Any science text can tell you that the mechanisms of heat transfer
are conduction, convection, and radiation.
We have seen examples of each of these in the workshops.
You saw Paloma and some other students earlier in the series make
a pinwheel turn by placing it under a source of heat. It was,
of course, air that made the pinwheel turn. The air around a candle
flame or light bulb is heated and expands. The colder air in the
room falls (you notice this when you open a refrigerator in your
bare feet) to replace the less dense warm air and starts a circulation
process that is called convection. Convection is an important
heat transfer process in gasses and liquids. It is the reason
why radiators (they should be called convectors) are placed on
outside walls or under windows.
You also watched as Chuck placed a metal rod in the flame of a
blow-torch. The heat in this case is transferred along the rod
by conduction. You may have heard this term before related
to electricity. It turns out that, in general, things that are
good conductors of heat are also good conductors of electricity.
Conduction is important mostly in solids. When the atoms of the
rod absorb energy from the flame, they vibrate, and since the
atoms of a solid are all linked together, eventually that vibration
makes its way to the end of the rod. We rely on conduction to
transfer heat from the stove to the pot to the thing we are cooking.
If Chuck had kept the rod in the flame long enough, the part in
the flame would start to glow red. You may have noticed this if
you have watched a blacksmith, sat near a pot-bellied stove, or
even looked at the heating elements on an electric stove. Some
things even get white-hot like the filament of a light bulb. In
all cases, the atoms of the material are moving so quickly that
they release some energy in the form of light. But there is also
some "light" that we can't see. This infra-red radiation
is the heat we feel in front of a roaring fire. Infrared radiation
allows energy to be transmitted through air or even empty space.
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