The speed of sound can change quite a
bit depending on what it is traveling through
(air, water, or even metal). The best way to
understand this is to know just what sound is.
When you talk or a when a stereo plays music
from a speaker, the air molecules nearby gets
pushed away into neighboring molecules and the
bumping continues in a wave much like when you
drop a rock into water and the waves travel away
in a circle. When the last air molecule
finally hits your ear, your brain tells you there
is a sound.
As for the speed, that depends on how quickly
the molecules vibrate and hit each other. Air
is a gas and there are relatively few molecules
per volume so the sound travels around 773 miles
per hour. Water is a liquid which is much
more dense than air and the molecules hit each
other quicker. So if you were under water and
someone hit two rocks together the sound would
reach you at a speed of 3349 miles per hour.
Finally, if you were to place your ear on a
railroad track which is made of steel and someone
tapped it with a hammer further down the track,
the sound would reach you at a speed of 11,185
miles per hour! That is very fast because
steel is a solid material and the molecules can
vibrate into each other very quickly.
So when fighter jets go faster than the speed
of sound, what they mean is the speed of sound in
air. This is called the
A jet traveling at Mach 2 is:
2 x 773 = 1546 miles per hour.
The fastest plane can reach speeds of 2193 miles
One last note. If you were in space you
would not hear anything. That is because
there is nothing in space that can vibrate to
transfer the sound. So the speed of sound in
space is 0.
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