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 Click here to return to the Physics Archives

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