Transcript The Transfer of Energy:

ENERGY
Conservation of Energy:
• The total amount of energy in a system remains
constant ("is conserved"), although energy within
the system can be changed from one form to
another or transferred from one object to another.
Energy cannot be created or destroyed, but it can
be transformed.
Energy
• Energy comes from the sun in the form of insolation.
• Insolation is INcoming SOLar radiATION
That energy is transferred by:
• Conduction
• Convection
• Radiation
• They may occur
individually, or all
three may occur at
once.
Lets start with conduction
• In conduction, energy is transferred between
substances by contact.
• Energy is transferred from high to low.
Therefore, when areas of higher temperature
come into physical contact with areas of lower
temperature, heat energy will be transferred.
The hot object will cool down and the cool object will
heat up until equilibrium is reached.
• However; (there’s always a catch . . .) More heat
is released from the warmer object than is gained
by the cooler object. – some heat energy escapes
into the surroundings during the process . . .
Examples of conduction:
On a cold day, warm air inside the
house comes in contact will cool air
outside and escapes from the house
~ that’s why we need insulation!
If an object is held in a flame (heat
energy); the heat from the flame will
travel down the object.
• In the atmosphere, heating by conduction is primarily
important at the ground, where air warms by directly
contacting the surface. Sunlight has very little
warming effect directly on air molecules.
Key Terms
• Rate of Change: Change in field value over
time; i.e. ~ how much has changed over
how much time.
• For example; If the temperature is 75o at
5:00 pm and 50o at 10:00pm, what would be
the rate of change?
• 75o - 50o (Change in field value)
5 hours (time)
• Rate of Change = 5o/Hour
A few more key terms. . .
• Calorimeter: Object used for measuring heat. (Heat can be
measured in ‘calories’, unrelated to dietetic calories.) A
calorimeter can be a thermometer, or any object used to
measure temperature.
• Potential Energy: Stored energy; higher temps mean higher
potential energy.
• Kinetic Energy: Energy of motion; more/faster motion
means higher kinetic energy.
Potential energy and kinetic energy are
interchangeable – items at rest (potential)
can move, items in motion (kinetic) can
stop.
The rock contains potential energy; if it
falls, it’s kinetic (and painful . . . )
Kinetic and Potential Energy in action via
conduction:
• The stored heat energy (potential energy) on the left is
being transferred to the cooler area on the right; once the
heat is in motion, it becomes kinetic energy.
Now, how about convection:
• Convection: The transfer of energy by circulation.
• Energy will circulate based on differences in density;
generally speaking, the higher the temperature, the lower
the density.
• Therefore;
higher temps tend to rise and lower temps tend to sink
Causing

 convective circulation
A few more key terms . . .
• Fluid: A substance with moderate density that
flows easily and assumes the shape of its
container.
• Earth’s Mantle: The portion of Earth between the
crust and outer core.
Convection in liquids:
Warm liquid (less dense)
rises, cool liquid (more
dense) sinks; the motion
creates convection cells
and/or currents.
Convection in air:
The air above the blacktop is
heated by the warm blacktop,
causing the air to rise. The
rising air is replaced by cooler
air from over the meadow.
So, we can figure that . . .
• Warm substances
(lower density) will
rise when placed into
cold substances
•
• Cold substances
(higher density) will
sink when placed in
warm substances.
Introducing heat causes density to decrease – thus air rises.
And, last, but not least . . .
Radiation
~ it’s all about the waves . . .
• Radiation is the transfer of energy through
space by waves.
• Not all radiation is the same, we receive and
transmit radiation in a variety of ways.
Absorption & Radiation of Energy
• Waves come in many shapes and sizes depending on a
myriad of factors.
• To keep it simple, short waves come from the sun and are
absorbed by the Earth. The Earth processes the radiation
(insolation) and re-radiates it back out as long waves.
• Absorption and radiation are dependent upon the
type of surface the waves encounter.
• Dark rough surfaces absorb more, therefore reradiate more.
• Whereas, light,
smooth surfaces
tend to reflect the
waves and thus reradiate much less.
Key Terms:
• Absorption: To take
in/retain energy waves
without reflecting.
• Black dirt, for
example, will retain
insolation like a
sponge retains water.
But, there are two sides
to everything. . .
• Reflection: To throw
or send back from a
surface.
• Water will reflect
insolation like a mirror
reflects an image.
• Re-radiation: To emit
or send off after
absorbing.
• The desert sand
absorbs short-wave
insolation all day, then
re-radiates long waves
back out.
• Radiative Balance: incoming = outgoing
• (insolation = re-radiation)
So . . .
• The rate at which energy is absorbed by a
surface is determined by its color and
texture.
• Dark, rough surfaces will absorb and reradiate much more than light, smooth
surfaces.
So; Now we know . . .
We transmit heat energy via:
• Conduction: Transfer
by contact
• Convection: Transfer
by circulation
• Radiation: Transfer
by waves