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Sonic Boom, Red Bull Stratos (possible?)

  1. Oct 29, 2012 #1
    Hello, first topic in this forum, if this is not the correct sub-forum, I apologize in advance.

    Well the question is:

    Is it possible for Felix Baumgatner, to produce an audible sound from earth sonic boom?.

    Red bull has released what suppose to be that a micro sonic boom from the guy breaking speed barrier.


    http://www.youtube.com/watch?feature=player_embedded&v=yZFz6y4UCuo

    The thing is that from what i've research it won't be no possible due that:

    1) You can not make a sonic boom if you make no sound.
    2) The sonic cone that is formed, the wave is not pouting to ground (unlike the jet wave), because he was facing ground.
    3) Even if possible it should be so small that it would be no audible from ground.

    Well, sorry if it something obvious or the question is not proper formatted according to the forum rules.

    Thanks in advance.
     
  2. jcsd
  3. Oct 29, 2012 #2

    mfb

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    Humans make sounds simply by moving very fast through the air.

    It is a cone, moving down- and sidewards.

    Any numbers to show that?
     
  4. Oct 29, 2012 #3

    Hi, thanks for your answer, I just miss a some question marks, specially the 3) question :-).

    So the 3 rd was a question.

    The second one, ok, but the waves aren't moving paralel to ground? Should they be in that case audible from ground?,

    And the most important, do you think by your knowledge that in fact what we are hearing in that video is a human body in free fall breaking the sound barrier?

    Thanks.
     
  5. Oct 29, 2012 #4

    mfb

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    If they would move parallel to the ground only, you could not hear it on the ground - the supersonic fall was in a height of ~25km.

    I don't know. Maybe. Someone would have to calculate it.
     
  6. Oct 29, 2012 #5

    AlephZero

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    Whether or not you could hear it on the ground, it doesn't make any sense that Baumgartner could hear his own sonic boom. For example passengers travelling in Concorde didn't hear a boom, because it was left behind them.

    It's possible Baumgartner's microphone picked up some aerodynamic buffeting as the airflow around him changed from subsonic to supersonic, and that sounded like a couple of bumps, but that wouldn't actually be the "boom".
     
  7. Oct 29, 2012 #6

    But Baumgartner, didn't fell anything at all (say it by himself).

    The video I just linked, was filmed (and audio recorded) from ground "pointing" to Baumgartner in the sky while fallling.
     
  8. Oct 29, 2012 #7

    AlephZero

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    I didn't realize that. The video has obviously been edited, and the first part was (I assumed) sound from Baumgartner's microphone.

    A good check would be the time after the start of the jump when the alleged boom was heard, but the edited video doesn't give that information. The time for the sound to reach the ground level would be of the order of a few minutes (the exact time is messy to calculate because the speed of sound depends on altitude, but it wuuld worth doing if there was something to check it against).

    It could have been a boom from a supersonic aircraft observing the jump, not from Baumgartner.
     
    Last edited: Oct 29, 2012
  9. Oct 30, 2012 #8

    boneh3ad

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    There is always going to be some degree of sonic boom coming from a supersonic object. How pronounced it is and who can hear it is a different story. The main issue I see here is that he was falling nearly straight down for the free-fall portion of the jump, so the shock waves would not touch the ground, and if they don't touch the ground, no one on the ground can hear a sonic boom.

    The sound heard is a double boom, which is pretty characteristic of low-flying supersonic aircraft. I am not so convinced that a falling person would be of sufficient mass and the right shape to create a double boom. My money is on it either being a doctored video or some nearby supersonic aircraft, which are fairly common in that area of the country.
     
  10. Feb 16, 2013 #9
    I think that's correct. He was supersonic, which means there certainly was a pressure shock wave in the front and a negative pressure wave from behind, but was he going straight down, feet first or head first? If so, you'd think that pressure wave would be very small.

    If he was falling "flat" like skydivers do when making fancy maneuvers, the pressure wave would be bigger, but the negative pressure wave would not be far behind so the two "booms" would have to be so close together that they would sound like one. Plus it probably would hurt like hell. Imagine if he fell through a hailstorm. LOL

    Just guessing, but I assume he fell in a manner that would reduce the pain as much as possible, so that would suggest the minimum possible pressure wave, but at some point he would have had to reduce his speed, otherwise the deceleration upon opening the chutes would probably be too much to survive.

    I also wonder about the rapid change in temperature that he must have endured, starting out at extremely low temperatures, then rapidly rising temperatures due to friction. At 800+ MPH that friction must have been intense. The more I think about it, this stunt was a really amazing accomplishment. Beats a barrel over Niagara Falls any day. LOL

    Since that meteor hit Russia, I've seen a lot of misinformation about sonic booms out there, the most common ones seems to be:

    "The sonic boom is generated by passing though the sound barrier."
    True, but misleading, you get a sonic boom after you pass the sound barrier, too.

    "Sonic booms are caused by the so called "Mach Cone.""
    Wrong, for example if a supersonic bullet passes close by your head you don't hear the sonic boom "crack" - it sounds more like a buzzing noise, because the "Mach Cone" is going by your head. When I was in Nam, if you heard that buzzing noise you ducked real quick because you almost bought it and you probably needed to clean your underwear as well LOL.

    If you heard a "crack" that meant the bullet (and the "Mach Cone") missed you by a lot. The "Mach Cone" is a nice geometrical model to help explain sonic booms to laypersons, but that's about it, IMO.

    "Only objects traveling at supersonic speeds generate sonic booms or you need a "shock wave" to generate a sonic boom."
    Nope, here's an example, place 100 omnidirectional speakers exactly the same distance from a particular spot. A circle of speakers with a diameter of 1 km would work nicely. Send a pulse of white noise to each speaker at the same time. If you're standing in the middle of that circle, you hear a sonic boom. Anywhere else and you don't. Stonehenge has an effect something like that with properly positioned and timed drummers.

    Excellent website with video examples showing why sonic booms occur.
    http://www.acs.psu.edu/drussell/Demo...r/doppler.html [Broken]

    When I show this to someone not especially science literate, I skip all the math and tell them to visualize (soundulize? LOL) that each expanding circle represents a single ring of a bell. In other words, pretend there is a person ringing a bell on the airplane at a steady rate.

    Then place your finger on the video anywhere you want and say "ding" every time a circle hits your finger.

    In the first example you hear the bell, ding, ding, ding, ding, no matter where you put your finger (except right on the dot, of course) just like you would expect and just what it would sound like on the plane.

    In the second, if your finger is directly above or below the dot and to the right, the dings come closer together than in the first example (forget mentioning the frequency change or you'll lose them). If you put your finger to the left, the dings are farther apart than the first example.

    Then I tell the person to imagine the airplane going faster and faster - the dings will come closer and closer together, until you get to the point where it no longer sounds like single dings, but rather a continuous noise.

    Then I move on to the third picture and repeat - put your finger above or below just to the right of the dot and count the dings - you get a bunch of them all at the same time, after which you hear dings again. Voila! that's a sonic boom - lots of dings all added together to make one loud ding.

    The fourth example explains the bullet past the head phenomenon. Place your finger very slightly above or below and to the right of the airplane and you can see that the "Mach Cone" passes by, NOT the added together dings. Place your finger lower or higher and to the right and you then get the sound summation.

    Then I explain the double sonic boom by pointing out that the video only shows sound coming from the back of the airplane, when in reality sound is generated simultaneously from the front shock wave AND the rear shock wave and there is a considerable distance between the two sources of sound (The bell ringing analogy no longer works very well) so you have two summed sounds a fraction of a second apart instead of just one.

    "The sonic boom comes only from the shock waves"
    No, the boom comes from ALL the noise coming from the plane with jet engine noise being the most important besides the shock wave noise. ALL of it contributes to the sonic boom intensity. In fact, if the pilot wants to make a really loud sonic boom, he turns on the afterburners.
     
    Last edited by a moderator: May 6, 2017
  11. Feb 16, 2013 #10
    It's nowhere near this simple, which is one reason I dislike the "Mach Cone" explanation.

    If the guy was falling straight down and there was no wind, then the sonic boom would be moving straight down and wouldn't be especially cone-shaped. There would only be sideways movement if the faller had significant tangential velocity NOT caused by a cross-wind.

    That's extremely unlikely though, since at that altitude there must have been very strong wind currents not necessarily consistent in speed and direction with height. Another complication would be passing through thermal layers which would refract the sound.

    In real life situations, it is not an easy task to predict when and where a sonic boom from a falling person will hit the ground and you cannot predict it accurately by using a simple cone model.
     
  12. Feb 17, 2013 #11

    mfb

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    I think this is just a question of definition - if you move a "/" line downwards or sidewards does not make a difference in terms of the position of the new line, if you neglect the ends.
    On the other hand, you can hear the boom if you are not in the direct line of the aircraft/person, so energy has to move sidewards to reach you.

    Wind on earth is usually slow compared to the speed of sound. Some deflection/reflection in the air is possible, of course.
     
  13. Feb 17, 2013 #12
    All true, however sound always propagates in a spherical pattern, regardless of the speed of the source, (but relative to the velocity and direction of the air media it travels through). If the frame of reference of the observer is not too different from the media and the source is far away, the radius of curvature will be large enough that it is pretty close to a plane wave when the boom hits the ground. (Nice name for a rock song, "when the boom hits the ground" LOL). I'm assuming the source is falling straight down with respect to the observer(s) of course.

    Caveats: The intensity can vary considerably around that propagating sphere (like when using a megaphone), of course, and it's debatable whether supersonic shock waves can really be called "sound," (shock waves caused by non-directed high explosives are certainly not "sound" although they do often propagate spherically) Shock waves from supersonic sources (which do not propagate spherically) slow down to the speed of sound rapidly, then become normal sound waves, making the "Mach Cone" a very useful illustrative device. (see the cool link in my post above)

    But I think you are referring to the location of the major constructive interference node(s) with time. I don't call that the "Mach Cone," but others do, which is confusing. That node can indeed appear to move sideways in time depending on the way the propagating waves interfere with each other, even if the source is falling straight down, however I think it is likely that a person directly below the falling person and someone say 500 feet away would probably hear the boom at essentially the same time under most conditions. A mile away and that's a different story.

    I'm not suggesting that wind causes a lot of deflection/reflection/refraction - rather that it can complicate the interference pattern considerably, weakening and altering the position of the major constructive interference node that is the sonic boom(s), although keep in mind that high altitude winds can sometimes reach nearly 200 mph.

    I'm just nit picking, actually. I was a sonar tech in the US Navy, am a musician, and a PhD physicist/chemist, so I love speculating on anything related to sound. I'm not saying I have all the answers - anything incorrect with my logic and I'd appreciate someone correcting me.

    On a lighter note, if a sonic boom is generated above a forest, knocking down trees, but with no ears there to hear it, does it make a sound? LOL
     
  14. Feb 18, 2013 #13
    Zentrails, I don't mean to hijack the thread but I think this is somewhat related, and you seem knowledgeable.

    ...the meteor in Russia, I keep hearing people saying that the sonic boom caused all the damage. I'm not coninved that's true (since the thing supposedly exploded with 500kt TNT), but what do you think? Did the sonic boom or the explosion cause the damage? If not the sonic boom, COULD a sonic boom from a meteor casue that much damage? How big or how fast would it have to be?
     
  15. Feb 18, 2013 #14
    Doubt it, just look at the Tunguska Event Wiki page:

    https://en.wikipedia.org/wiki/Tunguska_event

    The estimate is that the explosion might have been as little as 3 Megatons.
    quoting Wiki: "the zone of leveled forest occupied an area of some 2,150 square kilometres (830 sq mi)"

    I think a 0.5 Megaton blast would have done far more damage than we saw in Russia the other day (maybe I read that wrong?). And since it was clearly closer to the ground than the Tunguska, it would have made a smaller but much deeper crater, IMO.

    I don't think you can knock over a tree with a sonic boom, although there must have been one (two?) and you'd think it would be much more powerful than anything the Red Bull Stratos guy would have made. LOL

    i.e. I think the reports of a sonic boom causing most of the damage was wrong as well as the 0.5 Megaton estimate. Makes for a more entertaining TV news report, though.

    If they find a meteorite associated with that event, then maybe it was only a sonic boom, and they can certainly break windows, but I think the impact shock wave would have been far more powerful, like an earthquake.

    I saw a pic of an iced over lake with a nearly perfectly round hole in it, that some were claiming was caused by the meteor. Seems unlikely that you'd get a nice round hole with no fractures radiating out from it, though, seems doubtful that was meteor caused.

    They looked for decades for the Tunguska meteorite and couldn't find anything - which suggests that the air blast alone was powerful enough to register as a Richter 5 earthquake.

    It would be interesting if someone analyzes the audio from Russia to see if a much quieter sonic boom occurred before or after that large bang sound. It would probably be after the blast if it were an air-burst, but probably before the blast if the object landed somewhere (although the speed of sound is faster through solids and shock waves can travel much faster than sound in any media, so who knows? I guess it would depend on where you were standing.)

    At any rate, even without doing any calculations, it seems intuitive that either an air-burst OR an impact would create a huge shock wave much more powerful than the sonic boom(s) associated with the object.

    Another thing to consider is that sonic booms contain a limited band of audio frequencies, usually at the higher end, whereas an explosion shock wave also causes low frequency sound that would probably be a lot more destructive as any rock concert veteran knows. LOL

    One thing for sure, as the meteor entered the atmosphere, as soon as it reached a reasonable air density at supersonic speeds, the pressure on the leading edge of the meteor must have been high causing very high temperatures to build up on that leading edge very quickly (there's actually no such thing as "friction"). So, the exact same phenomena that supersonic planes experience (and pilots say they can feel) is what causes meteors to explode mid-air.

    For example, supersonic jet engines have special input baffle type devices to slow the incoming air to subsonic speeds, otherwise the turbine blades would quickly disintegrate due to the high, turbulent (non-laminar) pressure.

    Comets must be the worst, since they contain so much water. The ancients had good reason to consider comets bad omens!

    Is there a thread on air-burst shock waves? If so, we should move this there.
     
    Last edited: Feb 18, 2013
  16. Feb 18, 2013 #15

    cjl

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    What makes you think it was closer to the ground? It was incredibly high up in the air - estimates I've seen put it at an altitude of 15-25 km at the time of the disintegration, while the estimates for Tunguska put it at 5-10km. A 500 kiloton blast at 15-25 km would probably not do all that much damage, since the energy would be spread out over a huge area.

    Sure you can knock over a tree with a sonic boom. Sonic boom strength depends on a number of factors, including the size of the object, the geometry of the object, and the speed at which it is traveling. Of course a house-sized blunt object traveling at mach 30 will make a stronger boom than a person going mach 1.1. There's no difference (physically) between a sonic boom and a shock wave, aside from the fact that usually, a sonic boom has dissipated enough by ground level to have an extremely small overpressure. A very large boom, or one generated at low altitude will behave exactly like a shock wave from an explosion.

    What impact shock wave? It disintegrated in midair, and the pieces were traveling fairly slowly by the time they impacted.

    I have no idea what dropping a dump truck sized boulder through several feet of ice at high speed would do, and I suspect this is one of those areas where common sense could be misleading.

    A sonic boom is basically an N-shaped pressure wave, which contains a broad range of frequencies (including very low frequencies). I suspect the majority of the energy of the meteor did go into a sonic boom, and when it broke apart, that would greatly increase the cross sectional area, and thus greatly increase the sonic boom strength.

    Yes, the heating is due to compression, though this is a bit oversimplified. Also, jet engines use their inlets not because the turbine blades would disintegrate, but rather because the turbine blades are not designed to efficiently compress and recover pressure from supersonic air. The losses would be enormous. The inlets are designed to slow the air down because this increases the efficiency of the engine, as well as because this slowing down provides the first stage of compression of the air (and jet engines want to compress the air as much as possible).

    I suspect that they would be prone to breaking apart very high in the atmosphere, which would be less of a hazard than something which penetrates far down towards the ground intact. That's just a guess though.
     
  17. Feb 18, 2013 #16
    Wow, where to begin. You contradict your own arguments repeatedly.

    Here's a link to the "meteor lake"
    http://news.yahoo.com/russia-asks-stop-space-objects-hitting-earth-213327578.html [Broken]

    That really look like a crater to you? What happened to the recoil? What happened when the object bounced off the bottom? Why is it round since the object certainly had considerable tangential velocity?

    A shock wave and a sonic boom are clearly two different things. The first is mostly a single moving pressure front, the second is a constructive interference phenomenon. A supersonic object does create a shock wave but it turns rapidly into a sound wave.

    "What impact shock wave?" the one that would occur if the meteor did NOT explode in mid-air. If there were a lot of pieces of debris, you'd think someone would have found one by now, since meteorites are especially easy to find on snow or ice, so that argument hits the dust, literally. LOL
     
    Last edited by a moderator: May 6, 2017
  18. Feb 18, 2013 #17
    "MOSCOW (AP) — With a blinding flash and a booming shock wave, a meteor blazed across the western Siberian sky Friday and exploded with the force of 20 atomic bombs, injuring more than 1,000 people as it blasted out windows and spread panic in a city of 1 million.

    While NASA estimated the meteor was only about the size of a bus and weighed an estimated 7,000 tons, the fireball it produced was dramatic. Video shot by startled residents of the city of Chelyabinsk showed its streaming contrails as it arced toward the horizon just after sunrise, looking like something from a world-ending science-fiction movie."

    This is apparently where the "400 kt" figure came assuming they meant an "atomic bomb" about the size of the Trinity test.

    I love the part where NASA supposedly says the "the meteor was ONLY about the size of a bus and weighed an estimated 7,000 tons" emphasis added.

    Oh, and there is no such thing as an "N-wave."
     
  19. Feb 18, 2013 #18
    So, which is it, people?

    Did a 7,000 ton object create a sonic boom that caused all the damage, then apparently land somewhere without making even a whimper?

    OR was there a gigantic mid-air explosion that caused a huge shock wave with maybe a little sonic boom added to it? You do the math.

    You have to be careful what you believe reading news reports.
     
  20. Feb 18, 2013 #19
    Wiki:

    "The strongest sonic boom ever recorded was 7,000 Pa (144 psf) and it did not cause injury to the researchers who were exposed to it."

    Course the author of that article thinks U and N waves exist.

    I did get the frequency band width backwards: "The energy range of sonic boom is concentrated in the 0.1–100 hertz frequency range" It's mostly low frequency not high.

    https://en.wikipedia.org/wiki/Sonic_boom

    It's certainly true that supersonic engines run more efficiently when fed subsonic air, so what?
    You can't get less efficient than a turbine engine that self-disintegrates.
    That's also why helicopters are limited in how fast they can go - they have to make sure the tips of the blades do not exceed the speed of sound or they start vibrating like hell.
    Same thing with turbines.

    Should I continue with the debunking?
     
    Last edited: Feb 18, 2013
  21. Feb 18, 2013 #20

    cjl

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    Sure there is. It's nothing special - an N-wave is simply a wave where the pressure vs time graph as it passes a given location is in the shape of a capital letter N (a very sharp pressure rise, followed by a linear pressure drop to below ambient, followed by another sharp rise back to ambient at the end of the boom). See this page for more details:

    http://www.mcgill.ca/mecheng/staff/sivanadarajah/research [Broken]
     
    Last edited by a moderator: May 6, 2017
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