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1/25/2018 7:38:29 AM
Posted: 7/8/2002 1:27:52 PM EST
Does this comply with the laws of physics, or is it just another urban legend? I was listening to a radio talk show recently. The host claims to have been a passenger on a commercial airliner several years ago. He indicated that the plane was apparently cruising (with the aid of a strong tailwind)at just one or two mph below the speed of sound. He claims that a small child ran up the aisle from coach to first class. In so doing the child broke the sound barrier, while the plane did not. He stated that there was a sonic boom and the child was thrown from his feet. I guess the two most basic questions that I have to ask are: 1. Is it possible for an airliner, other than the Concorde to approach the speed of sound? 2. If I run inside of a vehicle that is traveling at a certain speed, am I then traveling at the speed of the vehicle plus my own or only at the speed of the vehicle?
Link Posted: 7/8/2002 1:30:57 PM EST
the sound barrier is a function of the pressure of sound waves built up on the leading edge of a object, which happens to occur around a specific velocity. Inside of an airplane there is no way for this to occur, hence no sonic boom for little timmy!
Link Posted: 7/8/2002 1:33:12 PM EST
urban legend. The child is in a contained, pressurized system. While the child might "break the sound barrier" in relation to the ground and the outside environment while running, there would be no sonic boom. Something like that would have been plastered all over the news under the "odd but true" headline.
Link Posted: 7/8/2002 1:34:24 PM EST
Originally Posted By snailfan: I guess the two most basic questions that I have to ask are: 1. Is it possible for an airliner, other than the Concorde to approach the speed of sound? 2. If I run inside of a vehicle that is traveling at a certain speed, am I then traveling at the speed of the vehicle plus my own or only at the speed of the vehicle?
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1. theoretically, but not in practice. 2. yes, you are.
Link Posted: 7/8/2002 1:35:43 PM EST
Ha, ha! Now perhaps if the pilot had opened a window at that exact instance.... :)
Link Posted: 7/8/2002 1:36:31 PM EST
I call bullshit, I am no expert but since the inside of the plane is a nearly completely controlled environment there should be no dam of air in front of this little kid and there for it shouldn't have a sonic boom. this sounds like some bs he contrived in his head to keep you interested for a few seconds while the found the cd for the next song. either that or the dumb kid fell the same time some one dropped somthing. either way I don't think it quite happened that way. but like I said I am no genius ps. conscidering the sound barrier is somewhere over 700 mph, I somewhat dobt that any pilot would allow the plane to fly quite that fast. but I have much more experience in rotary wing aircraft so like I said I am not a qualified expert.
Link Posted: 7/8/2002 1:38:46 PM EST
Two things: 1. The speed of sound must be broken in the media the object is traveling in. Hence, the boy was traveling at two mph. 2. Commercial subsonic jets cannot get to 2 mph less than the speed of sound. Even if they could approach this speed, a slight push would get them to go transsonic, and would break the plane into a gillion pieces.
Link Posted: 7/8/2002 1:39:29 PM EST
just FYI, the speed of sound at 20C is approximately 770mph
Link Posted: 7/8/2002 1:43:36 PM EST
Here is a fun one for you. If little Jimmy is in a plane going the speed of sound - 2 MPH and runs towards the front of the plane at 3MPH, he has just broken the speed of sound relative to the ground, but relative to the plane he is going 3MPH. If he was on a spaceship going C (the speed of light) and ran towards the front of the craft, how fast would he be going? Please ignore the fact that he would be a waveform and contain infinite mass for the sake of argument.
Link Posted: 7/8/2002 1:43:52 PM EST
Couple of notes: (1) Speed of sound varies with density of the medium, and thus varies with altitude. (2) Commercial airliners (other than the Concorde) cannot get that close to the speed of sound. If, for example, they attempted this with a high speed dive, the plane would likely come apart. (3) As for the groundspeed being the plane's speed plus your speed, this is correct using a classical Newtonian mechanics approach. However, it does ignore relativistic effects, which would mean your actual speed would be very, very slightly slower than simply adding the 2 velocities. The difference at these speeds would make an RCH look like a tree trunk. [;)]
Link Posted: 7/8/2002 2:00:09 PM EST
[Last Edit: 7/8/2002 2:01:35 PM EST by Noname]
This is what Little Timmy would look like at speed...[img]http://home.pacbell.net/ok3/FA-18C.jpg[/img]
Link Posted: 7/8/2002 2:04:27 PM EST
I got the sheep skin so I wouldn't have to do these anymore. I will now have the nightmare about my final exam in the class that I enrolled in but never attended. THANKS A LOT
Link Posted: 7/8/2002 2:48:15 PM EST
Thanks for the informed responses. Now I'll finally be able to sleep.
Link Posted: 7/8/2002 3:22:54 PM EST
[Last Edit: 7/8/2002 3:42:12 PM EST by The_Emu]
Boy, where to start? First, the speed of sound is an AIR speed. that is a speed relative to the surrounding air. So if your average Boeing 757 is cruising at 500mph airspeed and there is a 100 mph tail wind then the Ground speed is 600mph but the AIR speed remains 500mph. so then if a person was running inside the airplane at 3mph toward the front of the plane the persons ground speed would be 603mph, but since the air inside the fuselage is pretty much still, the persons AIR speed would still be only 3mph. The idea that if an airliner would instantly break up if it went faster than the sound barrier is kind of "Hollywood". but it certainly isn't healthy for the airframe due to the changes in forces that occur in Trans-sonic speeds. Also weird things happen with the controls at these speed depending on the design of the control surfaces. the controls could become ineffective or even reverse. that's why modern airliners have a overspeed warning device. the really nice ones have a voice warning that will Say "Over Speed" warning the pilot to slow down. again this is all based on AIRspeed, not ground speed. Incidentally all airplanes have a published max speed (called Never excede Speed, Vne). its possible to dive just about any plane past that speed, but again it is 1.really hard on the airframe, 2.bad for the long-term life of the airplane, 3. dangerous (duh). if the plane enters turbulence or the pilot is rough on the controls, while going too fast, it could break.
Link Posted: 7/8/2002 3:27:12 PM EST
Originally Posted By Noname: This is what Little Timmy would look like at speed...[img]http://home.pacbell.net/ok3/FA-18C.jpg[/img]
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Cool pic!!!
Link Posted: 7/8/2002 3:40:06 PM EST
Originally Posted By poikilotrm: Here is a fun one for you. If little Jimmy is in a plane going the speed of sound - 2 MPH and runs towards the front of the plane at 3MPH, he has just broken the speed of sound relative to the ground, but relative to the plane he is going 3MPH. If he was on a spaceship going C (the speed of light) and ran towards the front of the craft, how fast would he be going? Please ignore the fact that he would be a waveform and contain infinite mass for the sake of argument.
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im fairly sure that his speed would remain C (the speed of light) i remember the answer, but not the reason (typical male, I know [;)])
Link Posted: 7/8/2002 3:44:49 PM EST
Originally Posted By The_Emu: The idea that if an airliner would instantly break up if it went faster than the sound barrier is kind of "Hollywood". but it certainly isn't healthy for the airframe due to the changes in forces that occur in Trans-sonic speeds. Also weird things happen with the controls at these speed depending on the design of the control surfaces. the controls could become ineffective or even reverse.
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Well, you were going ok until you hit that point. This was urban legend courtesy of Hollyweird. A movie released just before Chuck Yeager's sound-barrier-shattering flight had the pilot "reverse the controls" to survive his experience. Since people are idiots, they believed Hollyweird was portraying reality, when it was actually 100% bullshit. And the urban legend lives on. . . .
Link Posted: 7/8/2002 3:45:43 PM EST
Link Posted: 7/8/2002 3:56:34 PM EST
[Last Edit: 7/8/2002 3:58:17 PM EST by CITADELGRAD87]
Originally Posted By 71-Hour_Achmed:
Originally Posted By The_Emu: The idea that if an airliner would instantly break up if it went faster than the sound barrier is kind of "Hollywood". but it certainly isn't healthy for the airframe due to the changes in forces that occur in Trans-sonic speeds. Also weird things happen with the controls at these speed depending on the design of the control surfaces. the controls could become ineffective or even reverse.
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Well, you were going ok until you hit that point. This was urban legend courtesy of Hollyweird. A movie released just before Chuck Yeager's sound-barrier-shattering flight had the pilot "reverse the controls" to survive his experience. Since people are idiots, they believed Hollyweird was portraying reality, when it was actually 100% bullshit. And the urban legend lives on. . . .
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INCORRECT. In the B47, with it's thin, long swept wing, control reversal at near mach speeds was...[size=3]FACT[/size=3]. The aileron warped the wing, causing the opposite of the control input into the yoke. My dad told me many times about the phenominon of control reversal. Edited to add: My near constant references to my dad are just a reflection of his greateer experiences than mine. He retired after 32 years in the AF, and that was 10 years ago, you do the math, I'm no teenager.
Link Posted: 7/8/2002 4:00:39 PM EST
On a related issue: Ever see those executive mini-jets? Couple mil' each. Rock stars and CEO's buy them for themselves as a partial tax shelter. Well, for those of you that don't already know, alcohol and general aviation have a long history. Those Cessna's you see wobbling overhead aren't always doing so because of wind shear. Anyhow, those mini-jets have a top speed of ~.85% of sound. After a few drinks several pilot/owners have had the bright idea of breaking the sound barrier just like Gen. Chuck Yeager. Except they have to put their planes into a dive to go that fast. The problem they encounter is that those planes aren't designed to go supersonic, no matter how cool they look. Talk about a rough ride. That'll sober you up fast. Dopes.
Link Posted: 7/8/2002 4:17:51 PM EST
[Last Edit: 7/8/2002 4:21:13 PM EST by The_Emu]
its been a few years since i took aerodynamics, i'll have to check with my copy of [i]Aerodynamics for Naval Aviators[i/] No, i wasnt in the navy, its just a good text book.
Link Posted: 7/8/2002 4:23:26 PM EST
There was a similar thread on the issue of "relativity" and the speed of objects relating to the speed of light a while back and this is pure urban legend. Like Einstein says all motion is relative. The fact that the the aircraft is at mach threshold has no bearing on the fact that the boy is running at mach. Even though from a stationary observer the boy would in fact be traveling supersonic but in order for him to break the sound barrier HE would have to run at mach 1. Why so? Well the aircraft is traveling through the atmosphere at near mach and the sonic boom is a result of a pressure wave forming on the aircraft as the plane basically moves faster than the air can get out of it's way. The people inside however are not acting against the outside atmosphere but rather the "relatively" stationary air inside the cabin. So in this instance there is some truth. The boy, in theory, could, to a strategically placed stationary observer, be traveling supersonic but such an instance is only a theoretical one and unlikely in practicality. Now what do you think would happen to a pressurized cabin at 30,000 ft if a human sized object were to be able to somehow go supersonic within the confines of the fuselage? As for the unreliable controls of some aircraft at transonic speeds I think it has something to do with the "mach cone" that is created and is directly related to the velocity and geometry of said aircraft. I think it is neccessary for an aircraft to fly inside of it's own mach cone(think long slender SR-71) If enough of the control surfaces(wings, elevator, rudder etc.) of the plane extend beyond that barrier a situation can arise where the difference in airflow can disrupt the function of the airfoil. There is also a phenomena called inertial lock I believe which is basically loss of control because the air foils are not sufficient to overcome the inertia of an aircraft at near mach and mach speeds. This is why the elevators on supersonic birds rotate at the tail instead of a moving trailing edge that doesn't have enough aerodynamic effect. Couple this with the effects of the "mach cone" and a plane can become very unstable attaining mach speed. But I may be completely wrong here.
Link Posted: 7/8/2002 4:30:59 PM EST
poikilotrm The speed of light is the exception to Relativity and it is covered in Special Relativity... I think... Anyway "C" is constant(in a vacuum) no matter the position or velocity of the observer.
Link Posted: 7/8/2002 4:37:01 PM EST
Originally Posted By poikilotrm: Here is a fun one for you. If little Jimmy is in a plane going the speed of sound - 2 MPH and runs towards the front of the plane at 3MPH, he has just broken the speed of sound relative to the ground, but relative to the plane he is going 3MPH. If he was on a spaceship going C (the speed of light) and ran towards the front of the craft, how fast would he be going? Please ignore the fact that he would be a waveform and contain infinite mass for the sake of argument.
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Funny question, but invalid--the spaceship, having mass, cannot travel at C.
Link Posted: 7/8/2002 5:35:41 PM EST
[Last Edit: 7/8/2002 5:44:12 PM EST by prk]
I think the host just made that crap up to see how gullible his listeners are. Since you didn't mention him getting a mess of calls telling him what an idiot he was, I have to wonder if he didn't prove his theory (of a gullible audience). The speed of the plane has absolutely NOTHING NOTHING to do with whether the fictional kid broke the sound barrier. Unless he was outside, standing on the fuselage, and had enough leg power to run forward (which would of course be anatomically impossible). Inside the airplane, the air was for all purposes at a standstill, relative to this imaginary boy, then when "he" "ran", he managed to get up to, say, 3 mph relative to the air in the cabin. The air outside the cabin is irrelevant. Now, as far as light is concerned, theoretical physics gives it different properties than sound, not just because it can travel through a vacuum, but fundamentally they (used to, at least) say that light can not travel any faster than the 186,000 miles per second, and that this is true because of particle/quantuum/whatever physics and the very nature of matter and energy. It's been my belief for a long time that this is utter bullshit, and an example of why you shouldn't place too much faith in science. That if you were travelling at 99% the speed of light, you could STILL get a fine beam from your Surefire. Problem is, I can't prove it, and physicists are a lot better at arguing in their own realm than I am. So I would like to see them prove it experimentally, with a live observer in, say a space craft. If you could get to 50% the speed of light, there should be a noticable effect, if they're correct. Of course we haven't figured out how to do this, yet. So they have tried to design clever experiments using rockets and lasers and solar eclipses and all sorts of things, to "prove" Einstein's work. They even figured they could tweak measurements to correct for the doppler shift of light coming down from the rocket that was caused by Earth's gravity acting on the light, and all sorts of stuff. My belief is that in those experiments, there was some (or a lot of) circular reasoning that I can't put my finger on, in all their corrections and assumptions, etc. Problem is, you have to be pretty strong in physics to make reasoned arguments about this stuff. Even though this is supposed to be "hard science", I think recently some of the physicists have decided that faster than light travel is not theoretically impossible, or at least is worth some serious theoretical work. For the lay person with an intuitive belief that science has goofed, this kind of argument can start to share some of the same dynamics as the Evolution vs. Creation wars. I'm not going to argue more about ANYTHING here, or respond to any further posts. Just want to encourage people to question what they hear / read.
Link Posted: 7/8/2002 5:39:00 PM EST
maybe the kid just farted real loud and his dad covered for him saying it was a sonic boom
Link Posted: 7/8/2002 5:58:06 PM EST
Originally Posted By poikilotrm: Here is a fun one for you. If little Jimmy is in a plane going the speed of sound - 2 MPH and runs towards the front of the plane at 3MPH, he has just broken the speed of sound relative to the ground, but relative to the plane he is going 3MPH. If he was on a spaceship going C (the speed of light) and ran towards the front of the craft, how fast would he be going? Please ignore the fact that he would be a waveform and contain infinite mass for the sake of argument.
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Stoppit, wouldya?
Link Posted: 7/8/2002 6:05:14 PM EST
I am laughing at some of y'all's superior intellect! [:D] (you know who you are) You need hip waders to get thru some of the physics posted here! I'll only say this: urban legend, no boom, inertial frame, and y'all einstein-wannabes forget the dayum relativity because the vee-pee is a lotta-mo less than cee, so it don't apply! Funny anyway! [beer]
Link Posted: 7/8/2002 6:10:27 PM EST
Wow! All these theoretical postulations about the speed of light and such. Harkens me back to the days when I used to wonder about what existed before the beginning of the universe. Now I seem to be more concerned about what's for dinner tonight or whether or not the Hurricanes can win the Stanley Cup next year. I think I'm definitely getting dumber. Oh well, ignorance is bliss, right?
Link Posted: 7/8/2002 8:22:03 PM EST
Wasn't it some British transport pilot chick?
Link Posted: 7/8/2002 8:51:13 PM EST
Which one breaks the speed of sound? A) Timmy running 3 mph in a plane traveling Mach -2. B) .45 cal ball leaving the muzzle of a 1911 pistol. C) Cracking a whip. D) A bullet fired vertically after apogee. F) An AR-15 fired downward into a body of water with the muzzle in contact with the surface.
Link Posted: 7/8/2002 9:00:25 PM EST
Link Posted: 7/8/2002 9:22:33 PM EST
Here's an obscure little tidbit. Who was the first human to travel at transonic speeds in [b]FREEFALL[/b]????? Scott
Link Posted: 7/8/2002 9:35:06 PM EST
[Last Edit: 7/8/2002 9:37:13 PM EST by kpel308]
Link Posted: 7/9/2002 1:02:15 AM EST
This all reminds me of the time I was travelling to Europe on the Concorde jet. Not thinking about the fact that we were travelling faster than the speed of sound, I became increasingly alarmed when the people in the seats ahead of me started speaking with higher and higher pitched voices. Finally, I turned around to a gentleman sitting directly behind be and asked him if he noticed anything strange going on. He appeared to answer me, but I could not hear any sounds coming from his mouth. I began to feel really sick at this point, and headed for the restroom at the rear of the jet. This was a MAJOR mistake. There was such an accumulated buildup of words and noises plastered against the back wall of the passenger compartment that it almost blew my eardrums out. Though once I got into the restroom, shut the door and flushed the toilet once, things quieted right down.
Link Posted: 7/9/2002 2:49:48 AM EST
I have been on airliners were a small child broke my sound barrier! I offered to rock the baby to eliminate the sound. But do you realize how hard it is to find a big rock on a airplane!
Link Posted: 7/9/2002 3:01:40 AM EST
Well, I experienced something weird on a plane once that makes me think its true. I was flying out of Nashville. We WERE travelling just under the speed of sound, the pilot said so, we couldnt go any faster because of FAA regulations. Anyhow, a little girl did start to run up to the front of the plane. She must have reached the speed of sound because BAM! someone stole her kidneys.
Link Posted: 7/9/2002 11:20:42 PM EST
[Last Edit: 7/9/2002 11:22:10 PM EST by DScottHewitt]
Originally Posted By kpel308: Air Force Colonel Joe Kittinger, jumping from a helium balloon that was at 100,000 ft. ASL. He broke the sound barrier in only a pressure suit from free fall. After Project: SkyHook, he went on to fly SuperSabres in the RVN. Edited to add that he is the only individual to have earned Astronaut wings in a balloon.
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Gee, I thought that would a little more obscure..... [url]http://www2.tsixroads.com/Corinth_MLSANDY/jk028.html[/url] Scott [beer]
Link Posted: 7/9/2002 11:32:20 PM EST
Fuzzbean, Avtomat You crock me up!
Link Posted: 7/10/2002 10:21:46 AM EST
Link Posted: 7/10/2002 10:51:11 AM EST
Actually, more than a few commercial jets and bizjets have been in the transonic speed range and did not break up. Controls get very unstable to different degrees depending on the airframe and how suited it is to airflow at transsonic and sonic velocities. There was a fairly detailed article on this in Smithsonian Air and Space magazine several years ago. The article mentioned a Boeing 7-something or other that was tested intentionally at transonic velocities to determine control response. The article further mentioned some bizjets that are rated for close to Mach 1, and cited some cases where they were flown at M1 or just above. Noah
Link Posted: 7/10/2002 11:12:23 AM EST
I have not read any of the other replies yet, so others have probably said it before me...
Originally Posted By snailfan: Does this comply with the laws of physics, or is it just another urban legend?
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The laws of physics are always complied with! [;)] One way or another
I was listening to a radio talk show recently. The host claims to have been a passenger on a commercial airliner several years ago. He indicated that the plane was apparently cruising (with the aid of a strong tailwind)at just one or two mph below the speed of sound. He claims that a small child ran up the aisle from coach to first class. In so doing the child broke the sound barrier, while the plane did not. He stated that there was a sonic boom and the child was thrown from his feet.
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Utter bullshit. Sound can only travel in a medium because it is a pressure wave. Pressure waves are what happens when particles slam into each other. Thus the speed of sound is relative to the speed of the medium. If you are in a car driving 100 MPH, and your windows are up, the air in the car is still. Thus this becomes the new reference point for the speed of sound. Even if you were going exactly the speed of sound, the air in the car would be still, thus someone in the backseat would still be heard by someone in the front. Light is an entirely different animal however.
I guess the two most basic questions that I have to ask are: 1. Is it possible for an airliner, other than the Concorde to approach the speed of sound?
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Yes, easily. Commercial jets typically fly 80%-85% Mach, and Business jets can get closer to 93%-97% Mach in level flight. In a powered dive, Any commercial jet can hit Mach 1. Not a good idea to try however.
2. If I run inside of a vehicle that is traveling at a certain speed, am I then traveling at the speed of the vehicle plus my own or only at the speed of the vehicle?
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Yes again. Velocities are additive. That is why it is so much fun to run up an escalator or ride a bike on a treadmill!
Link Posted: 7/10/2002 11:17:42 AM EST
If a deaf bear farts in the woods, did it really make a sound????
Link Posted: 7/10/2002 11:55:44 AM EST
Originally Posted By marvl: (2) Commercial airliners (other than the Concorde) cannot get that close to the speed of sound. If, for example, they attempted this with a high speed dive, the plane would likely come apart.
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Hasn't the Citation X flown faster than the speed of sound? I think Steven Fossett did a flight once averaging 700 mph.
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