Some thoughts on sound...
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Some thoughts on sound...
I was thinking about the fact that there's no sound in space, as there's no medium (air) for it to pass through. Which led me to ask what it was that produced the sound in the first place - and my answer was 'movement'. Can anyone confirm this...?
So a moving body imparts a bunch of energy onto it's surrounding environment, part of which is sound. Now, say a space craft imparts 100 units of energy, 10 units of which are sound (as the craft goes through the atmosphere and into orbit), and the other 90 units as whatever.
So the craft is in space now (free from the earths atmosphere), I would expect it would still impart 100 units of energy to the imediate environment. But it obviously isn't going to be sound... I thought initially it could be heat, but there's nothing to conduct it too...
So where does the energy go?
Does the craft itself absorb it in some way?
Does it even produce the energy...?
Turbofan
P.S. Amazing the things you think of when you're trying to get to sleep...
So a moving body imparts a bunch of energy onto it's surrounding environment, part of which is sound. Now, say a space craft imparts 100 units of energy, 10 units of which are sound (as the craft goes through the atmosphere and into orbit), and the other 90 units as whatever.
So the craft is in space now (free from the earths atmosphere), I would expect it would still impart 100 units of energy to the imediate environment. But it obviously isn't going to be sound... I thought initially it could be heat, but there's nothing to conduct it too...
So where does the energy go?
Does the craft itself absorb it in some way?
Does it even produce the energy...?
Turbofan
P.S. Amazing the things you think of when you're trying to get to sleep...
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Turbofan
Sir Isaac Newton's three laws of motion should explain this. Also it's patently bleeding obvious :-}
The momentum of an object is constant unless an outside force acts on that obejct.
If the spacecraft is in the atmosphere, it requires thrust to maintain it's velocity or to accelerate. Just like an aircraft, in steady level flight, thrust = drag
In space....no one can hear you scream. And of course a body will continue in a straight line and at a constant velocity unless outside forces, (gravity, asteroids, green people) influence it.
Sir Isaac Newton's three laws of motion should explain this. Also it's patently bleeding obvious :-}
The momentum of an object is constant unless an outside force acts on that obejct.
If the spacecraft is in the atmosphere, it requires thrust to maintain it's velocity or to accelerate. Just like an aircraft, in steady level flight, thrust = drag
In space....no one can hear you scream. And of course a body will continue in a straight line and at a constant velocity unless outside forces, (gravity, asteroids, green people) influence it.
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I know what you're saying. It will still produce the same amount of energy, and the vibration of the airframe that would have produced sound will clearly not result in a vibration travelling through the surrounding medium (since there is none). This is not particularly significant to the aircraft, because all this would do in air is damp the vibration in the airframe *slightly*, while the rest of the energy would be converted to heat in the process of fatiguing the airframe. I would conclude then that in space, the rest of the energy that would have produced sound would be converted to heat and dissipated by E-M radiation.
Pie
[This message has been edited by Pielander (edited 27 June 2001).]
Pie
[This message has been edited by Pielander (edited 27 June 2001).]
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Strewth!!
How did you guys ever graduate from Starfleet academy?
Space is empty. A vaccuum. There's nothing there. It is a void. Zilch. Nothing. Devoid of matter. Lacking substance. Vacant, Unfilled. Bare. Blank. Unoccupied. It is bleedin.....space.
Therefore there is no friction. No drag. Nothing to conduct sound or vibration. Nothing to absorb energy.
If it is producing thrust it will accelerate. If it isn't it will continue in a straight line until it is influenced by an external force. (see above)
How did you guys ever graduate from Starfleet academy?
Space is empty. A vaccuum. There's nothing there. It is a void. Zilch. Nothing. Devoid of matter. Lacking substance. Vacant, Unfilled. Bare. Blank. Unoccupied. It is bleedin.....space.
Therefore there is no friction. No drag. Nothing to conduct sound or vibration. Nothing to absorb energy.
If it is producing thrust it will accelerate. If it isn't it will continue in a straight line until it is influenced by an external force. (see above)
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Bally Heck
We're not arguing with Sir Isaac. I realise how a momentum balance works, but the original question was nothing to do with that. It was about what happens to the proportion of 'waste energy' which, within the atmosphere, would normally be dissipated as sound. (From a jet/rocket engine [delete where inappropriate], that is - not from some sort of wind-rush noise, which I realise will be non-existent.)
My answer is that the vibration is damped by internal cyclic stresses of the structure, converted to heat, and radiated out into space.
Please explain to me how this conveys a lack of understanding of Newtonian physics.
Pie
[This message has been edited by Pielander (edited 27 June 2001).]
We're not arguing with Sir Isaac. I realise how a momentum balance works, but the original question was nothing to do with that. It was about what happens to the proportion of 'waste energy' which, within the atmosphere, would normally be dissipated as sound. (From a jet/rocket engine [delete where inappropriate], that is - not from some sort of wind-rush noise, which I realise will be non-existent.)
My answer is that the vibration is damped by internal cyclic stresses of the structure, converted to heat, and radiated out into space.
Please explain to me how this conveys a lack of understanding of Newtonian physics.
Pie
[This message has been edited by Pielander (edited 27 June 2001).]
Guest
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Ah. Er. Um.
Sorry Pielander. I'm with you now. Yep I guess internal vibration would be damped out by friction in the structure of the vessel which would be dissipated in the form of radiated heat. This is also what happens in the flying machines which you earthlings use.
RTFQ as my old drill sergeant used to say to me. I hope Jean Luc didn't see this posting.
Sorry Pielander. I'm with you now. Yep I guess internal vibration would be damped out by friction in the structure of the vessel which would be dissipated in the form of radiated heat. This is also what happens in the flying machines which you earthlings use.
RTFQ as my old drill sergeant used to say to me. I hope Jean Luc didn't see this posting.
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Nearly all of the noise from a spacecraft is produced in the vortex sheet between the rocket eflux and the ambient air. This is predominantly a quadripole source of noise from the fluctuating stresses in the vortices.
In space there is no vortex generation and the gases continue in uniform motion, any turbulence source of noise would dissipate in the expanding gas. The acoustic energy is vastly smaller than the kinetic energy of the gas and has no noticeable effect on performance.
Noise propogating through vibrating panels is of little significance, and in space there would just be a change in the panels impedance and the energy would be reflected back and dissipated internally.
In space there is no vortex generation and the gases continue in uniform motion, any turbulence source of noise would dissipate in the expanding gas. The acoustic energy is vastly smaller than the kinetic energy of the gas and has no noticeable effect on performance.
Noise propogating through vibrating panels is of little significance, and in space there would just be a change in the panels impedance and the energy would be reflected back and dissipated internally.
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Turbofan.
We now reach the first law of thermodynamics which roughly states that the energy in a system remains constant but that the form of the energy may be transformed.
The total energy of the system equals the internal energy, which depends only on the thermodynamic state, plus the kinetic energy, which depends on the system's motion, plus the potential energy, which depends on the system's position with respect to the chosen coordinate frame.
Kinetic energy (ie. vibration) may be converted to heat energy. Strike a piece of metal on an anvil for a few minutes and it's temperature will rise. Likewise a bicycle pumps motion produces heat due to the compression of the air.
Thus the vibration of your spacecraft will convert into a temperature increase as molecules and components move. Next time you destroy a credit card, bend it repeatedly and see how it gets warm at the fold.
If there is a heat gradient between the spacecraft and space. ie one is hot and the other cold, this heat energy will radiate from the spacecraft into space in the same way as it radiates from the bar of an electric fire. The rate of radiation is proportional to the square of the difference in temperatures, so a very hot body will begin cooling very quickly but the rate of cooling will reduce as the temperature difference reduces.
Having said all that....the thing would have to be shaking like a dance floor during an earthquake to produce appreciable amountsd of heat.
We now reach the first law of thermodynamics which roughly states that the energy in a system remains constant but that the form of the energy may be transformed.
The total energy of the system equals the internal energy, which depends only on the thermodynamic state, plus the kinetic energy, which depends on the system's motion, plus the potential energy, which depends on the system's position with respect to the chosen coordinate frame.
Kinetic energy (ie. vibration) may be converted to heat energy. Strike a piece of metal on an anvil for a few minutes and it's temperature will rise. Likewise a bicycle pumps motion produces heat due to the compression of the air.
Thus the vibration of your spacecraft will convert into a temperature increase as molecules and components move. Next time you destroy a credit card, bend it repeatedly and see how it gets warm at the fold.
If there is a heat gradient between the spacecraft and space. ie one is hot and the other cold, this heat energy will radiate from the spacecraft into space in the same way as it radiates from the bar of an electric fire. The rate of radiation is proportional to the square of the difference in temperatures, so a very hot body will begin cooling very quickly but the rate of cooling will reduce as the temperature difference reduces.
Having said all that....the thing would have to be shaking like a dance floor during an earthquake to produce appreciable amountsd of heat.
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That's my boy!
Could I just add to that that any body above absolute zero will radiate heat at a calculable rate, independent of its surroundings. The rate at which heat is radiated depends only on its absolute temperature and the properties of its outer surface. (i.e. it will still radiate heat even if it's the coldest thing around - it just means that it will absorb faster than it radiates until it reaches an equilibrium state).
[This message has been edited by Admiral James T. Kirk (edited 28 June 2001).]
Could I just add to that that any body above absolute zero will radiate heat at a calculable rate, independent of its surroundings. The rate at which heat is radiated depends only on its absolute temperature and the properties of its outer surface. (i.e. it will still radiate heat even if it's the coldest thing around - it just means that it will absorb faster than it radiates until it reaches an equilibrium state).
[This message has been edited by Admiral James T. Kirk (edited 28 June 2001).]
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But if you're in space there's nothing to radiate the heat to...
I understand the bar-heater analogy, but there's air present as the medium that transfers the heat.
Surely the heat would stay with the craft...?
Although it doesn't make sense to me that it would stay heated forever, so... how exactly does this heat transfer into nothing/space?
Geez I'm lovin' this!
I understand the bar-heater analogy, but there's air present as the medium that transfers the heat.
Surely the heat would stay with the craft...?
Although it doesn't make sense to me that it would stay heated forever, so... how exactly does this heat transfer into nothing/space?
Geez I'm lovin' this!
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Turbofan,
heat can be transferred in a number of ways. Convection (air), conduction or... yup, radiation in the EM spectrum. If heat could not be transferred throught empty space through radiation we wouldn't have much use of that sun thing, would we? *grin*
The heat isn't radiated TO anything per se, just radiated. The probabilities dictate that most likely it will hit something or other eventually, otherwise it will just continue forever, helping to expand our universe at the speed of light.
Now I'll go back to trying to figure out what a "quadripole source of noise" is. *grin* I'm impressed.
Cheers,
/ft
heat can be transferred in a number of ways. Convection (air), conduction or... yup, radiation in the EM spectrum. If heat could not be transferred throught empty space through radiation we wouldn't have much use of that sun thing, would we? *grin*
The heat isn't radiated TO anything per se, just radiated. The probabilities dictate that most likely it will hit something or other eventually, otherwise it will just continue forever, helping to expand our universe at the speed of light.
Now I'll go back to trying to figure out what a "quadripole source of noise" is. *grin* I'm impressed.
Cheers,
/ft
Guest
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Guest
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Look guys I only got a 3rd but this is really not that subtle.
Sound is simply a disturbance on the fluid medium in which the disturbance is generated. No medium; no sound.
Look at it this way. You descend over the Pacific gently. Everything is fine until you get to 0 amsl. Then the wings fall off.
Why?
Why didn't they fall off before?
Now reverse the argument. You create a sound in the dense medium known as air but as you climb to 3000000000 feet. No sound.
Actually of course Space is not a vacuum so there will be sound. It's just that it is so minimal you don't notice.
What about the engines vibrating? Well they will propagate sound through the vessel but it won't leave the vessel because the vibrations have no surrounding medium to vibrate. Does this mean anything? No. The damping effect of the air on the airframe is negligible by comparison.
Sound is simply a disturbance on the fluid medium in which the disturbance is generated. No medium; no sound.
Look at it this way. You descend over the Pacific gently. Everything is fine until you get to 0 amsl. Then the wings fall off.
Why?
Why didn't they fall off before?
Now reverse the argument. You create a sound in the dense medium known as air but as you climb to 3000000000 feet. No sound.
Actually of course Space is not a vacuum so there will be sound. It's just that it is so minimal you don't notice.
What about the engines vibrating? Well they will propagate sound through the vessel but it won't leave the vessel because the vibrations have no surrounding medium to vibrate. Does this mean anything? No. The damping effect of the air on the airframe is negligible by comparison.
Guest
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twisted,
in addition, above a certain altitude the air will start acting as separate particles rather than a fluid. I e sound waves will not propagate - no sound. They ran into this with some high altitude X series aircraft IIRC...
[Edit] Oh, and this of course meant that, for once, the "lift is created by air molecules bouncing off the bottom of the wing like marbles" finally got to be right. Once.
Nothing is ever simple! If it is, it ain't aviation!
Cheers,
/ft
[This message has been edited by ft (edited 30 June 2001).]
in addition, above a certain altitude the air will start acting as separate particles rather than a fluid. I e sound waves will not propagate - no sound. They ran into this with some high altitude X series aircraft IIRC...
[Edit] Oh, and this of course meant that, for once, the "lift is created by air molecules bouncing off the bottom of the wing like marbles" finally got to be right. Once.
Nothing is ever simple! If it is, it ain't aviation!
Cheers,
/ft
[This message has been edited by ft (edited 30 June 2001).]
Guest
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what what what is all this about..... Sound is simply, very simply brought about by changes in pressure. The rate at which you vary the pressure will determine the frequency of the sound you here. Sound waves are (on this earth) waves of changing air pressure. In space - no air - no sound.
However, when in space firing an engine, matter is diplaced from the engine. If you are behind this engine you will probably hear it. However the sound waves will be waves of the combustion products and not air.
Relevant??
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Doors to Automatic
However, when in space firing an engine, matter is diplaced from the engine. If you are behind this engine you will probably hear it. However the sound waves will be waves of the combustion products and not air.
Relevant??
------------------
Doors to Automatic