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Traveling Sound
Name: walt
Status: other
Age: 60s
Location: N/A
Country: N/A
Date: 1999
Question:
When in school, I learned that the speed of sound is 1090
ft/sec. Is this what is known as 'mach'. Does this speed vary with
temperature, atmosphere, and/or other variables. By how much does it
vary, and is 'mach' a constant number, or does this vary also? Thanks,
Replies:
Mach is what is know as a dimensionless number. There are no units (i.e.
ft/sec) when you mention a mach number. Mach number is defined for
different areas of interest (i.e. fluid flow, aeronautics, etc.), but the
way you mean it, it is defined as the velocity of an object divided by the
velocity of sound. That means that if you divide velocity by velocity, the
units cancel out and the number is dimensionless. There are a large amount
of dimensionless numbers used for thermodynamics, heat flow, fluid flow,
plus others. As for the velocity of sound, yes it is dependant on other
things. Sound flows through a medium by basically bumping molecules. So
depending on the temperature of the of the air and the amount of air, your
speed of sound will be different. That is why there are different speeds of
sound at different altitudes. Mach numbers are a way of normalizing the
speed of an object to the speed of sound. Hope this helps.
Dr. C. Murphy
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Update: June 2012
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