Sonic Boom

Another question for phycisists:

If an object that makes no noise flights faster than the speed of sound, does it make a sonic boom?

[shanek]

My understanding is yes. The compression of air faster than the speed of sound is what makes the waves. A whip crack is a sonic boom, although otherwise the whip makes little noise as it goes through the air. Light makes no noise, yet lightning creates a sonic boom.

[Goshawk]

Yes. Sonic booms are caused by shock waves in the atmosphere; it doesn't have anything to do with how much noise the object in question is making by itself (I presume you're talking about engine noise).

http://www.af.mil/news/factsheets/Sonic_Boom.html

[Walter Wayne]

How would something make a no noise flight. If you are moving through the air, you are displacing air in front and therefore must make some compression and rarefactions of the air. Thus noise. I think 0 noise flight is impossible.

Walt

And I agree with you, Walt.

Thank you guys, you have been enormously helpful

Oh, dog, I love this forum!!

[CurtC]

gabriel, you're suffering under the very common misconception that a sonic boom is the plane's own noise that gets "stacked up" in front because it can't get out of the way fast enough. That's not really how it works.

A sonic boom is the three-dimensional equivalent of the two-dimensional bow wave from a moving boat. The boat makes a bow wave if it's moving faster than the speed of the waves on the water, just because it's displacing water. It doesn't have to be creating its own noisy waves, the fact that it displaces water and is moving faster than the waves give you a bow wave.

In fact, that was a question raised to me by a woo woo in a UFO forum. It sounded like crap to me, by didnt know precisely why (I have just school grade physics).

I like a lot the boat/bow example. Makes it more clear.

[Crossbow]

Just throw in my sound, scientific opinion.

Yes it would since sonic booms are caused by a sudden compression of the air.

If an aircraft could travel without sound and if it could somehow break the speed of sound without actually causing any disturbance in the air, then yes it would be possible for that aircraft to break the sound barrier without generating any noise.

But practically speaking, those are impossible conditions to meet.

I hope this helps!

[Tez]

photons and muons travel fine through the atmosphere at > 330m/s, and neither make sonic booms.

Science is really an endless game of quibbles...

[neutrino_cannon]

About whips and the sound barrier :

http://www.straightdope.com/mailbag/m971210b.html

towels, however

http://www.straightdope.com/mailbag/mtowelsnap.html

Straightdope's cecil isn't our cecil, right?

[Skeptoid]

Straightdope's cecil isn't our cecil, right? Right, "our" Cecil was probably born around the time Cecil Adams started doing the Straight Dope column. (1973)

[richardm]

Originally posted by gabriel
In fact, that was a question raised to me by a woo woo in a UFO forum. It sounded like crap to me, by didnt know precisely why (I have just school grade physics).

I like a lot the boat/bow example. Makes it more clear.

If it's a UFO woo woo, you might like to raise the case of a large meteor that came trundling down the East Coast of Britain some years ago (possibly 1987ish, I think). It left a sprinking of meteoritic dust over everything, and also caused a sonic boom so loud that it had everyone who lived on our street out to see if the local ICI plant had finally blown up.

[garys_2k]

Yeah, sure, but meteors can't tap into the unlimited vacuum energy all around us and use it to shield gravity and destroy inertial effects. Sheesh! Get caught up on your woo-woo science, would you? :D

[scotth]

Originally posted by Tez
photons and muons travel fine through the atmosphere at > 330m/s, and neither make sonic booms.

Science is really an endless game of quibbles...

Since photos (light) or subatomic particle neither displace the atmoshpere as they pass though it, it could hardly be called a quibble.

If this was a stab at the effectiveness of scientific investigation or accuracy, it was a very poor one.

You would not know a muon exists except for serious scientific research.

[Crossbow]

And I would like to add, that my first comments contained a caveat about 'aircraft' since the orginal question regarded UFOs.

I deliberately avoided mention of sub-atomic particles and photons because they are far, far, far to small for an individual to actually travel in.

[Ladewig]

Light makes no noise, yet lightning creates a sonic boom.

Thunder is not a sonic boom. The sound of thunder is created when the air around the lightning bolt is compressed very rapidly by the heat of the lightning (tens of thousands of degrees).

[Soapy Sam]

How big must an object be, to make a sonic "boom"?
Do very small, very fast objects (eg a squirrel, ductaped to a small rocket), make a sonic "pop"?

[shanek]

Originally posted by Ladewig
Thunder is not a sonic boom.

Not according to these sources:

http://www.pbs.org/wgbh/nova/barrier/boom/choice2.html
http://www.abc.net.au/science/k2/moments/s512994.htm
http://www.zetatalk.com/science/s94.htm

and many others. Lightning heats the air around it at 150km/s, many, many times the speed of sound.

[Tez]

Originally posted by scotth


Since photos (light) or subatomic particle neither displace the atmoshpere as they pass though it, it could hardly be called a quibble.

If this was a stab at the effectiveness of scientific investigation or accuracy, it was a very poor one.

You would not know a muon exists except for serious scientific research.

Well, I'd be rather amazed if you knew more about muons than I do mate.

The first post simply said "an object".

Both photons and muons do "displace the atmosphere" in as much as they can collide with the atoms comprising it. In fact muon collisions are responsible for the majority of lower atmosphere ionisation - which is a crucial part of the atmosphere's dynamics. "Weather" for you.

The quibble was not meant to be a serious fundamental objection, and certainly not a "stab at the effectiveness of scientific investigation or accuracy":eek: but rather was a way of pointing out, to people a little smarter than you, that the explanations implicitly make use of an approximation - in this case the macroscopic nature of the object travelling through the gas.

In science quibbles are crucial to undserstanding the limits of our knowledge. They are not generally taken to be attacks on the validity of science itself.

[Andonyx]

Originally posted by shanek


Not according to these sources:

http://www.pbs.org/wgbh/nova/barrier/boom/choice2.html
http://www.abc.net.au/science/k2/moments/s512994.htm
http://www.zetatalk.com/science/s94.htm

and many others. Lightning heats the air around it at 150km/s, many, many times the speed of sound.

Yes, but that has zilch to do with the "speed" of lightening traveling through the atmosphere, and it has to do with the heating of the gas. The sudden expansion generates the boom, not the lightening itself.

[scotth]

Originally posted by Tez


Well, I'd be rather amazed if you knew more about muons than I do mate.

The first post simply said "an object".

Both photons and muons do "displace the atmosphere" in as much as they can collide with the atoms comprising it. In fact muon collisions are responsible for the majority of lower atmosphere ionisation - which is a crucial part of the atmosphere's dynamics. "Weather" for you.

The quibble was not meant to be a serious fundamental objection, and certainly not a "stab at the effectiveness of scientific investigation or accuracy":eek: but rather was a way of pointing out, to people a little smarter than you, that the explanations implicitly make use of an approximation - in this case the macroscopic nature of the object travelling through the gas.

In science quibbles are crucial to undserstanding the limits of our knowledge. They are not generally taken to be attacks on the validity of science itself.

It seems like that I misread you.

There are many posters here that would make a quite similar comment as if it was a huge failing of science. (Like, why are there all these exeptions and details.... why can't it be simple like Yin and Yang and thats it?).

[Tez]

Originally posted by scotth


It seems like that I misread you.

There are many posters here that would make a quite similar comment as if it was a huge failing of science. (Like, why are there all these exeptions and details.... why can't it be simple like Yin and Yang and thats it?).

No problem.

Your Yin and Yang comment just reminded me of a horrendous 6 hours I spent trapped in an airport terminal in the middle of China (foothills of the HuangShan mountains) listening to an old Korean physicist, who had also been at the conference, explain how an electron's spin was much like Yin and Yang. [You see, there's a little bit of the spin up in the spin down blah blah.] I decided to point out the analogy told us nothing about the "correctness" of Yin and Yang as a philosophy, and that I could learn just as valuable lessons form the relationship between the empty sandwich box to the blue chair next to me. After an hour of arguing, which actually became very heated, the guy got so upset he had to leave - but he couldnt! The place was only about 10mx10m. The colleague I was with and I still laugh over that whole incident whenever we meet up....

[Ladewig]

Not according to these sources:

http://www.pbs.org/wgbh/nova/barrier/boom/choice2.html
http://www.abc.net.au/science/k2/moments/s512994.htm
http://www.zetatalk.com/science/s94.htm

and many others. Lightning heats the air around it at 150km/s, many, many times the speed of sound.

Now I am really confused. These three sites each give different explanations as to the source of thunder.

PBS says the air is heated so quickly that it creates a shock wave that travels faster than the speed of sound.

ABC says it is the tip of the lightning bolt travelling at 150 km/s that creates a sonic boom.

Zetatalk says it is not the superheating of the air that generates the shock wave or noise, it is the superheated air (at a very high pressure) rushing into the low pressure area created after the lightning disappates that creates the sound.

[jj]

Originally posted by Tez


Well, I'd be rather amazed if you knew more about muons than I do mate.

The first post simply said "an object".

Both photons and muons do "displace the atmosphere" in as much as they can collide with the atoms comprising it. In fact muon collisions are responsible for the majority of lower atmosphere ionisation - which is a crucial part of the atmosphere's dynamics. "Weather" for you.

The quibble was not meant to be a serious fundamental objection, and certainly not a "stab at the effectiveness of scientific investigation or accuracy":eek: but rather was a way of pointing out, to people a little smarter than you, that the explanations implicitly make use of an approximation - in this case the macroscopic nature of the object travelling through the gas.

In science quibbles are crucial to undserstanding the limits of our knowledge. They are not generally taken to be attacks on the validity of science itself.

You know, that kind of insult really doesn't present you in a good light.

Quibbles are useful, but when everyone else is discussion macroscopic object, you could point out, with rather less rancor, that microscopic (or smaller) objects, especially those with unusual properties, might not act the same way. Now, I wonder when a muon does strike something, does it cause heating, i.e. does it cause a (small) amount of sound? If it increases the thermal motion in the atmosphere, yes, it does, strictly speaking, create sound, just not MUCH sound.

As an aside (yes, I know the answer as reported by several old Bell Labs folks who have also retired along with me), what is the level of atmospheric noise between 20Hz and 20kHz at the eardrum (area matters, of course)?

It's just like your dubvious behavior in the "Bible Code" thread. For the record, I finally read the paper on an airplane, it took me more than 15 minutes and well under 30, and the one place that I was off was that the original "experiment" was even more open-ended than I had imagined. I won't address how their distance metrics emphasized the farthest out, etc, but you've also read the paper, and perhaps David has quietly shredded a copy, too?

It made my original (be surprising if it didn't happen) estimate look pretty good. (More to the point, for one name alone, the chance was that there were a fair number of 9's in favor of it happening.)

You know a lot, but you really don't convey it very well. You tend to get peoples' back up at the start. Doesnt' serve your message well.

I spent a lot of years (22+-) up on the 5th floor in Building 2 before it got to look like it was bombed out (by the listening room) and I dare say we didn't all convey ourselves quite like that in the bad old days.

[Tez]

Originally posted by jj


You know, that kind of insult really doesn't present you in a good light.

Quibbles are useful, but when everyone else is discussion macroscopic object, you could point out, with rather less rancor, that microscopic (or smaller) objects, especially those with unusual properties, might not act the same way. Now, I wonder when a muon does strike something, does it cause heating, i.e. does it cause a (small) amount of sound? If it increases the thermal motion in the atmosphere, yes, it does, strictly speaking, create sound, just not MUCH sound.




My original post had absolutely no rancour. It simply said "photons and muons travel fine through the atmosphere at > 330m/s, and neither make sonic booms.". As a way of pointing out that I realized this was a quibble, I stated "Science is really an endless game of quibbles". And it really is - we analyze the limitations of every theory and experiment by quibbling it.

Scotth misunderstood my meaning, and replied with a rancourous post to which I responded in kind. You can take me to task for this latter post, and I agree that taken out of context it is not particulalrly friendly.

It's just like your dubvious behavior in the "Bible Code" thread. For the record, I finally read the paper on an airplane, it took me more than 15 minutes and well under 30, and the one place that I was off was that the original "experiment" was even more open-ended than I had imagined. I won't address how their distance metrics emphasized the farthest out, etc, but you've also read the paper, and perhaps David has quietly shredded a copy, too?

It made my original (be surprising if it didn't happen) estimate look pretty good. (More to the point, for one name alone, the chance was that there were a fair number of 9's in favor of it happening.)


Hard to tell from this post whether you really have understood the issues completely.

Your original claim, IIRC (and I quite possibly dont remember perfectly) was that a similar search through Moby Dick for the same list of names/dates would find them with high likelihood. (At this stage you didnt understand that the point is to find them "close" with respect to their particular measure of distance, the suitability of which is a different issue.)

Regardless - this claim is simply wrong - as anyone who had read the paper would have realised. They had repeated the search on War and Peace, and various randomized versions of the torah, and had not found thatparticular list with any significance. Noone was disputing those particular findings. Any "top of the head" estimate such as you advocated (but never performed) would have failed. (And would have been a little difficult to perform, given the necessity of accounting for the closeness of ELS's.)

What was in dispute was the selection process for the particular names/dates etc. The implication in the SS paper was that this was "unbiased" - by virtue of the supposedly a-priori criterion re length of writeup in an already published book.

In fact, as took MUCH longer than 1/2 an hour, or a day or a week to show, there was enough flexibility (in spellings, appelations etc) that if we search through Moby Dick allowing ourselves the same flexibility, we could reproduce (with a different list but one just as "acceptable" by the subjective criteria) the same level of significance.

Let me repeat: The skeptics who examined the paper contended that there was enough "wiggle room" for the data to be explained by non-supernatural means. However NONE of these skeptics advocated, as you did, that the bible codes was merely a case of these people being incapable of doing some simple mathematics.

The reaon I was annoyed by your post was simply that it does a great disservice for intelligent skeptics, as I'm prepared to admit you are, to pass comment without educating themselves. EXACTLY the same problem led to the sTARbaby affair. Notice that it was also a misunderstanding about the objectivity of the a-priori data in both cases that caused the problem - and this is something that is painful to prove, but sometimes necessary.

From http://www.wopr.com/biblecodes/TheCase.htm
Now I turn to the data in the famous Rabbis experiment and the most serious problem with the WRR paper. While there are legitimate questions about the choice of dates, the place of the most significant wiggle room, which as we’ll see can totally explain what was found, is the list of appellations that WRR used.

On its web site, Aish has put its finger on what is needed for a test to be scientifically valid [41]: "The words to be searched for must be derivable by a priori specified and repeatable methods". The list must be objective so that another researcher can replicate the choices in the list. It should not be based on subjective judgements.

Let’s see what WRR have to say about the choice of the list of appellations. Their main statement is that "The list of appellations for each personality was provided by Professor S. Z. Havlin, of the Department of Bibliography and Librarianship at Bar Ilan University, on the basis of a computer search of the Responsa database at that university". They also provide four spelling rules that they use but that is all they say about how the list was constructed.

When mathematicians began to seriously look at the details, many questions were raised – for example, it turns out that for 12 of the 32 Rabbis, Prof. Havlin didn’t use the Responsa database [42]. In response to a list of queries, Prof. Havlin provided a statement with various details about his construction of the list [43]. Prof. Havlin’s testimony makes it clear that the list is not objective. That is, two well-meaning scholars starting from scratch and working independently would arrive at very different lists. He calls a large section of his document "Professional Judgements" and says he had to use discretion in making choices. Not even in Alice in Wonderland would a list that required judgements on the part of the list maker be called objective. Indeed, since he says in several places that he can’t recall why he didn’t include certain names, it is clear that not only wouldn’t the list be the same if another scholar produced it, it wouldn’t be the same if the same scholar produced it ten years later.

Along the way, Prof. Havlin poses a large number of rules, many of which are clearly arbitrary. For example, he states that appellations must be pronounceable to be included? Why? Any Talmudic student seeing the letters beis-yud, would know that the Bais Yosef (Rabbi Yosef Caro) is intended. But Prof. Havlin says that this isn’t a legitimate appellation because it isn’t pronounceable. If HaShem placed Rabbis’ names in the written Torah, why would He fail to use the most common written nicknames for those Rabbis? The pronouncability rule is an arbitrary one that another scholar making the list might not use. In addition since the rules have only been made explicit years after the experiment was published, the lists also lack the property of being a priori.

It is critical to realize that the choice of rules in making the list is as much a part of making the list as then applying those rules. Once the list is subjective, the experiment becomes a test of the list, not of Bereishit. Rabbi Mechanic’s clear criteria, with which the scientific world would agree, that the method must be repeatable is violated. The experiment isn’t valid science.

You might wonder though if the wiggle room provided by the subjective nature of the list of appellations is enough to explain the striking results of WRR. And here the interesting paper of Bar-Natan and McKay [44] (henceforth BNMK) provides the answer. They produced another list of reasonable appellations, many of them in common with the WRR list [45].

Recall that WRR found that the WRR list had a statistical correlation with the dates when looked for in Bereishit but not in War and Peace. Similarly, BNMK found that the BNMK list had a statistical correlation with the dates when looked for in War and Peace but not when looked for in Bereishit. The correlation that BNMK found in War and Peace for their list was as statistically significant as what WRR found in Bereishit for their experiment. So BNMK show that the wiggle room in the list is indeed enough to totally explain the phenomenon observed by WRR.







Back to your post:


You know a lot, but you really don't convey it very well. You tend to get peoples' back up at the start. Doesnt' serve your message well.


Point taken. Not the first time I've heard it, and I am actually getting better, despite appearances :)

[Crossbow]

Originally posted by Soapy Sam
How big must an object be, to make a sonic "boom"?
Do very small, very fast objects (eg a squirrel, ductaped to a small rocket), make a sonic "pop"?

To: Soapy Sam

It looks like no one has really tried to answer your question, so please allow me an attempt.

Essentially, any object that travels through the atmosphere that is big enough to make a distrubance, or atmospheric wake, which is travelling faster than the speed of sound will make a sonic boom.

The magnitude of the boom is dependent upon many factors, to wit:

Atmospheric Density: cold, dry, sea level air is denser than say hot, humid, high altitude; the denser the air, the greater the boom.
Projectile Speed: the greater speed of object (once it exceeds the speed of sound) will serve to increase the magnitude of the boom.
Projectile Sound: a projectile that travels with little to no noise (such as a bullet) will make less of a boom than a projectile that has a noisy engine (such as a jet engine).
Projectile Size: a larger projectile will make a larger atmospheric disturbance, hence it will make a larger boom.

I hope this helps!

[jj]

Originally posted by Tez


Hard to tell from this post whether you really have understood the issues completely.

Your original claim, IIRC (and I quite possibly dont remember perfectly) was that a similar search through Moby Dick for the same list of names/dates would find them with high likelihood. (At this stage you didnt understand that the point is to find them "close" with respect to their particular measure of distance, the suitability of which is a different issue.)

I was, in fact, unaware of their (adjective deleted) "distance" calculation. Given the number of permutations available, you notice I'm still annoyingly unamazed.


Regardless - this claim is simply wrong - as anyone who had read the paper would have realised. They had repeated the search on War and Peace, and various randomized versions of the torah, and had not found thatparticular list with any significance. Noone was disputing those particular findings. Any "top of the head" estimate such as you advocated (but never performed) would have failed. (And would have been a little difficult to perform, given the necessity of accounting for the closeness of ELS's.)

Actually I did perform such a calculation, it came out rather more optimistically than I had expected, but I was only calculating the chance of getting different words with different strides, etc.


What was in dispute was the selection process for the particular names/dates etc. The implication in the SS paper was that this was "unbiased" - by virtue of the supposedly a-priori criterion re length of writeup in an already published book.

One thing that's in dispute, at least, I'll agree with that. The idea of arguing for a constant spelling for most anything in most any language that isn't ideographic had in fact crossed my mind, I did not, in fact, realize that they had made such extensive use of it. In other words, it was even lamer than I thought.


In fact, as took MUCH longer than 1/2 an hour, or a day or a week to show, there was enough flexibility (in spellings, appelations etc) that if we search through Moby Dick allowing ourselves the same flexibility, we could reproduce (with a different list but one just as "acceptable" by the subjective criteria) the same level of significance.

As I said "unsurprised" is how I feel about that. I'd expect that one could do the same thing with many other books. You do recall I didn't say I could FIND a list, rather figure out a decent estimate of how likely it was. I still contend I can do that, of course, that doesn't address the "distance" issue.


Let me repeat: The skeptics who examined the paper contended that there was enough "wiggle room" for the data to be explained by non-supernatural means.
To me, that is a much more serious accusation, and one I'm unwilling to make without some evidence, unlike:

However NONE of these skeptics advocated, as you did, that the bible codes was merely a case of these people being incapable of doing some simple mathematics.

That's not quite how I'd put it. I didn't think that they were incapable of doing some simple mathematics, I thought that they were creating significance by choosing their measure (rather than their data). I still think they were. The article makes a very good case for the argument that they also used flexibility in their data. I won't dispute that, but I haven't the evidence to produce to argue that on my own.


The reaon I was annoyed by your post was simply that it does a great disservice for intelligent skeptics, as I'm prepared to admit you are, to pass comment without educating themselves.
You're correct at some level, I hadn't assumed that the lameness was so thorough. :(

EXACTLY the same problem led to the sTARbaby affair. Notice that it was also a misunderstanding about the objectivity of the a-priori data in both cases that caused the problem - and this is something that is painful to prove, but sometimes necessary.

I don't know about that one, I fear.


Back to your post:

Point taken. Not the first time I've heard it, and I am actually getting better, despite appearances :)
Ok. I'll take you at your word on that one.

[Soapy Sam]

Crossbow- Thanks. So the sound of a supersonic squirrel clapping one hand is...?

I'm off to listen to Ramachandran on the radio,

[Crossbow]

Soapy Sam, I am glad you found the data useful.

Now then, I do have my own ideas as to sound made by one-hand clapping, but this is a G-rated board, so I will not furnish a detailed explanation.

Here is hint: it ryhmes with "Thanking"!

:p

[rwguinn]

Originally posted by Crossbow




The magnitude of the boom is dependent upon many factors, to wit:

Atmospheric Density: cold, dry, sea level air is denser than say hot, humid, high altitude; the denser the air, the greater the boom.
Projectile Speed: the greater speed of object (once it exceeds the speed of sound) will serve to increase the magnitude of the boom.
Projectile Sound: a projectile that travels with little to no noise (such as a bullet) will make less of a boom than a projectile that has a noisy engine (such as a jet engine).
Projectile Size: a larger projectile will make a larger atmospheric disturbance, hence it will make a larger boom.

I hope this helps!

Almost correct-Projectile sound has almost nothing to do with the shock wave. Projectile SHAPE, otoh, has a great deal to do with it.
The STS is not truly designed for supersonic flight-it is designed to slow down (atmospheric re-entry is the ultimate slow-down, so far as we can do) and land. It is also unpowered. The "sonic booms" (yes, there are 2) come from the leading and trailing edges, and are particularly nasty.
I recall the F-104 and the SR-71 at supersonic speeds-the 104 has very sharp double boom, and SR71 has a very loooonnng drawn-out thing, much more like a bass measure in music..