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4 Methods of Thermal Energy Transfer

This prezi explains the basics of the four methods of thermal energy transfer.
by

Victoria Gorman

on 27 January 2017

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Transcript of 4 Methods of Thermal Energy Transfer

When a pot of water is on the stove, the bottom layer of water is heated by
conduction
. Then, the process of
convection
spreads the heat throughout the rest of the water.
Three Methods of
Heat Transfer
Radiation
Conduction
Convection
But what mode of transfer makes the water hot in the first place?
Here's convection in
water on a larger scale.
Normally, we think of convection happening in a "fluid" (liquid or gas). But, a special type of convection happens inside the Earth.

Heat generated by
radioactive decay in the core
causes the rocks in the mantle to move.
When the mantle "moves" what else do you think moves with it?
Convection
Four Methods of Heat Transfer
Radiation
is both a form of energy (radiant energy) and a type of energy transfer.
Radiation can travel through a
vacuum
(e.g. space.)
During energy transfer, the object emitting the radiation (e.g. the Sun) is not in contact with the object that is absorbing the radiation. (e.g. the Earth.)
Gases are usually
not
good
conductors
of heat. Liquids are better conductors than gases, but not as good as solids. This is because of the distance between atoms and molecules in gases and liquids.
Because of this, heat transfer in gases and liquids is accomplished in a unique way called
convection.
During convection, a part of the gas or liquid is heated and then the heat is spread throughout the rest of the "
fluid
" by motions of the fluid itself.
Convection is generally confined to liquids and gases.
There is an exception to this, which we will discuss later.
Heat is
conducted

within
an object or a substance.
Heat is also
conducted between
substances/objects that are in direct physical contact with one another.
During the process of
conduction
, kinetic energy is transferred between molecules or atoms when they collide with each other.
The heat excites the molecules in one place, starts them moving, and the kinetic energy is conducted from that place to another.
Conduction can occur between solids, liquids, and gases.
When conduction occurs
within
an object, we normally think about solids.
Conduction
Convection
Radiation
Radiation
Convection also applies to air. Remember air (gas) is considered a fluid.
What do you think the
horizontal movement of air
during convection is called?
When the mantle moves, what else do you think moves?
When we think of radiation, we normally think of the sun's rays.
In addition to the three forms of electromagnetic radiation found in sunlight, there are several other forms, as well.
This diagram shows what happens to solar radiation when it reaches Earth.
Conduction
The
Kinetic Theory of Matter
states all matter is composed of atoms or molecules that are in constant motion.
The energy represented by this motion is called
kinetic energy
(the energy of motion).
Temperature
is a measurement of the average kinetic energy (energy of movement) of the atoms or molecules in an object or system and can be measured with a
thermometer
.
During conduction, the molecules on the hot side are moving faster than normal. A chain reaction begins where the hotter molecules bounce into the colder molecules causing them to move faster. This process continues until the heat has been transferred to the cold side.
4 Methods of Thermal Energy Transfer
There are a few different forms of radiation.

Our focus is on the form called electromagnetic radiation, also known as electromagnetic energy (EM).

The sun's rays travel to Earth in the form of
electromagnetic radiation (EM)
. EM energy travels in waves.
In addition to traveling through a vacuum, these waves can also travel through gases, liquids, and solids.
Electromagnetic radiation can be
reflected, scattered, absorbed, or transmitted.
Solar radiation consists mainly of three types of electromagnetic radiation.
Infrared radiation (IR)
is invisible; yet we can feel it as heat.
Visible light
is the radiation we see as visible light; visible light can also make us warm.
Ultraviolet or UV radiation
is the invisible high-energy radiation that is needed in small amounts so the body can produce Vitamin D. In higher doses, it can cause cancer and eye damage. We don't feel UV rays as heat.
Time for notes:
Temperature
=Measurement of average molecular kinetic energy in a substance or an object.
Heat
=The energy moving between objects.
Thermal energy (heat energy)
moves from warmer to cooler.
The
greater the difference
in temperature of the two objects/substances, the
faster
the heat transfer.
Heat transfer
continues until
both objects have reached the
same temperature
(same average molecular kinetic energy).
Time for notes:
Four
types of heat transfer
Conduction, convection, radiation, latent heating
Conduction
- heat transfer between objects touching or within an object
Convection
- heat transfer throughout fluids (gases and liquids)
Radiation
- heat transfer between objects not touching, energy travels in waves and can travel through a vacuum (space)
Latent Heating
- stored energy in water vapor is carried away from Earth's surface and transferred to cooler air in the atmosphere.
Time for notes:
Radiation is both a form of energy (radiant energy) and a type of heat transfer.
During this transfer, the object giving off the energy is not in contact with the object receiving the energy.
Radiation can travel through a vacuum, solid, liquid, and gas.
Solar energy (solar radiation) travels as electromagnetic radiation.
Electromagnetic radiation (ER) has many forms.
All of the forms of ER travel as energy waves.
ER waves can be reflected, refracted, or absorbed.
The main types of ER in sunlight are: Ultraviolet (UV) - can't see or feel; Infrared (IR) - can't see, but we can feel as heat; and visible light, which as the name implies, we can see.
Large doses of UV can cause tissue damage.
The ozone layer of the Stratosphere - 2nd layer of the atmosphere - absorbs harmful ultraviolet rays.
Time for notes:
Only a small amount of total
solar radiation
reaches the Earth.
Of that small amount, only 51% of incoming solar radiation is absorbed by oceans and land.
Once absorbed, the EM radiation is converted to
thermal energy (heat energy)
The warmed ground and water heat the air above them.
Earth's surface radiates the heat energy back up towards space.
Some of the heat is trapped by
greenhouse gases.
The
Greenhouse Effect
is what maintains a livable temperature on Earth.
Heat transfer by
latent heating
is an important part of the weather and the water cycle.
Time for notes:
During
convection
, the heated fluid is pushed up by cooler fluid, spreads out, cools, and sinks.
In the
ocean
, sinking cooler water pushes water back up to the surface. This
surface water becomes warmed by the sun.
The
horizontal
part of convection in the ocean
creates currents
.
The
horizontal
part of convection in the air
creates wind
.
Convection can occur
locally or globally
.
A
special type of convection
occurs in the
mantle
. This convection
moves
Earth's
tectonic plates
.
Time for notes
(Conduction)
:
Conduction is a type of heat transfer that occurs when
objects are touching
. It can also happen
within
an object.
Conduction
can occur between solids, liquids, and gases
.
However, we usually think of conduction happening
within
solids.
The hotter molecules move faster (have a higher kinetic energy), bump into the cooler molecules, make them move faster, and they become warmer.
Heat transfer
is always from
hot to cold.
If two objects/substances have different temperatures, and they are brought into contact with one another, energy is transferred between the two. This energy in motion between the two objects/substances is called
heat (thermal energy)
.

Thermal energy is always transferred from the
warmer object (which has a higher temperature) to the cooler one (which has a lower temperature).
The greater the temperature difference, the
more rapid
is the rate of thermal energy (heat) transfer.

Heat transfer
will continue until both objects have reached the
same temperature
. In other words, the molecules have reached the
same average kinetic energy
.
A
vacuum
is any area that has no matter in it (this scientific term has nothing to do with the vacuum you use to clean a carpet).
Although Space has some matter, the matter is so "
rarefied
", Space often behaves like a vacuum. (use the context of the above sentence to determine the definition of "rarefied.")
Convection occurs because of differences in density. Fluid is warmed. The warmer "fluid" becomes less dense compared to the surrounding fluid. It is then pushed up by the cooler, surrounding fluid. The rising liquid or gas spreads out, cools down, and eventually sinks back down. The sinking fluid forces other warmer fluid up and the process continues.
One more thing...
The title of this Prezi is " 4 Methods of Thermal Energy Transfer," but we've only learned about three. Where's the fourth???

The diagram you just studied talks about "
latent heating
."
When enough energy is added to liquid water, it turns into water vapor. The molecules of water vapor contain a lot of energy. The water vapor becomes part of the atmosphere. The water vapor molecules move upward with the air molecules when areas of warm air get pushed up by areas of cooler air.
At some point, the air spreads out and cools. Remember, heat transfer is from warmer to cooler. The stored energy in the water vapor molecules, now moves into the cooler air. The water vapor turns back into a liquid (and usually forms a cloud), and the cooler air becomes warmer. Heat has been transferred.

Wind can also take the water vapor to other areas on Earth. Remember, weather spreads water and heat around the Globe?
In science terms, a
fluid
is a
liquid
or a
gas.
Let's look at an
example of convection
.

We've all boiled water on the stove.
The winds shown here are
"global"
winds.
As you can see there is vertical movement during convection, as well as horizontal movement.
Notice the horizontal part of convection has something to do with deep ocean currents.


If you said "
wind
", you'd be correct!!
These are
local
winds.
This is convection on a really LARGE scale.


The horizontal movement of air during these convection cells are called
global
winds!!
The shallow ocean currents have more to do with wind than convection.
The continents move!!
But, are the continents the only part of Earth that's moving?
Here's a list of the major forms of electromagnetic energy.
Radio Waves
TV waves
Radar waves
Infrared (We feel as heat when we absorb the energy.)
Light
Ultraviolet (This is what causes sunburns and skin cancer.)
X-rays (Just like the kind you get at the doctor's office.)
Short waves
Microwaves (Like in your microwave oven.)
Gamma Rays
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