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The speed of a material's molecules or
atoms determines their kinetic energy. Heat is the total
kinetic energy of an object. That heat can be
transferred to other materials through conduction,
convection and/or radiation.
Questions you may have about this are:
Heat energy can be transferred from one
substance to another when they are in direct contact.
The moving molecules of one material can increase the
energy of the molecules of the other. The heat can also
travel through a material as one molecule transfers
energy to a neighboring one. This type of heat transfer
is called conduction.
Conduction is mainly seen with solid
objects, but it can happen when any materials come into
contact, like when warm air is in contact with your
skin.
Some materials are better conductors of
heat than others. For example, metals are good
conductors of heat, while a material like wood isn't.
Metal heated on one end will soon be hot on the other
end too, while that is not true with a piece of wood.
Good conductors of electricity are often good conductors
of heat.
Since the atoms are closer together,
solids conduct heat better than liquids or gasses. This
means that two solid materials in contact would transfer
heat from one to the other better than a solid in
contact with a gas or a gas with a liquid.
When a gas or a liquid is heated, hot
areas of the material flow and mix with the cool areas.
This type of heating is called convection. Forced air
heating and air conditioning are examples of heating (or
cooling) by convection.
This is an effective way of bringing a
hot (or cold) fluid to a different area. Convection
transfers heat over a distance faster than by
conduction. But ultimately conduction must transfer the
heat from the gas to the other object.
A third method to transfer heat is by
radiation. A warm or hot object gives off infrared
electromagnetic radiation, which can be absorbed in
another object, heating it up. Electric heaters with the
shiny reflector use radiation to heat. If they add a
fan, they use both radiation and convection to heat an
area.
Transfer of heat by radiation travels at
the speed of light and goes great distances, even in a
vacuum. We are heated from the Sun through radiation
transfer of heat.
Atoms or molecules transfer kinetic
energy to their neighbors through collisions. When
objects are in contact this transfers heat by
conduction. Liquids and gases can move high or low
energy molecules to another region through convection.
Atoms can radiate energy that can energize a distant
atom, resulting in heat transfer by radiation. |
