why does something become infinitely heavy as it approaches the speed of light? i can imagine 200,000mph and could even count that high given an hour or two (well sort of). so why can't something travel at that speed?
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stevew213 |
dumb questions from the perplexed..... maybe |
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how big can an aircraft get? which will ultimately limit it's ability to fly, airframe or engines? why?
why does something become infinitely heavy as it approaches the speed of light? i can imagine 200,000mph and could even count that high given an hour or two (well sort of). so why can't something travel at that speed? |
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bonedriver(d) |
Re: dumb questions from the perplexed..... maybe | ||
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Okay you asked for it now digest this!
www.phys.vt.edu/~jhs/faq/sr.html Same Below! Frequently Asked Questions About Special Relativity Compiled by Dr. John Simonetti of the Department of Physics at Virginia Tech. Back to Frequently Asked Astronomy and Physics Questions -------------------------------------------------------------------------------- Can you give me information on why travelling at light speed is so impossible? DS, 8th grade, Blacksburg Middle School, Blacksburg, Virginia, USA. 1996 Is there a chance that we may be able to go the speed of light sometime in the future? DS, 8th grade, Blacksburg Middle School, Blacksburg, Virginia, USA. 1996 Einstein said that if something could travel at light speed its mass would duplicate. How could it be? JLR, UAM, Mexico City, Mexico. 1997 Please explain how the Twin Paradox works. 1997 -------------------------------------------------------------------------------- Can you give me information on why travelling at light speed is so impossible? Einstein's Special Theory of Relativity is the key to understanding this particular question. Any reference on the subject (and I'm sure there are loads of them written for a wide range of students) will have some discussion on this. Briefly, to make an object accelerate from rest to any speed, we must expend some energy (by using a rocket engine, say). For low speeds (much less than the speed of light --- 186,000 miles per second; all all humans have traveled only at very slow speeds compared to that of light), an increase in the energy expended results in a reasonable increase in the speed of the object. However, as the SR theory says, when the object is traveling at very large speeds (= a considerable fraction of the speed of light), then an additional expenditure of energy will not result in as large an increase in speed as it would have at lower speeds. In other words, we have to expend quite a bit of energy to increase the speed by only a little bit, if the rocket ship is already traveling fast. If the rocket ship is traveling at 95% of the speed of light, a trememdous amount of energy will be necessary to make it travel at 96% the speed of light. In trying to make it travel at the speed of light, we would need to expend an infinite amount of energy --- in other words, we can't make it travel at the speed of light. Now, every space ship, or other plane, etc., has traveled at a speed very small compared to light, so you might be wondering how we know the Special Relativity Theory is correct (why should we believe it without evidence?). Although, we have never made any large object (like a space ship) travel at a considerable fraction of light speed, experimental particle physicists are constantly making electrons and the like travel at speeds like 99% of the speed of light in particle accelerators. These accelerators only work properly because they are constructed obeying the laws of Special Relativity. To make the electrons accelerate, when they are already at 90% of the speed of light, does indeed take quite a bit more energy than would a comparable speed change when they are only moving at 10% of the speed of light. Special Relativity theory appears correct, in detail, even under the extreme speed conditions of a particle accelerator. Is there a chance that we may be able to go the speed of light sometime in the future? Since Special Relativity theory appears correct even under the extreme speed conditions of a particle accelerator, it is unlikely we will ever find a way to travel through space at a speed greater than (or even equal to) the speed of light. However, if your goal is to get from one place to another distant place in a time less than it would take to get there by normal space travel (at a speed less than light), there may be some way to get from one place to another without traveling "through the intervening space", by going through some sort of wormhole or other tunnel, but at the moment such ideas are nearly entirely speculative --- any progress in such a possiblility (if it's even possible), would have to occur in the future. But people are looking into it. An interesting reference on that would be Kip Thorne's book "Black Holes and Time Warps" which was published last year (I think). Einstein said that if something could travel at light speed its mass would duplicate. How could it be? Actually, here's the way it should be said: energy and mass are related. If you set up a "black box" (box you can't see into) containing some atoms, the total mass of the box and its contents will be equal to the sum of the mass of the box and mass of the individual atoms in the box. If you heat the box to a high temperature (so the atoms are moving around at high speed in the box, and thus have high energy), then the total mass of the box and its contents will be larger than if the temperature of the box is lower. Why? Because, the higher energy atoms contribute more mass to the total mass than before the box was heated. So, if you try to push on the box, you will discover that its inertia will be larger (it won't accelerate as quickly). In a practical setup of this box containing gas, the actual change in inertia of the box (due to heating it) will be small. But, in principle, if the atoms are made to move at speeds nearing the speed of light, the mass of the box can be made very large --- even approaching infinity. |
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Toby |
Re: dumb questions from the perplexed..... maybe | ||
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Steve,
How big can an aircraft get? Limited by the length of runways and the airport infrastructure more than by technology I suspect. What limits engines? Turbine Entry Temperature - the gases flowing out of the combustion chamber in the engine are so hot their temperature cannot be measured, only calculated using the isentropic relations and knowing the pressure drop across the turbine(s). Already we have turbine cooling down to such a fine art we can have the gases entering a 400deg C above their melting temperature. Another limitation is on the size of fans, compressors and turbines, you dont want the tip speeds to be [significantly?] supersonic. Therefore the bigger the diameter of these devices the slower they can be allowed to rotate. Additional limitations that I could see on size are: ability to manufacture such an aircraft, finding a suitable power plant and public acceptance of an aerial "Titanic". why does something become infinitely heavy as it approaches the speed of light? 'Cause Mr Einstein said so |
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stevew213 |
Re: dumb questions from the perplexed..... maybe | ||
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'Another limitation is on the size of fans, compressors and turbines, you dont want the tip speeds to be [significantly?] supersonic. Therefore the bigger the diameter of these devices the slower they can be allowed to rotate.'
this is what really prompted the question. there must be a point where speed of fans, compression ratios, temperatures, exhaust velocities render the jet engine ineffective: a theoretical maximum? other than material limits for airframes use, i hadn't thought about the others as to the mass getting greater due to heating effects.... i shall have to do a before and after experiment weighing my kettle then |
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1995hoo |
Re: dumb questions from the perplexed..... maybe | ||
Quote:Given that he is from Virginia Tech (and how I SHUDDER to use "Virginia" in the name of that institution), we must question everything he says unless he is talking about cross-breeding sheep with human beings!!!! Proof is that those kids asked about travelling at light-speed. A REAL resident of Blacksburg would ask whether going that fast would allow him to outrun the smell of cow manure that permeates Blacksburg!!! (For those who go "huh," that logo under my name represents the University of Virginia and we have a rather heated rivalry with VT.) |
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funkymonkey |
Re: dumb questions from the perplexed..... maybe | ||
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steve, agreed, there is a theoretical maximum for conventional twin-spool turbines, whch was met when designing the trent 900's for the A380. To overcome this, they introduced a triple-spool system, allowing the high conpression blabes to run at much higher speeds than the 1st stage spool. I hope this helps a little
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bonedriver(d) |
Re: dumb questions from the perplexed..... maybe | ||
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Worlds Biggest wooden Flying Machine!
www.sprucegoose.org/ homepages.tesco.net/~paul.crossley/goose.htm |
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bonedriver(d) |
Re: dumb questions from the perplexed..... maybe | ||
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Toby |
Re: dumb questions from the perplexed..... maybe | ||
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Funkymonkey - ALL RB211s right back to the -22B on the Tristar are triple spool. The reason is to allow more of the compressor stages to operate "on design" and alleviate problems such as "windmilling" at low speed.
They also claim this allows the engine to be more compact than twin spool designs. There is a direct relationship between compressor pressure ratio and efficiency, though it appears that above OPRs of ~50, no further gain is made. |
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funkymonkey |
Re: dumb questions from the perplexed..... maybe | ||
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toby, as always your knowledge far outweighs mine, thanks for the info.
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Toby |
Re: dumb questions from the perplexed..... maybe | ||
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Might interest you to know that G-AVMN is going to Denmark (in kit form) to become a restaurant.
I should have also pointed out in my last post, that the GE90 and the similar size P&W engine are still twin spool. There are pros and cons for both designs. |
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bonedriver(d) |
Re: dumb questions from the perplexed..... maybe | ||
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The GE90 Engine!
www.grc.nasa.gov/WWW/RT1998/2000/2900veres.html Also loads of Engine links! www.esparacing.com/sport%20pilot/links%20listing/26.htm |
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