Speed of light vs. Speed of Sound

I have a quick, and probably simple question.

Since I learned that the light was faster than sound, I have been under the
assumption that frequencies along the electromagnetic spectrum gradually
increase in velocity as they go from the 20 hz minimum for sound to the 428
THz in the light range, or the .211 miles per second speed of sound (at sea
level) to the 186,000 miles per second speed of light (ina vacuum).

However, I now read in Gary Zukav's "The Dancing Wu Li Masters" that the
velocity of light, 186,000 Mps, applies to all electromagnetic waves (Pg.
56). Is this a mistake in this book, or is this in fact true? I am stumped
by this, because in learning about radio transmission's, I have been told
that RF travels at the speed of light, which I have always thought to be
false, however, with this information, I could see how RF would indeed
travel at the speed of light. Nonetheless, if it is true that the whole
electromagnetic spectrum has the same velocity, how is it that sound is
different?

I appreciate any help, and feel free to ask for clarification,

Thank You,
Shane Strate

Dear Brother Strates:

"Brother Strates" wrote in message
news:LOEfd.21437$EZ.21032@okepread07...
I have a quick, and probably simple question.

Since I learned that the light was faster than sound, I have been under
the assumption that frequencies along the electromagnetic spectrum
gradually increase in velocity as they go from the 20 hz minimum for
sound to the 428 THz in the light range, or the .211 miles per second
speed of sound (at sea level) to the 186,000 miles per second speed of
light (ina vacuum).

However, I now read in Gary Zukav's "The Dancing Wu Li Masters" that the
velocity of light, 186,000 Mps, applies to all electromagnetic waves (Pg.
56). Is this a mistake in this book, or is this in fact true?

It is true. All light, in vacuum, travels at c.

I am stumped by this, because in learning about radio transmission's, I
have been told that RF travels at the speed of light, which I have always
thought to be false, however, with this information, I could see how RF
would indeed travel at the speed of light.

Light is NOT just visible light. Every finite frequency (from just above
0, to just "below infinity") is expected to travel at c.

Nonetheless, if it is true that the whole electromagnetic spectrum has
the same velocity, how is it that sound is different?

Sound isn't different, unless you exceed a certain power level (for example
the shock cone in front of a supersonic aircraft).

For visible light, in a medium such as air, glass, or water, the speed of
light is slowed (c_medium c). But for gamma rays, light with very high
energies, it travels at c regardless of what it is passing through.

David A. Smith

"Brother Strates" wrote in message
news:LOEfd.21437$EZ.21032@okepread07...
I have a quick, and probably simple question.

Since I learned that the light was faster than sound, I have been under
the
assumption that frequencies along the electromagnetic spectrum gradually
increase in velocity as they go from the 20 hz minimum for sound to the
428
THz in the light range,

It looks like you might think that sound is a low frequency electromagnetic
wave. Sound is a mechanical wave in air, kind of like the way a wave on the
ocean is a mechanical wave in water. Sound is oscillating air pressure. We
can hear it, if it oscillates with enough energy to vibrate our ear bones,
between appx 20 Hz and 20 kHz. Air will oscillate at higher and lower
frequencies, we just won't hear it. It is a completely separate phenomenon
from electromagnetic waves.

"N:dlzc D:aol T:com (dlzc)" N: dlzc1 D:cox wrote in message news:lhGfd.19533$SW3.8964@fed1read01...
Dear Brother Strates:

"Brother Strates" wrote in message
news:LOEfd.21437$EZ.21032@okepread07...

Nonetheless, if it is true that the whole electromagnetic spectrum has
the same velocity, how is it that sound is different?

Sound isn't different, unless you exceed a certain power level (for example
the shock cone in front of a supersonic aircraft).


Sound is not an electromagnetic wave at all. It is a
mechanical wave.

Martin Hogbin

"Brother Strates" wrote in message news:LOEfd.21437$EZ.21032@okepread07...
I have a quick, and probably simple question.

Since I learned that the light was faster than sound, I have been under the
assumption that frequencies along the electromagnetic spectrum gradually
increase in velocity as they go from the 20 hz minimum for sound to the 428
THz in the light range, or the .211 miles per second speed of sound (at sea
level) to the 186,000 miles per second speed of light (ina vacuum).

Sound and electromagnetism are two different things that both happen
to demonstrate wave behavior.

The speed of sound in air, for example, depends on the temperature but
not the frequency:
http://scienceworld.wolfram.com/phys...edofSound.html
so low frequency sounds (like those made by elephants or the wind at
less than 1 Hz) travel at the *same* speed as high frequency sounds
(like those made by Ultrasonic cleaners or dog whistles).


However, I now read in Gary Zukav's "The Dancing Wu Li Masters" that the
velocity of light, 186,000 Mps, applies to all electromagnetic waves (Pg.
56). Is this a mistake in this book, or is this in fact true?

The speed of electromagnetic radiation in a vacuum (usually called
simply the "speed of light") is the same for cosmic rays (with
wavelengths smaller than an atom) and for ultra-low-frequency Herzian
waves (with wavelengths thousands of km long).

I am stumped
by this, because in learning about radio transmission's, I have been told
that RF travels at the speed of light,

Correct.

...which I have always thought to be
false, however, with this information, I could see how RF would indeed
travel at the speed of light. Nonetheless, if it is true that the whole
electromagnetic spectrum has the same velocity, how is it that sound is
different?

It appears that the ignoramus who first introduced you to the idea
that waves have speeds failed to make clear to you that sound and
light are two completely different phenomena. Sound requires the
movement of matter, which has mass, while light involves the movement
of electric and magnetic fields, which have NO mass.

The comparison is therefore very limited.

"Analogies are like ropes. They tie things together well, but you
won't get very far if you try to push them." - Thaddeus Stout


Tom Davidson
Richmond, VA

Dear Martin Hogbin:

"Martin Hogbin" wrote in message
...

"N:dlzc D:aol T:com (dlzc)" N: dlzc1 D:cox wrote in
message news:lhGfd.19533$SW3.8964@fed1read01...
Dear Brother Strates:

"Brother Strates" wrote in message
news:LOEfd.21437$EZ.21032@okepread07...

Nonetheless, if it is true that the whole electromagnetic spectrum has
the same velocity, how is it that sound is different?

Sound isn't different, unless you exceed a certain power level (for
example
the shock cone in front of a supersonic aircraft).

Sound is not an electromagnetic wave at all. It is a
mechanical wave.

You are correct. However without changing medium properties, sound also
travels at a single speed, which is counter to the OPs apparent belief.

David A. Smith

I would like to add up more information about the difference between EM
waves and Sound waves:
Sound waves are pressure waves and have the characteristic of being
longitudinal, i.e., the direction of propagation is parallel to the
amplitude of the wave. Unlike EM waves (such as visible light) with the
characteristic of being transversal waves, i.e., the direction of
propagation is orthogonal (perpendicular) to the amplitude of the wave. In
addition, in a medium, both EM and Sound waves behave in opposite ways: EM
waves slow down in denser medium and this decrease in speed in measured by
the Optical Density of the material, called the index of refraction. In
Sound waves, however, the opposite happens. The denser the medium, the
faster the speed of sound. This makes a lot of sense since, as mentioned
above, sound waves are pressure waves. So we can hypothesize, at least
theoretically, that the speed of sound can indeed reach the speed of light
if the medium has an extremely large density. For example, in the Big Bang
Cosmology, workers in this field try to avoid the notion that the primordial
nucleus that caused the big bang had infinite density otherwise, the sound
would have been of infinite speed!

Cheers,
~Raja

Dear Raja Almukahhal:

"Raja Almukahhal" wrote in message
link.net...
I would like to add up more information about the difference between EM
waves and Sound waves:
Sound waves are pressure waves and have the characteristic of being
longitudinal, i.e., the direction of propagation is parallel to the
amplitude of the wave. Unlike EM waves (such as visible light) with the
characteristic of being transversal waves, i.e., the direction of
propagation is orthogonal (perpendicular) to the amplitude of the wave.
In
addition, in a medium, both EM and Sound waves behave in opposite ways:
EM
waves slow down in denser medium and this decrease in speed in measured
by
the Optical Density of the material, called the index of refraction. In
Sound waves, however, the opposite happens. The denser the medium, the
faster the speed of sound. This makes a lot of sense since, as mentioned
above, sound waves are pressure waves.

It only makes sense if the medium's compressibility is inversely related to
its density. If you have a dense, compressible medium, the molecules move
more slowly for a given temperature. Example would be helium compared to
air. The speed of sound in helium is higher than air.

So we can hypothesize, at least
theoretically, that the speed of sound can indeed reach the speed of
light
if the medium has an extremely large density.

You can drive the formula that way, but you will have left any "theory" far
behind. So "theoretically" is not correct.

For example, in the Big Bang
Cosmology, workers in this field try to avoid the notion that the
primordial
nucleus that caused the big bang had infinite density otherwise, the
sound
would have been of infinite speed!

At the instant of the Big Bang, it is believed by some that the speed of
light was effectively infinite. This would explain why no light from the
Big Bang is still visible.

And since the instant of the Big Bang had no matter, there was no medium to
transmit sound. Matter came some microseconds after the Big Bang, and
compressible media some many seconds later. (Well, since no one was
around... "expected" should be sprinkled in the last sentence.)

And since the Big Bang took place "everywhere at once", in a size of
perhaps millions of light years in "diameter", the density may have been
high, but it was not infinite. The CMBR is expected to have filled the
Universe at the time, and it is only a few tens of million light years
"thick" to provide the spectrum it does.

David A. Smith

Just for clarification may I recommend the site:
http://scienceworld.wolfram.com/phys...edofSound.html

Eq (1) gives the speed of sound in terms of the pressure and density
of a gas and gamma, the ratio of the specific heats (a function
primarilty of the geometry of the molecule).

The Ideal Gas Law can be combined with this to give Eq (4), which
relates the speed of sound in a gas to gamma, the temperature, and the
molecular weight.

For real mixtures of gases, these quantities should be averaged
separately.


Tom Davidson
Richmond, VA