NickDG 23 #1 February 21, 2010 Never saw anything like this before . . . (Which is good because sometimes I think I've seen it all.) http://www.youtube.com/watch?v=SsDEfu8s1Lw&feature=player_embedded# NickD Quote Share this post Link to post Share on other sites quade 4 #2 February 21, 2010 NASA's view of the same launch. http://www.youtube.com/watch#playnext=1&playnext_from=TL&videos=UegP-TebcdE&v=rQTqCgf7x_Y Doesn't show the same effect. My guess is there's something goofy going on.quade - The World's Most Boring Skydiver Quote Share this post Link to post Share on other sites NickDG 23 #3 February 21, 2010 Damn, if it's fake, I have seen it all . . . NickD Quote Share this post Link to post Share on other sites wolfriverjoe 1,523 #4 February 21, 2010 QuoteNASA's view of the same launch. http://www.youtube.com/watch#playnext=1&playnext_from=TL&videos=UegP-TebcdE&v=rQTqCgf7x_Y Doesn't show the same effect. My guess is there's something goofy going on. Not necessarily "goofy". The title of the video Nick linked includes "sundog". That video had a different angle than NASA's. I think it's a combination of the sun and the shockwave creating an odd reflection. If you look at the other videos in Nick's link, there are lots them that have a visual (usually moisture condensing in the shockwave) of going supersonic. If you get a good angle and the right shockwave you can get some goofy reflections/refractions."There are NO situations which do not call for a French Maid outfit." Lucky McSwervy "~ya don't GET old by being weak & stupid!" - Airtwardo Quote Share this post Link to post Share on other sites ZigZagMarquis 9 #5 February 21, 2010 Thanks Nick for making science FUN! If anyone wants to read more about the "why" in this, go check out: http://mysite.verizon.net/lbalders/f18_sb.htm http://www.wilk4.com/misc/soundbreak.htm http://www.answers.com/topic/sonic-boom Quote Share this post Link to post Share on other sites Niki1 1 #6 February 21, 2010 Not necessarily "goofy". The title of the video Nick linked includes "sundog". That video had a different angle than NASA's. I think it's a combination of the sun and the shockwave creating an odd reflection. If you look at the other videos in Nick's link, there are lots them that have a visual (usually moisture condensing in the shockwave) of going supersonic. If you get a good angle and the right shockwave you can get some goofy reflections/refractions. I was standing on the causeway at NASA for the first shuttle launch in 1980 ('81?). We were 6 1/2 miles away from the pad and as the sound came across the water, it rippled as it went like a big school of fish comming our way. When it got to us, you could feel it. It didn't sound that loud, like a rock concert speaker or even a jack hammer but like you were in a bass drum with a thousand drummers beating on it. The JVC advertisement withe the guy seating in the "sonic wind" was what it felt like. That launch is one of the most awesome things I've ever witnessed.Most of the things worth doing in the world had been declared impossilbe before they were done. Louis D Brandeis Where are we going and why are we in this basket? Quote Share this post Link to post Share on other sites
quade 4 #2 February 21, 2010 NASA's view of the same launch. http://www.youtube.com/watch#playnext=1&playnext_from=TL&videos=UegP-TebcdE&v=rQTqCgf7x_Y Doesn't show the same effect. My guess is there's something goofy going on.quade - The World's Most Boring Skydiver Quote Share this post Link to post Share on other sites
NickDG 23 #3 February 21, 2010 Damn, if it's fake, I have seen it all . . . NickD Quote Share this post Link to post Share on other sites
wolfriverjoe 1,523 #4 February 21, 2010 QuoteNASA's view of the same launch. http://www.youtube.com/watch#playnext=1&playnext_from=TL&videos=UegP-TebcdE&v=rQTqCgf7x_Y Doesn't show the same effect. My guess is there's something goofy going on. Not necessarily "goofy". The title of the video Nick linked includes "sundog". That video had a different angle than NASA's. I think it's a combination of the sun and the shockwave creating an odd reflection. If you look at the other videos in Nick's link, there are lots them that have a visual (usually moisture condensing in the shockwave) of going supersonic. If you get a good angle and the right shockwave you can get some goofy reflections/refractions."There are NO situations which do not call for a French Maid outfit." Lucky McSwervy "~ya don't GET old by being weak & stupid!" - Airtwardo Quote Share this post Link to post Share on other sites
ZigZagMarquis 9 #5 February 21, 2010 Thanks Nick for making science FUN! If anyone wants to read more about the "why" in this, go check out: http://mysite.verizon.net/lbalders/f18_sb.htm http://www.wilk4.com/misc/soundbreak.htm http://www.answers.com/topic/sonic-boom Quote Share this post Link to post Share on other sites
Niki1 1 #6 February 21, 2010 Not necessarily "goofy". The title of the video Nick linked includes "sundog". That video had a different angle than NASA's. I think it's a combination of the sun and the shockwave creating an odd reflection. If you look at the other videos in Nick's link, there are lots them that have a visual (usually moisture condensing in the shockwave) of going supersonic. If you get a good angle and the right shockwave you can get some goofy reflections/refractions. I was standing on the causeway at NASA for the first shuttle launch in 1980 ('81?). We were 6 1/2 miles away from the pad and as the sound came across the water, it rippled as it went like a big school of fish comming our way. When it got to us, you could feel it. It didn't sound that loud, like a rock concert speaker or even a jack hammer but like you were in a bass drum with a thousand drummers beating on it. The JVC advertisement withe the guy seating in the "sonic wind" was what it felt like. That launch is one of the most awesome things I've ever witnessed.Most of the things worth doing in the world had been declared impossilbe before they were done. Louis D Brandeis Where are we going and why are we in this basket? Quote Share this post Link to post Share on other sites
warpedskydiver 0 #7 February 21, 2010 http://www.youtube.com/watch?v=pYlJNWdt0uE&feature=related Quote Share this post Link to post Share on other sites
Calvin19 0 #8 February 21, 2010 The phenomenon shown here is not normally visual, but what we are seeing is a wave with extreme differences in pressure on the "top" and "bottom". most commonly seen in the Prandtl–Glauert singularity. super fast changes in air pressure instantaneously condense water in the air, and just as fast re-vaporize it. I was able to see it once in real life, on a civilian airplane. pretty cool stuff. one of few truly MAGIC things on earth. http://en.wikipedia.org/wiki/Prandtl–Glauert_singularity -SPACE- Quote Share this post Link to post Share on other sites
Calvin19 0 #9 February 21, 2010 Quotehttp://www.youtube.com/watch?v=pYlJNWdt0uE&feature=related far less believable than what was posted in the title post of this thread. This phenomenon IS possible. the very same thing can be seen in nuclear weapons atmospheric tests. http://www.youtube.com/user/SineCalvin9#p/f/265/k-d9iwBSswY in the first minute you can see the same effect, only happening in on barometric layer. same thing. shock waves can come from bombs (impacts) or wakes (vessels/aircraft/ships) -SPACE- Quote Share this post Link to post Share on other sites
NickDG 23 #10 February 21, 2010 That's exactly what came to mind when I first watched it, there's that pesky old Prandtl–Glauert singularity. What warped posted is a just a video or film low resolution transfer anomaly. NickD Quote Share this post Link to post Share on other sites
warpedskydiver 0 #11 February 21, 2010 Actually I just though it was cool... However it did show a similar principle with water as a medium. Salt water being far more dense than air will exhibit a similar pressure wave at a far slower speed. Quote Share this post Link to post Share on other sites
Calvin19 0 #12 February 21, 2010 Quote Salt water being far more dense than air will exhibit a similar pressure wave at a far slower speed. usually as density increases, inertial energy transfer (sound) speed is increased. Surface waves are VERY different from sound waves, if that is what you were talking about. -SPACE- Quote Share this post Link to post Share on other sites
warpedskydiver 0 #13 February 21, 2010 I was speaking to the visualization of the pressure wave. " The state properties of water (temperature and pressure) and the degree of salinity also affect the speed of sound. The propagation of sound waves in sea water can be directly affected by suspensions of particulate matter that can scatter, absorb, or reflect the waves. Laboratory experiments demonstrate that distilled water—water from which salts and other suspended particles have been removed—provides a medium in which the speed of sound exceeds the speed of sound in ocean water. The difference in the speed of transmission is significant—speed in distilled water may be 20 to 30 times that of speeds found in ocean water. Because frequency and wavelength are inversely proportional characteristics of sound waves, low-frequency signals produce long sound wavelengths. These long-wavelength signals encounter fewer suspended particles as they pass through the medium and thus are not as subject to scattering, absorption, or reflection. As a result, low-frequency signals are able to travel farther without significant loss of signal strength. Naval communication systems utilize low-frequency, long-wavelength signals to enhance communications with submerged submarines. Physical Differences Produce a "Sound Channel" Within the ocean, the speed of sound varies with changes in depth that accompany normal changes in temperature and pressure. Specific combinations of temperature, pressure, and salinity may act to create shadow zones, or reflective layers, that are resistant to the propagation of sound waves. A specific set of conditions, however, also act to create a channel through which sound waves propagate at minimal speed but with minimal loss of strength. Similar to the transmission of light through fiber-optic cables, the refraction (bending) of sound waves by layers of water with varying temperature, pressure, and/or salinity allow the formation of a well-defined sound channel. Although the oceans are not uniform bodies of water—there are currents of water with dramatic variations of temperature (such as the Gulf Stream) and salinity—the speed of sound in the deeper regions of the oceans is influenced more by high pressure. Conversely, at shallower depths, temperature plays the most dominant role in governing the speed of sound. The greater the temperature of the water, the faster sound travels. Surface temperature variation can be significant with seasonal variations in the amount of sunlight (insolation) that can produce changes in near-surface temperatures that, in turn, affect the speed of sound in water near the ocean surface. When the near-surface layer is well mixed by currents and surface action, a resulting isothermal layer allows uniform propagation speeds for sound waves. Such isothermal layers are common in mid-latitude regions. The SOFAR Channel A temperature gradient exists when the temperature of the water decreases with increasing depth. The resulting thermocline shows a characteristic decrease in the speed of sound with decreasing temperature. However, at a depth of approximately 750 meters (2,460 feet), the variations in temperature become so slight that the water becomes essentially isothermal (of uniform temperature). From that point, the speed of sound is regulated more by changes in pressure that accompany the increasing depth. Because sound wave transmission speed is directly proportional to pressure, the speed of sound increases as the pressure increases with depth. Accordingly, at the interface of the thermocline and the isothermal depths, there exists a region of minimal speed of sound. This interface creates a sound "pipeline," or "deep sound channel," within the oceans that allows the transmission of low-frequency sound over thousands of kilometers. This sound fixing and ranging (SOFAR) channel was discovered in 1943 by an American team led by Maurice Ewing and J. L. Worzel, and independently by Soviet physicist Leonid Brekhovskikh. Ewing and Worzel demonstrated that the SOFAR channel was capable of transmitting the low-frequency, long-wavelength sound waves produced by an explosion near the Bahama Islands to receivers stationed near the coast of Africa. SOFAR channel depths also are a function of the depth and thickness (extent) of the thermocline. For example, SOFAR channels run nearer the surface in colder, polar seas. Temperature and pressure affect water density, and the refraction of sound waves occurs at the interface of mediums (or layers within a medium) of differing density. Because of refraction, sound waves traveling through the SOFAR channel are deflected toward a region of lower velocity. Accordingly, waves traveling upward toward the surface, where the speed of sound increases with increasing temperature, deflect downward. Waves traveling toward deeper water, where the speed of sound increases with increasing pressure, are deflected upward. Sound waves can be trapped effectively in the narrow SOFAR channel. Traveling at minimum velocity, the sound waves lose little energy, allowing the waves to propagate over distances in excess of 25,000 kilometers (15,500 miles). Prior to the widespread use of GPS (global positioning system) equipment, the SOFAR channel also was used for navigation and the location of marine craft. Some scientists hypothesize that certain species of whales utilize the SOFAR channel to communicate mating calls over long distances. Based on the known relationship of temperature changes to changes in the speed of sound, the Acoustic Thermometry of Ocean Climate (ATOC) project is attempting to provide data crucial to measurement of changes in global temperature. By measuring differences in the speed of sound transmitted over long distances (such as across the Pacific basin), data accumulated over a long timeframe should average out variations in temperature and salinity, enabling ATOC scientists to calculate changes in ocean temperature that may provide evidence related to questions regarding global warming." K. Lee Lerner Bibliography Baggeroer, A., and W. H. Munk. "The Heard Island Feasibility Test." Physics Today 45 (1992):30. Munk, Walter, Peter Worcester, and Carl Wunsch. Ocean Acoustic Tomography. Cambridge, U.K.: Cambridge University Press, 1995. Rossby, T., and D. C. Webb. "Observing Abyssal Motions by Tracking SwallowFloats in the SOFAR Channel." JMR 17 (1970):365. Scripps Institution of Oceanography. Explorations 5, no. 2 (fall 1998). Read more: Sound Transmission in the Ocean - sea, depth, oceans, temperature, salt, system, wave, marine, salinity, Pacific http://www.waterencyclopedia.com/Re-St/Sound-Transmission-in-the-Ocean.html#ixzz0gCKaaABX Quote Share this post Link to post Share on other sites
warpedskydiver 0 #14 February 21, 2010 Agreed, but was referring to pressure not sound. Quote Share this post Link to post Share on other sites
pchapman 279 #15 February 21, 2010 QuoteI was able to see it once in real life, on a civilian airplane. pretty cool stuff. one of few truly MAGIC things on earth. It is rare to actually get to see pressure & temperature related condensation from a Mach cone, but (as Calvin19 would know) it is more common to see it from other pressure changes above a wing -- Like the fog over an airliner's wing on takeoff on a misty day, or condensation streamers coming off the wingtips of an aerobatic or fighter plane pulling G's at an airshow especially in humid conditions. Less spectacular, but even cooler because of its rarity, is to see the shock wave over an airliner's wing while flying in it. While the plane isn't supersonic, there can be regions over the wing where the local flow is hitting supersonic and creating a shock perpendicular to the wing. One time, because I happened to be sitting right over the wing next to the shock, and had the sun nicely aligned above the opposite wing, I could "see" the shock wave. The first way was from the shadow it cast on the wing, which would be a shadowgraph (see my photo), although technically not actually a Schlieren photo. The other way was that one could see the mirage-like distortion in one's vision, while looking along a certain vertical plane, affecting one's view of the wingtip. That unfortunately was just outside the photo I took. The shock wave creates sharp density changes over a short distance, which affect the refraction index of air, which creates mirages and throws shadows. Aerodynamicists dream of being able to visualize airflow, and here was a way of doing it! Still, for most people a couple faint light and dark lines on a photo aren't much to get excited about. Quote Share this post Link to post Share on other sites
Calvin19 0 #16 February 21, 2010 QuoteAgreed, but was referring to pressure not sound. word. good excerpt. on a different/same note, surface waves can give a very good model of sound waves viewed on a plane (the visualization in the launch vid in the first post of this thread essentially gave us a visualization of a pressure level in the atmosphere where the dewpoint and temperature were closer together than those above or below it. freaking AWESOME! Quote Share this post Link to post Share on other sites
Calvin19 0 #17 February 21, 2010 YYYEEEAAAHHH!!! when I saw it I was solo in a PA-30 twin comanche, at full moon in Boulder, Co. I was doing strafing runs over the runway at VNE (220mph) air was cool, humid, and dead calm. My friend Alex [i love you and miss you buddy] was watching at the end of the runway. on one of the runs, at VNE, less than 500' from alex about 10' off the ground, I gave sharp up elevator input and gave her two or three G's. The red strobe mounted on the tail gave two full flashes of the densest fog I had ever seen, only out the side windows, on top of the wing. it was not super sharp like the mach cones in the pictures, and I could tell it was patchy, but still the coolest thing I had ever seen other than flying around Alaska. After I landed Alex told me It happened on every pass but the last one was the biggest. he also said it was strongest in the wake behind the wingtips. Quote Share this post Link to post Share on other sites
Calvin19 0 #18 February 21, 2010 EVEN COOLER is the mach cones on invisible flame rocket engines. I am not a rocket surgeon, but I love that stuff. DID YOU KNOW, that even though most people think of the exhaust/air below a rocket motor is at very high pressure, it is not. in fact, on the space shuttle, below the main engines, the pressure is much lower than that of the surrounding air, these are inertial engines, not displacement engines (non-breathing) and even though a rocket has a small amount of thrust gain with atmospheric pressure, nearly all of it's thrust is from "throwing" it's inertial fuel, creating an opposite inertial reaction. (#3!!!) (at about 35-50 seconds) http://www.youtube.com/watch?v=wCY8ozgC0Kc pic http://commons.wikimedia.org/wiki/File:In-flight_close_up_of_Space_Shuttle_Atlantis_during_launch_(STS-117).jpg -SPACE- Quote Share this post Link to post Share on other sites
pchapman 279 #19 February 22, 2010 Cool stuff indeed. While we're getting away from Nick's original phenomenon, a couple nice shock diamond pics and explanation of what Calvin19 is talking about are in: http://www.aerospaceweb.org/question/propulsion/q0224.shtml Here's a couple nice shock diamond pics from a ground run of an SR-71 engine: http://www.enginehistory.org/P&W/p&w_j58.htm Rockets in space? Impossible! There's no air for them to push on! (Another visualization: I've done tuft testing on an airplane. It's fun to watch the little strings start facing the wrong way when the air separates over parts of the wing starting to stall. e.g.http://2562604189392441276-a-1802744773732722657-s-sites.googlegroups.com/site/601cgzdc/Home/Tuft-testing--vortex-generators/smCIMG4569%20%2040%20or%20just%20under.jpg?attachauth=ANoY7cq0UdOZqRMnha2ToEXrtckZi6kdEn3Zl1YOiZJ735zz7zkgjVTeeyoMPV4Ngn3s9vKFDtzNyCLPu08LOTMoMpxrOvywiDf2UlFqhWb6WBWHenqkaR-oi6ABQEfylK5bRYRWr8jdhdg3cf5B-_JcwCFCqv60y9y9mL3WGjYzRhRBGZqd6ojvVx7L6hfo8yn5GGebQqW_MTNFv4-yQv5_WZemibgdLwsw5639_cmfc7lN7b_gqvdN6yFFxUbXt21O04i0RTIwLFF1ArBUxsHhA7HFluM09g%3D%3D&attredirects=0) Quote Share this post Link to post Share on other sites
Calvin19 0 #20 February 22, 2010 AWESOME! textbook root stall progression... win. Quote Share this post Link to post Share on other sites
Calvin19 0 #21 February 22, 2010 a very crude commonly observed example can be seen in some drainage troughs where water is poured into the diagonal trough. it splashes out to the sides, then converges, then spreads back out, then back in, every time the wave crests getting smaller. OR, under a faucet with a smal stream of water coming out, put your finger under the water near the faucet and you can see a surface tension version of a similar phenomenon. -SPACE- Quote Share this post Link to post Share on other sites
lawrocket 3 #22 February 22, 2010 I think that this is one of the coolest threads ever! Makes me wish I could go back to school to study engineering and physics. My wife is hotter than your wife. Quote Share this post Link to post Share on other sites
warpedskydiver 0 #23 February 22, 2010 I agree, my background in engineering has always helped me. My ability to visualize things like this has always been of great benefit. This is why we should encourage kids to be able to do such things, not everything comes from writing it on paper first. Quote Share this post Link to post Share on other sites
