Sound versus Heat
I was thinking about heat and sound. I thought about the way
they vibrate and at first could not see the difference. I am guessing that
heat is the vibration of an individual molecule and sound is the vibration
as a whole mass. What is the difference?
Your guess is pretty good, but I would like to clarify a little.
"Heat" refers to the energy contained in a body due to changes in
temperature, and temperature is an aggregate measure of vibrations
among molecules (both intra- and inter-molecular). These vibrations
are essentially random with respect to each other. Sound waves are not
random movements -- they are non-random pressure waves that move
through materials. Sound waves have measurable, characteristic
amplitude, wavelength, and frequency. The size and time scales of
sound waves' vibrations are much, much larger than thermal vibrations.
Hope this helps,
Heat is an electro-magnetic (E-M) wave, like a radio or TV signal.
Visible light is also an E-M wave.
Heat is an E-M wave in the Infra-red (IR) area of the electromagnetic
You see IR lights keeping food warm in restaurants.
IR wavelengths range from 1 millimeter (mm) (one one thousandth of a meter)
to 1 micrometer (um) (one one millionth of a meter).
The frequencies range from 300 GigaHertz (GHz) (10 to the 9th power) to more
than 10 to the 14th power Hertz.
The heat in your microwave oven is generated by a magnetron that creates an
electron-magnetic (radio) wave at 2.45 GHz to heat the food in the microwave
Sound is a pressure wave in the air. (It is referred to as an acoustic
That is the air experiences places of compression and places of less
compression, like a wave in a pond of water.
The old experiment is to put a ringing electric bell under a glass jar then
evacuate all the air out of the glass jar
and you will not be able to hear the bell ringing after all of the air is
The heat of the sun (and the light) passes through the vacuum of space to
warm our planet.
To read more, check out Wikipedia at:
Here is a whole bunch of charts:
or just "Google" "Electro Magnetic spectrum".
In electric speaker systems, acoustic waves are converted to electrical
"acoustic frequency" 10 Hz to 20 KiloHertz (KHz) (10 to the 3rd Power
Hertz). Electrical audio systems produce signals at a high of 20 KHz
because the human ear cannot hear frequencies above 20 KHz.
Good luck in your pursuit of scientific knowledge.
You are on the right track, but it is a bit more complicated. "Heat" is the
random motion of molecules, whereas "sound" is the compression and
rarefaction of molecules. This alteration can be in the direction of motion,
or perpendicular to the direction of motion, but in either case groups of
molecules move together with one another. Things get more intricate because
a "detonation" is both heat and in a sense "sound" if the energy of the
detonation is large enough. And the behaviour of molecules in solids,
liquids, and gases is different. But that gets beyond the scope of a service
like NEWTON. There are a number of websites and books on sound that presents
all the details. I would refer you there.
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Update: June 2012