Transfer of Thermal Energy Name: ________________ Class: _________________ Index: ________________.
Thermal Energy Transfer Review 2012 13
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Transcript of Thermal Energy Transfer Review 2012 13
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The Movement of HeatHeat is thermal energy moving from a
warmer object to a cooler object. This
is known as thermal transfer.
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Heat Transfer Facts:
Heat always moves from a warmer
place to a cooler place
o Hot objects in a cooler room will cool toroom temperature
o Cold objects in a warmer room will heat
up to room temperature
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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.
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How is Heat Transferred?
Heat transfers in THREE ways:
Conduction
Convection
Radiation
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CONDUCTION
Heat is transferred from one particle of
matter to another in an object without the
movement of the object.
Conduction = CONTACT
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Have you ever
Touched a metal spoon sitting in a pan of boilingwater only to be surprised by hot HOW it is??
Think back to what you know about metals and
nonmetals. What conducts heat better? Metal
or Nonmetal? Why?
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Example of
Conduction
Think of a metal spoon in a pot
of water being heated.
The fast-moving particles of the
fire collide with the slow-movingparticles of the cool pot.
Because of these collisions, the
slower particles move faster
and heat is transferred.
Then the particles of the potcollide 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.
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Examples of Conduction
A piece of metal in a forge glows red as
heat is transferred to the metal from the
forge.
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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
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Metals are different
The outer e______ of metal atomsdrift, and are free to move.
When the metal isheated, this sea ofelectrons gain k_____energy and transfer itthroughout the metal.
Insulators, such as w___ and p____, do nothave this sea of electrons which is why theydo not conduct heat as well as metals.
lectrons
inetic
ood lastic
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Why does metal feel colder than wood, if they
are both at the same temperature?
Metal is a conductor, wood is an insulator. Metalconducts 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.
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CONVECTION
Convection is the movement that transfers heatwithin fluids (air and gas)
Heat is transferred by currents within the fluid or
gas
Convection = VENTS through air and liquid
particles
Convection moves in a circular pattern
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Examples of Convection: Have you ever noticed that the air near the
ceiling is warmer than the air near the floor? Orthat 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.
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Explaining Convection
Convection currents
cause the coolerbreezes you
experience by a
large body of water
These currents also
cause the
movement ofmagma within the
earth.
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Convection
What happens to the particles in a liquid or a
gas when you heat them?
The particles spread out andbecome less dense.
This effects fluid movement.What is a fluid?A liquid or gas.
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Water movement
Hot water
risesCooler
water sinks
Convection
current
Cools at the
surface
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Why is it windy at the seaside?
C ld i i k
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Cold air sinks
Where is thefreezercompartment
put in a fridge?
Freezercompartment
It is put at thetop, becausecool air sinks,
so it cools thefood on theway down.
It is warmerat the
bottom, sothis warmerair rises and
a convectioncurrent is
set up.
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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)
Th thi d th d f h t t f
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The third method of heat transfer
How does heat energy get
from the Sun to the Earth?There are no particlesbetween the Sun and the
Earth so it CANNOT
travel by conduction or
by convection.
?RADIATION
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Radiation Comes From Other Sources
Have you ever sat too close to a campfirewhile cooking marshmallows (enjoying the
warmth) only to notice that your skin is really
warm?
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Examples of Radiation
1. Fire2. Heat Lamps
3. Sun
R di ti
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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
C ti ti
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Convection questions
Why are boilers placed beneath hot watertanks in peoples homes?
Hot water rises.
So when the boiler heats the water, and the hot waterrises, the water tank is filled with hot water.
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.
R di ti ti
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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.
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Thermal Heat Transfer Quiz
How much do you know about thermal
heat transfer???
Show what you know!!
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1. Which of the following is not a
method of heat transfer?A. Radiation
B. InsulationC. Conduction
D. Convection
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3. How does heat energy reach
the Earth from the Sun?A. Radiation
B. ConductionC. Convection
D. Insulation
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Thermal Energy Transfer