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speed of sound

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  • 14-04-2007 8:03pm
    #1
    fuinneamh
    Registered Users Posts: 134 ✭✭


    Doing leaving cert physics, and theres one thing i can't get around, the speed of sound increase with density of a medium and the speed of sound increases with temperature in a gas. these two things seem to contradict each other as a hotter gas is less dense than a cooler one with all other things being equal. When i asked my teacher she stutterd for a few mins and then said you don't need to know and went onto the next topic. So any help would be appreciated.


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    #2
    Mellor
    Registered Users Posts: 39,043 ✭✭✭✭Mellor


    fuinneamh wrote:
    Doing leaving cert physics, and theres one thing i can't get around, the speed of sound increase with density of a medium and the speed of sound increases with temperature in a gas. these two things seem to contradict each other as a hotter gas is less dense than a cooler one with all other things being equal. When i asked my teacher she stutterd for a few mins and then said you don't need to know and went onto the next topic. So any help would be appreciated.
    http://en.wikipedia.org/wiki/Speed_of_sound#Speed_in_ideal_gases_and_in_air

    Temperature also affects the speed of sound, to a greater extent than density, air pressure has an effect in a gas too.

    and strictly speaking its stiffness that causes the speed of sound to increase, not density. density causes it to decrease if the stiffness is equal, but it normally isnt


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    #3
    Fallen Seraph
    Registered Users Posts: 443 ✭✭Fallen Seraph


    Intuitively it makes sense if you think about it on an atomic scale. Sound travels as compressions and rarefactions in a gas and these compressions and rarefactions are caused by pressures. Pressure itself, in terms of gas, is essentially atoms hitting into things. So when a gas is more dense the atoms have less distance to travel before they hit into the next atom and so the pressure differences move along faster. Also, when the gas is hotter the atoms are moving faster and as such will, again, take less time to hit into the next atom. (this explanation might, however, be taken with a grain of salt; it's just my intuition speaking, and what I've said seems to contradict mellor a little, so I could be wrong)


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