here is some work i produced over the fourth of july holiday, due to a cool question i was asked, by a former co-worker...here goes( posted from my facebook)--
A
holiday engineering question...i had a coworker ask me a question
regarding why a gun shot's report has no echo at all, while the sound of
a fireworks boom produces one...i thought about it, and here is what i
said...
The echo--
I believe that an echo is a model similar to the dynamics we observe when we drop a pebble in the center of a puddle of water...the wave generated moves outward in an equal manner, from the center of "the-point-of-origin", in an equal pattern, moving from the center, outward, 360 degrees from the "point-of-origin", until it "crests", and reaches the edge of the puddle of water, at this point, the wave returns to the center of the puddle, to the "point-of-origin", and i feel that this natural model is congruent with the dynamics in play from a fireworks explosion on the forth of july...the sound wave from the explosion moves outward, from the "point-of-origin", in an equal manner, and strikes all of the objects it encounters "squarely", or "at a 90 degree angle", i suggest that this results in the sound wave being reflected directly back, in the precise direction in which it came, in each degree, of the 360 degrees from the "point-of-origin", producing an "echo"...
The gun-shot/"report"--
I feel that the difference in results produced, from the two different physical models/actions, is essentially about the inequality of the movement of the sound waves, traveling outward, from the two actions...the gun shot produces sound from the gasses of the "report", exiting the gun's barrel, when the shot is fired...in more of a "cone-shape", that moves in the direction of the shot fired, and not equally, as we see in the "pebble-in-a-puddle" model, yes, there is some sound that moves from the side of the barrel during the gun shot, but not much, compared to the direction of the shot, and not in an equal manner, as seen in the "pebble-in-a-puddle" model...this results in the vector of the gun shot's sound wave contacting objects at an angle that does not refract/reflect the sound wave directly back in the opposite direction, back towards the "point-of-origin", and instead, the sound wave is reflected back indirectly, producing no echo...also, and mainly, the "report" of the gun shot does not travel outward from the "point-of-origin" in an equal pattern, as we see in the "pebble-in-a-puddle" model, and this means that the sound wave does not get refracted directly back to the wave's starting point, to generate an echo...lastly, the bullet fired sometimes breaks the speed of sound, and i feel that this must be considered, due to the action of the sound barrier being broken producing a sound, leading me to speculate on the precise dynamics "in-play" when the sound barrier is broken...
The sound barrier--
I suggest that the sound we hear when the sound barrier is breached, is readily seen in nascar racing, and a few automotive commercials...here goes...
In the car commercials most of us have seen on television, the low-speed stream of smoke in the wind-tunnel, goes over the cars contours very closely, displaying the cars "drag", or "air-foil" , very well, and i suggest, that this physical model is simply expressing the phenomenon ongoing with "drag", and "drafting", in nascar racing, and also the sound barrier...in nascar racing, at speeds above 150 mph, all nascar drivers know, that the air that contacts the front windshield, moves over the roof, and then passes mostly straight backwards, and does not follow the contours of the race car very closely, there is some pressure exerted against the trunk, and the rear fin of the car, adding downward force, to the rear-end of the vehicle, and the faster you go, the more pressure is generated against the trunk lid, from the air-stream of the air moving around the car's contour, moving "tighter", or more closely, to the body of the car, following the shape of the car, more forcefully, and closer...i believe this known concept is the key to understanding the sound barrier, and why it produces a sound when breached, as well as why there is not a second "sonic-boom", and why airplanes fly faster after the speed of sound is breached, with less effort, exerted by the engines to do so...
The skinny--
I suggest, that an airplane is a congruent model, both to the auto commercial, and the race car, the speed being traveled is merely much greater, and, this increased speed, increases the pressures of air, both against the contours of the hull of the craft, and also to the "draft pocket", that is also present behind a race car...allowing a competing car, traveling directly behind it, to travel faster, without using the power of the engine very much...essentially, the lead nascar racer has a "vacuum" behind it, and this limits the speed of the lead car, due to this "vacuum" acting on the rear of the car, slowing it( while the driver traveling a few feet behind, is not slowed, resulting in extra power to pass the lead car, from the engine doing less work, to maintain the speed, with less gas expended to do so)...i believe that this dynamic is also "in play", while an airplane flies, and i suggest, that the pocket of negative air pressure( "draft pocket"), located directly behind an airplanes wings, and tail, get more, and more, pressure from the air-stream of the jet, until the air moving around the top of the plane, and the air moving across the bottom of the fuselage, slam together, after the craft's "draft-pocket" collapses...popping, like a piece of "bubble-wrap", and making a huge "sonic boom", this concept describes/represents the air-stream of the air moving around the planes exterior, being so tight to the fuselage, that there is no longer a "draft-pocket" behind the airplanes wings, and tail, since the air-foil of the plane is too close to the exterior of the plane, and as a result, there is no "vacuum" acting on the trailing surfaces of the craft, slowing it, from the negative pressure within the "draft-pocket", essentially "sucking" the plane backwards, and reducing the effectiveness of the engines thrust...meaning...once the air-stream of the air passing over the plane has been pulled this close to the body of the craft( from increased speed), and the "draft pocket" has collapsed, there can be no further "sonic booms" produced, and the aircraft may speed up above mock-1, unencumbered by the "drag"of the airplane's "drag-pocket", after it has collapsed...lastly, i feel that we must examine the shape of, and true natural reasons for, the "draft-pocket" to exist at all--
The draft pocket--
I feel that the "draft pocket" is best physically described, and displayed, by examining the air movement, and shape, of a hot air balloon...cold air enters the opening, above the basket, at the rim, and warm air comes out of the direct center of the opening, acting like a rudimentary jet engine, that works based upon the "venturi shape" of the balloon, and the cold air( lesser concentration of molecular collisions per-sec), attempting to equalize in temp, with the hot air trapped inside the balloon( with a greater concentration of molecular collisions per-sec), so, again...i believe that the cold air outside the balloon, moves into the balloon at the rim of the balloon's opening, then it increases in speed, from encountering the curve/vector of the balloon's "neck", or "venturi", where it mixes with the air at the "bulb", or top, of the balloon, forcing some of the air out of the center of the balloons opening, above the basket...and, if we view this physical model, working on it's side, directly behind an airplane's tail, and wings, i believe we will have an accurate description of the "draft pocket", in action...i suggest that the speed of the air rushing by the tail( but not perfectly close to the tails' surfaces), allows an "air-pocket" to exist directly behind the tail...air is drawn away from this area, to mix with the air-stream that is coming from above, and below, the airplane, streaming off the tail of the craft...i feel that this motion of air, is best described as air moving in, towards the tail, and then turning abruptly around, and going the opposite way, to join with the "jet-wash" of the aircraft...in the same manner as a hot air balloon's air movement does( inverted, with air entering at the center, and exiting at the rim)..in this case, of the aircraft's "draft-pocket", i feel that the key concept to grasp, is in relation to a nascar racer's rear spoiler, and trunk-lid...if we view the aircraft's "draft-pocket", as an extension of a race car's trunk-lid, we will readily see that the "draft-pocket" is also incurring more, and more, pressure, like the trunk-lid of the race car does...and i feel that this dynamic forces the "neck" of the "balloon shape" of the "draft-pocket" to narrow, more, and more, until the "neck" of the "draft-pocket" is forced closed...and at this time, we have arrived at the critical speed/moment, when any additional air pressure from the "jet-wash" of the aircraft, ruptures the sealed "draft-pocket", of negative air pressure( located directly behind the airplane's wings/tail)...and BOOM...the craft has broken the sound barrier...way to go Chuck...history is made( i believe that this concept readily describes the true reason Mr Yeager experienced mild/major buffeting of his "elevators", during his flight, due to a "draft-pocket" being directly behind each of his wings, that became massively turbulent, right before he breached the barrier, resulting in his "elevators" "wagging", like the tail of a dog, sending reverse control movements back through his aircraft's control rods, to the "stick", or wheel--
i feel that this B.S., is good B.S., of use for scientists, and airmen, to speculate about...and nothing more...
best wishes, john kruschke--
The echo--
I believe that an echo is a model similar to the dynamics we observe when we drop a pebble in the center of a puddle of water...the wave generated moves outward in an equal manner, from the center of "the-point-of-origin", in an equal pattern, moving from the center, outward, 360 degrees from the "point-of-origin", until it "crests", and reaches the edge of the puddle of water, at this point, the wave returns to the center of the puddle, to the "point-of-origin", and i feel that this natural model is congruent with the dynamics in play from a fireworks explosion on the forth of july...the sound wave from the explosion moves outward, from the "point-of-origin", in an equal manner, and strikes all of the objects it encounters "squarely", or "at a 90 degree angle", i suggest that this results in the sound wave being reflected directly back, in the precise direction in which it came, in each degree, of the 360 degrees from the "point-of-origin", producing an "echo"...
The gun-shot/"report"--
I feel that the difference in results produced, from the two different physical models/actions, is essentially about the inequality of the movement of the sound waves, traveling outward, from the two actions...the gun shot produces sound from the gasses of the "report", exiting the gun's barrel, when the shot is fired...in more of a "cone-shape", that moves in the direction of the shot fired, and not equally, as we see in the "pebble-in-a-puddle" model, yes, there is some sound that moves from the side of the barrel during the gun shot, but not much, compared to the direction of the shot, and not in an equal manner, as seen in the "pebble-in-a-puddle" model...this results in the vector of the gun shot's sound wave contacting objects at an angle that does not refract/reflect the sound wave directly back in the opposite direction, back towards the "point-of-origin", and instead, the sound wave is reflected back indirectly, producing no echo...also, and mainly, the "report" of the gun shot does not travel outward from the "point-of-origin" in an equal pattern, as we see in the "pebble-in-a-puddle" model, and this means that the sound wave does not get refracted directly back to the wave's starting point, to generate an echo...lastly, the bullet fired sometimes breaks the speed of sound, and i feel that this must be considered, due to the action of the sound barrier being broken producing a sound, leading me to speculate on the precise dynamics "in-play" when the sound barrier is broken...
The sound barrier--
I suggest that the sound we hear when the sound barrier is breached, is readily seen in nascar racing, and a few automotive commercials...here goes...
In the car commercials most of us have seen on television, the low-speed stream of smoke in the wind-tunnel, goes over the cars contours very closely, displaying the cars "drag", or "air-foil" , very well, and i suggest, that this physical model is simply expressing the phenomenon ongoing with "drag", and "drafting", in nascar racing, and also the sound barrier...in nascar racing, at speeds above 150 mph, all nascar drivers know, that the air that contacts the front windshield, moves over the roof, and then passes mostly straight backwards, and does not follow the contours of the race car very closely, there is some pressure exerted against the trunk, and the rear fin of the car, adding downward force, to the rear-end of the vehicle, and the faster you go, the more pressure is generated against the trunk lid, from the air-stream of the air moving around the car's contour, moving "tighter", or more closely, to the body of the car, following the shape of the car, more forcefully, and closer...i believe this known concept is the key to understanding the sound barrier, and why it produces a sound when breached, as well as why there is not a second "sonic-boom", and why airplanes fly faster after the speed of sound is breached, with less effort, exerted by the engines to do so...
The skinny--
I suggest, that an airplane is a congruent model, both to the auto commercial, and the race car, the speed being traveled is merely much greater, and, this increased speed, increases the pressures of air, both against the contours of the hull of the craft, and also to the "draft pocket", that is also present behind a race car...allowing a competing car, traveling directly behind it, to travel faster, without using the power of the engine very much...essentially, the lead nascar racer has a "vacuum" behind it, and this limits the speed of the lead car, due to this "vacuum" acting on the rear of the car, slowing it( while the driver traveling a few feet behind, is not slowed, resulting in extra power to pass the lead car, from the engine doing less work, to maintain the speed, with less gas expended to do so)...i believe that this dynamic is also "in play", while an airplane flies, and i suggest, that the pocket of negative air pressure( "draft pocket"), located directly behind an airplanes wings, and tail, get more, and more, pressure from the air-stream of the jet, until the air moving around the top of the plane, and the air moving across the bottom of the fuselage, slam together, after the craft's "draft-pocket" collapses...popping, like a piece of "bubble-wrap", and making a huge "sonic boom", this concept describes/represents the air-stream of the air moving around the planes exterior, being so tight to the fuselage, that there is no longer a "draft-pocket" behind the airplanes wings, and tail, since the air-foil of the plane is too close to the exterior of the plane, and as a result, there is no "vacuum" acting on the trailing surfaces of the craft, slowing it, from the negative pressure within the "draft-pocket", essentially "sucking" the plane backwards, and reducing the effectiveness of the engines thrust...meaning...once the air-stream of the air passing over the plane has been pulled this close to the body of the craft( from increased speed), and the "draft pocket" has collapsed, there can be no further "sonic booms" produced, and the aircraft may speed up above mock-1, unencumbered by the "drag"of the airplane's "drag-pocket", after it has collapsed...lastly, i feel that we must examine the shape of, and true natural reasons for, the "draft-pocket" to exist at all--
The draft pocket--
I feel that the "draft pocket" is best physically described, and displayed, by examining the air movement, and shape, of a hot air balloon...cold air enters the opening, above the basket, at the rim, and warm air comes out of the direct center of the opening, acting like a rudimentary jet engine, that works based upon the "venturi shape" of the balloon, and the cold air( lesser concentration of molecular collisions per-sec), attempting to equalize in temp, with the hot air trapped inside the balloon( with a greater concentration of molecular collisions per-sec), so, again...i believe that the cold air outside the balloon, moves into the balloon at the rim of the balloon's opening, then it increases in speed, from encountering the curve/vector of the balloon's "neck", or "venturi", where it mixes with the air at the "bulb", or top, of the balloon, forcing some of the air out of the center of the balloons opening, above the basket...and, if we view this physical model, working on it's side, directly behind an airplane's tail, and wings, i believe we will have an accurate description of the "draft pocket", in action...i suggest that the speed of the air rushing by the tail( but not perfectly close to the tails' surfaces), allows an "air-pocket" to exist directly behind the tail...air is drawn away from this area, to mix with the air-stream that is coming from above, and below, the airplane, streaming off the tail of the craft...i feel that this motion of air, is best described as air moving in, towards the tail, and then turning abruptly around, and going the opposite way, to join with the "jet-wash" of the aircraft...in the same manner as a hot air balloon's air movement does( inverted, with air entering at the center, and exiting at the rim)..in this case, of the aircraft's "draft-pocket", i feel that the key concept to grasp, is in relation to a nascar racer's rear spoiler, and trunk-lid...if we view the aircraft's "draft-pocket", as an extension of a race car's trunk-lid, we will readily see that the "draft-pocket" is also incurring more, and more, pressure, like the trunk-lid of the race car does...and i feel that this dynamic forces the "neck" of the "balloon shape" of the "draft-pocket" to narrow, more, and more, until the "neck" of the "draft-pocket" is forced closed...and at this time, we have arrived at the critical speed/moment, when any additional air pressure from the "jet-wash" of the aircraft, ruptures the sealed "draft-pocket", of negative air pressure( located directly behind the airplane's wings/tail)...and BOOM...the craft has broken the sound barrier...way to go Chuck...history is made( i believe that this concept readily describes the true reason Mr Yeager experienced mild/major buffeting of his "elevators", during his flight, due to a "draft-pocket" being directly behind each of his wings, that became massively turbulent, right before he breached the barrier, resulting in his "elevators" "wagging", like the tail of a dog, sending reverse control movements back through his aircraft's control rods, to the "stick", or wheel--
i feel that this B.S., is good B.S., of use for scientists, and airmen, to speculate about...and nothing more...
best wishes, john kruschke--
