduct heat as well as metals.
Why does metal feel colder than wood, if they
are both at the same temperature?
Metal is a conductor, wood is an insulator. Metal
conducts the heat away from your hands. Wood
does not conduct the heat away from your hands as
well as the metal, so the wood feels warmer than
the metal.
CONVECTION
• Convection is the movement that transfers heat
within fluids (air and gas)
• Thermal Energy is transferred by currents
within the fluid or gas
• Convection = VENTS through air and liquid
particles
• Convection moves in a circular pattern
Examples of Convection:
• Have you ever noticed that the air near the
ceiling is warmer than the air near the floor? Or
that water in a pool is cooler at the deep end?
• Examples: air movement in a home, pot of
heating water.
• Pick one of these examples and draw the
circular pattern in your notes.
Explaining Convection
• Convection currents
cause the cooler
breezes you
experience by a
large body of water
• These currents also
cause the
movement of
magma within the
earth.
Convection
What happens to the particles in a liquid or a
gas when you heat them?
The particles spread out and
become less dense.
This effects fluid movement.
What is a fluid?
A liquid or gas.
Fluid movement
Cooler, more d____,
ense fluids
sink through w_____,
armer less
dense fluids.
In effect, warmer liquids and
gases r___
ise up.
Cooler liquids and gases s___.
ink
Water movement
Cools at the
surface
Cooler
water sinks
Convection
current
Hot water
rises
Why is it windy at the seaside?
Cold air sinks
Where is the
freezer
compartment
put in this
fridge?
It is put at the
top, because
cool air sinks,
so it cools the
food on the
way down.
Freezer
compartment
It is warmer
at the
bottom, so
this warmer
air rises and
a convection
current is
set up.
RADIATION
• Radiation is the transfer of energy by
electromagnetic waves
• Radiation does NOT require matter to transfer
thermal energy
• Radiation = RADIATES (heat escaping the sun)
The third method of heat transfer
How does heat energy get
from the Sun to the Earth?
?
There are no particles
between the Sun and the
Earth so it CANNOT
travel by conduction or
by convection.
RADIATION
Examples of Radiation
1. Fire
2. Heat Lamps
3. Sun
Radiation
Radiation travels in straight lines
True/False
Radiation can travel through a vacuum
True/False
Radiation requires particles to travel
True/False
Radiation travels at the speed of light
True/False
Convection questions
Why does hot air rise and cold air sink?
Cool air is more dense than warm air, so the
cool air ‘falls through’ the warm air.
Why is the heating element placed near the
bottom of hot water tanks in people’s
homes?
Hot water rises.
So when the boiler heats the water, and the hot water
rises, the water tank is filled with hot water.
Radiation questions
Why are houses painted white in hot countries?
White reflects heat radiation and keeps the house cooler.
Why are shiny foil blankets wrapped
around marathon runners at the end
of a race?
The shiny metal reflects the heat
radiation from the runner back
in, this stops the runner getting
cold.
Thermal Heat Transfer Quiz
How much do you know about thermal
heat transfer???
Show what you know!!
1. Which of the following is not a
method of heat transfer?
A.
Radiation
B.
Insulation
C. Conduction
D. Convection
2. In which of the following are
the particles closest together?
A.
Solid
B.
Liquid
C. Gas
D. Fluid
3. How does heat energy reach
the Earth from the Sun?
A.
Radiation
B.
Conduction
C. Convection
D. Insulation
Your notes are complete
• JOURNAL REMINDER – you need a new
journal by next Monday!
• Glue in your completed heat transfer notes
now.
• Make sure to write today’s notes in your
table of contents
Vocabulary pages
• You will be handed a vocabulary page with
one of the types of heat transfer.
• Write the definition of the word you have
been given on the page.
• Next, draw a picture that demonstrates
(shows) what that words means.
Hint: think about how to explain this word to
someone who has never heard of it before.