What is the speed of sound? I mean, I know what it is, but how fast is it? And is it “local”? Is it relative to the medium through which it travels?
See, some friends of mine were at my pub. They were talking about the speed of sound and I was listening.
One guy was saying that the speed of sound is relative to the medium through which it travels. The other guy was saying that the speed of sound is like 700 mph no matter what, and that that’s the speed to break the sound barrier-in a jet for example.
The first guy was saying the second guy was wrong, and vice versa.
Who was right? I wasn’t about to open my big mouth cuz I had no idea. But I think that the first guy was right.
What’s the straight dope?
“Winners never quit and quitters never win, but those who never win and never quit are idiots.”
The speed of sound is dependant on the medium through which it travels. The speed of sound in water is much higher than the speed of sound in air. The speed of sound in a vacuum is 0.
I don’t have anything to cite offhand, but I can present a logical reason behind this. The speed of sound is basically how long it takes for each molecule along the path to bump into its neighbor and pass the sound wave along. The closer the molecules are together, the faster this happens. There are other factors as well, but density is the predominant one.
This principle comes into play in a number of places, such as layers of water with different densities distorting sonar signals.
Unfortunately, I no longer have any fluids textbooks lying around. I could go far more in depth, with all sorts of formulae and estimations for various altitudes (all in bizarre english system units) and so on until I look like a goddam know-it-all… well maybe it’s not so unfortunate.
Yes, and inside a neutron star where the density is 10^14 grams per cubic centimeter, the sound speed approaches the speed of light. IIRC, this happens when the neutron star is more than 3 times the mass of our sun. Hence that is how big a neutron star can be before it collapses into a black hole.
The speed of sound varies with the density of the air, depending on altitude, speed of sound at sea level is different then the speed of sound upper altitude… just dont push me for numbers, do a search for a thread I once posted on a skydiver breaking the sound barrier (this may be what the original question was on… dont know) lots of great sound barrier stuff in that thread. I will see if the search engine is working. and post if it is.
If you need a simple example next time you’re at the pub, think of the expression “having youur ear to the ground” which I guess derives from American Indians putting their ears on a railroad track to hear a train coming well before the sound wouuld reach their ears through the air.
The worst ones are where both sides are right, but aren’t listening to the other side.
The second guy was right, *if[/] his point was that ‘people breaking the sound barrier’ only refers to the speed of sound in air. Somehow I doubt he was insisting that the speed of sound in steel was the same as the speed of sound in air–but if he was, he was wrong.
Even if he meant it just in terms of ‘breaking the sound barrier’, a plane would have to go faster though air at 20 degrees to get a nice sonic boom than he would at zero degrees. Therefore “the speed of sound through air” is still not a defined value.
Even if you’re talking about Mach numbers, a Mach number is “a number representing the ratio of the speed of a body (as an aircraft) to the speed of sound in a surrounding medium (as air)” So “Mach 1” is not a universal value.
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The second guy was way wrong, I just didn’t have enough information to correct him.
He was actually saying that the speed of sound (“how fast you have to go to cause a sonic boom in a super sonic jet”) is always the same.
The second guy was saying no, a jet flying at sea level would have to go faster than a plane at 60,000 feet would, because the speed of sound is faster at sea level, and the air is denser and it is warmer.
So, this is what started all of this in the first place.
“Winners never quit and quitters never win, but those who never win and never quit are idiots.”