Negative. the speed of sound is a function of DENSITY. NOTHING else.
Temperature effects density and that is the only way that temperature
effects the speed of sound.
sound will travel through a shaft of solid steel at 70' faster than it will
travel through the same physical space of AIR at 70' and 1 ATM.
Density decides what the speed of sound is.
Chris Taylor
Um..
so..
Temperature has an affect on the speed of sound even though you said
density is the only function, and, um, temperature is related to
density, and um, temperature is, like density, a phyiscal property of
matter, and um, and nothing else? And, the speed of sound is a
function of density, and nothing else........
WHAT DO I WIN?! WHAT DO I WIN?!
Nice to have you back, Chris...
tah
You're wrong. The speed of sound in an ideal gas such as Earth's atmosphere
is a function of temperature and temperature alone. The speed is the square
root of the product of the ratio of specific heats (Cp/Cv), the ideal gas
constant, and temperature on an absolute scale. Since the only variable in
the equation is temperature it follows that the speed of sound is determined
by temperature alone.
In addition to pressure variances due to altitude, you also have its ability
to absorb water up to about 4% by volume. 4% = 100% humidity. (IIRC) Smog
also increases its density. So the speed of sound is much higher in LA on a
humid day. :-)
At a given specific pressure. However air is an irregular medium and
pressure varies at a specific altitude vs time just like clouds travel
around, wiffs of thick and thin air travel around. So while you are
"technically correct" there are practical considerations that superceed
it.
Jerry
Pardon the tech post.
that is like saying that the jet engine is a function of the speed of sound
since it lets you GO the speed of sound and is foolish logic.
temperature is irrevant and here is how to prove it.
you can have two objects at the exact same temperature and yet the speed or
sound through them WILL be different.
since we have removed temperature from the equation and yet still have a
difference we know temperature is NOT directly a factor. only indirectly in
that is can alter density. density is what directly affects the speed of
sound.
if you can alter density via temp fine. but its secondary. indirect.
density is the key.
thanks. very very busy :-( new jobs working 7 days a week :-(
Chris Taylor
Chris, you're confusing two different issues... you're talking about
differences in the speed of sound through different _kinds of materials_
(comparing liquids to gases) but the question - for purposes of describing
a "mach number" in flight - was about how the speed changes in the SAME
KIND of material, at different pressures and temperatures. How does AIR
change its speed of sound at different pressures or at different temperatures?
That turns out to be a quite separate question from the difference between
different kinds of material, as in comparing air to liquids or solids!
-dave w
Chris Taylor Jr wrote:
What's "irrevant"?
Same material?
Here's a link to the International Standard Atmosphere in tabular form:
formatting link
It shows selected properties at every 500 feet from the surface to 70,000
feet altitude. The properties shown are temperature, pressure ratio,
density ratio, viscosity ratio, kinematic viscosity ratio, and speed of
sound. If you examine the data, you'll see that temperature, density, and
the speed of sound decrease with altitude until you reach 36,089 feet. At
that altitude temperature becomes a constant -56.3 degrees C to the end of
the data at 70,000 feet. (This tab ends at 70,000 feet, others go much
further. The temperature in the ISA remains a constant -56.3 until about
82,500 feet where it begins to increase with altitude.) Note that the speed
of sound also stops decreasing at 36,089 feet, where it becomes a constant
295.1m/s to the end of the data at 70,000 feet. Note also that density does
NOT stop decreasing at that altitude, it continues to decrease beyond the
end of the data at 70,000 feet.
So, Chris, if the speed of sound in the atmosphere is, as you so vehemently
insist, a function of density and nothing else, then why does the speed of
sound remain constant from 36,089 feet to 70,000 feet (and beyond) while
density is decreasing? Why does the speed of sound become a constant
between the altitudes where temperature is also a constant if the speed is
not a function of temperature?
An ideal gas is a gas that obeys the ideal gas law. Your next question will
of course be, "What is the ideal gas law?" Here's a link that explains it
better than I can in this forum:
formatting link
In deriving a formula to calculate the speed of sound pressure and density
are encountered and the speed of sound can certainly be calculated using
them. The speed of sound can be expressed by multiplying the ratio of
specific heats (Cp/Cv) by pressure, dividing by density, and taking the
square root of that result.
The ratio of specific heats appears so frequently in fluid dynamics
equations that it is given a symbol of it's own, usually the Greek letter
gamma. For air at normal conditions both Cp and Cv are constants, hence
gamma is a constant. (For air gamma is 1.4.)
So now our equation is a bit simpler; the speed of sound is expressed by the
square root of gamma*pressure/density.
However, for an ideal gas, such as air at normal conditions in the
atmosphere, pressure and density are related through the equation of state;
pressure = density*R*T, where R is the ideal gas constant and T is
temperature on an absolute scale. Shuffle that equation a bit and you have
pressure/density=RT. Now, refer back to our previous equation for the speed
of sound, pressure/density appeared there too. We can now substitute RT for
pressure/density in that equation, and we have an equation for calculating
the speed of sound in an ideal gas that is dependent on just one variable,
temperature.
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