SpaceShipOne in outer space video

Temperature and pressure and CDr

No, not temperature and pressure and CDr, just temperature.

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.

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.

but it is really hard to fly at any speed through solid steel :)

Is that digital or analog temperature?

Mario Perdue NAR #22012 Sr. L2 for email drop the planet

"X-ray-Delta-One, this is Mission Control, two-one-five-six, transmission concluded."

LOL!

But it can be done. It's called forging. :-) We do it every day with 2,500 ton presses.

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.

It is not both smoggy and humid in LA at the same time however.

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

not for sound it aint :-) I never said you needed to survive the experience :-)hehehe

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:

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:

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.

Right, it varies with the substance.

Not significantly.

It is at temperatures encountered in the usable atmosphere, that portion where "speed of sound" has some meaning.

Not if the temperature is the same.