TYPES OF HEAT TRANSFER
How does heat travel from one object to another?
By:
Conduction,
Convection and
Radiation.
RADIATION
Radiation is when warm or hot matter
gives off electromagnetic radiation that
is then absorbed by an object at a
distance without touching it. The object
becomes warm as it absorbs the heat.
THE SUN Heats the Earth!
Our atmosphere is largely heated from
below, by the Earth itself. First, the sun
heats Earth’s water, rocks, and soil.
Then, the heat from these things warms
up the layer of air closest to Earth’s
surface with radiant heat. That’s why
you’re warmer at the bottom of a mountain than when you’re standing at the
top. Also, since the air closer to Earth is denser, dustier, and moister than
air in upper layers, they are able to absorb more of the sun’s radiation, as
well as more of heat radiating from a warmed Earth. Can you think of how
this might relate to global warming?
Which other things radiate heat besides the sun?
Remember, these are things that heat other objects without touching them,
like light bulbs, campfires, radiating space heaters, running motors and
engines … what other things can you think of?
CONVECTION
Convection is how heat moves from one
area to another in liquids and gases.
For example, warm, moist air rises to
create clouds, while pushing down cold
air to Earth. Warm
ocean water travels
north and south from the
warmer regions and
pushes the cold water
around, creating
currents. You may notice
that when you open a window on a cold day, the warm air escapes (warm air
and water pushes around cooler air and water). Most ovens work by
radiating heat, but a convection oven (above left) works with hot air
currents.
CONDUCTION
Conduction is when objects or materials are touching the vibrating molecules
from the warmed object transfers this energy to the cooler object. For
example, a hot stove burner will transfer heat to the pot sitting on top of it,
which will then transfer heat to the water inside.
Conduction is the main way for heat to travel through solid materials.
All solid materials conduct heat, but some do a better job than others.
Generally, metals are good conductors while porous (material with plenty of
spaces between its molecules) materials are not. Styrofoam is a good
example of a poor conductor, but it’s a good
insulator. Good conductors of electricity,
such as metal wire (especially copper), are
usually good conductors of heat.
Some materials are better than others. This
man will feel more heat through the marble
tile than through the piece of carpet because
the carpet is more porous (full of air);
however, the carpet is a better insulator.
Check for Comprehension
Name and describe the three methods of heat transfer.
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Look up your answers to Question 4 in the last lesson. List your sources of
heat again and name the type of heat transfer that applies.
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Bonus Questions: What kinds of heat transfer do you see with the Galilean
thermometer? Use the back of this sheet, if necessary.
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