ChrisButler
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| posted on 19/5/06 at 05:39 PM |
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No, not the speed of light: the speed of sound in the metal (much faster than the speed of sound in air, but much slower than the speed of light).
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DIY Si
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| posted on 19/5/06 at 05:45 PM |
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Easiest way to look at it is as a compression wave going down the pipe. It'll travel just as a sound wave would in air. Ie at the speed of
sound, which will be much, much higher than it is in air.
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JoelP
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| posted on 19/5/06 at 05:51 PM |
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you could probably make it exceed the speed of sound of a given material if you forced it, with similar effects to a sonic boom.  Would be
interesting to see anyway.
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DIY Si
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| posted on 19/5/06 at 05:58 PM |
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Not sure how you'd get it to go that fast. You'd need a very rapidly moving piston to exceed the speed of sound in the fluid. And what
would happen inside the pipe? Or would the pipe just rupture due to the huge force?
Just as a thought, could you fire something at a very high speed into/through a tank of the fluid to get the effect? But how would you fire something
at such a high speed? Probably looking at 5~10+ times the speed of sound in air?
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cossey
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| posted on 19/5/06 at 06:17 PM |
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1stly you probably couldnt get the piston to go fast enough it would have to go over 1200m/s which is about 2700mph to break the speed of sound.
2ndly most m/cs the output is smaller than the piston so the fluid would go faster through the connection until it hit mach 1 then the connection
would become a chocked nozzle and the pressure would just increase so that the piston couldnt go any faster. the piston would be doing a few hundred
mph though. all assuming it didnt blow itself apart.
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MikeR
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| posted on 19/5/06 at 06:26 PM |
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but, assuming your housing was strong enough and you could force the piston fast enough ..........
could it be done? To me it seems, obvious, yes. Just needs an incredibly fast strong piston.
now will someone interject with the correct physics to explain why i'm talking out of my arse as usual
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JoelP
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| posted on 19/5/06 at 06:37 PM |
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easier to imagine knocking the steel bar rather than the brake fluids, then you can ignore fluid dynamics and stuff. So assuming you accelerated a
mass in a vacuum, maybe by electromagnetism, and smashed it into a long steel bar, its easy to imagine what would happen! The bar would crumple up,
hence proving that you cant send a signal up a bar of steel faster than the speed of wave propigation in steel.
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Tom Beattie
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| posted on 19/5/06 at 06:55 PM |
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Fascinating, so if you are travelling at the speed of light and look over your shoulder I presume you see nothing?.
According to the saying "you can't find where you're going til you know where you've been" so you'll be lost, like
me reading this thread. And I thought the suspension geometry was hard!!!!
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DIY Si
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| posted on 19/5/06 at 07:07 PM |
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You would see backwards at just below the speed of light. The trick is remebering that time slows down as you approach the speed of light. So as you
approach the speed of light, light still ctaches you up, but very slowly. However, since time has slowed it would appear as normal. At the speed of
light, time should stand still, so you wouldn't be able to turn you're head round!
[Edited on 19/5/06 by DIY Si]
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Tom Beattie
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| posted on 19/5/06 at 07:39 PM |
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My head is spinning at the speed of light!!!!!!
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Simon
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| posted on 19/5/06 at 07:55 PM |
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Ok,
If nothing can exceed the speed of light, and given that black holes have such huge gravitational forces that light cannot escape (hence the name),
surely gravity itself is exceeding the speed of light.
ATB
Simon
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DIY Si
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| posted on 19/5/06 at 08:05 PM |
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It's not that gravity is reaching out to the light (and therefore going faster) it's that the light, being a wave-particle is drwan to the
source of gravity. Light for example will "bend" round planets, so it's possable to see something behind the planet. Assuming
it's a fair way off mind. Hence, balck holes have such a huge gravitational attraction that they bend the light so much it curves in towards the
balck hole in a spiral which ends at the black hole itself. Whatever that is.
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MikeR
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| posted on 19/5/06 at 11:02 PM |
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but i will now refer you to my previous statement. We have proved on this planet the speed of light varies. Gravity affects it and can slow or speed
it up (a very tiny amount).
SO, if the speed of light isn't constent how can some particles exceed when compared to somewhere else. Doesn't make sense to me.
But i'm soooo far out of my depth i've come out the other side!
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C10CoryM
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| posted on 20/5/06 at 03:37 AM |
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Theory of relativity doesn't say that nothing can go faster than the speed of light. It only restricts information and any information carrier
from going faster than light speed. I think the best example I've heard is of a powerful laser aimed millions of miles away into space. The
end of the laser beam would be moving over the speed of light if you started waving the laser around frantically.
Also, speed of light is definitely NOT constant. People have slowed, stopped and restarted light. Its called "slow light". Also do a
search for "Fast light" too  . It just seems wrong to me that things would drastically change at the speed of light. People thought
planes would explode at the speed of sound too.
FYI I have nfc what I am talking about. Just trivia I have picked up over the years. I forget who said it, but I like this quote:
"Why do people argue about how many stars there are? Because they will never be proven wrong!"
Applies to the whole light speed thing I think .
Cheers.
"Our watchword evermore shall be: The Maple Leaf Forever!"
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jollygreengiant
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| posted on 20/5/06 at 10:00 AM |
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quote:
Originally posted by Liam
quote:
Originally posted by JoelP
neither energy, information or matter can exceed the speed of light. If you get a metal bar 2 miles long, when you whack one end the other end will
not move instantly, a ripple of compression will move (very fast) to the other end, but the speed of light will never be breached. The same as
hydraulic fluid, it doesnt noticably compress but in fact, it does fractionally.
Guess you're right of course. Just that i was thinking more along the lines of a metal rod extending to about the sun. Pull on one end and
it'd take 8 minutes for the other end to move. Well yeah i guess it would. How interesting. (and that's ignoring pedantic details like
the fact i would struggle to overcome the billions of tonnes of inertia of my metal rod and pull it at all, etc etc etc)
Liam
Ah but you couldn't have a metal rod from the sun to us. Firstly the suns temperature is to high and the rod would melt as soon as it got within
a few thousand miles of the sun. Secondly the sun exerts a far greater gravitational pull so a soon as the rod got near to the sun then a chain
reaction would occur that would pull the rod into the sun (melting asside), so you would need to continually supply metal rod from this end and we
would eventually run out of supplies of metal rod, or, you would need to exert a strong clamping force at this end which would result in two effects.
Either the Earth would be pulled toward the sun by the metal rod OR when you eventually found a thermal protection suit and got to the end of the rod
to hit it with a hammer (IF you could withstand the gravitational forces AND the heat) you would eventually knock the Earth out of orbit when the
strike manifested its self down the bar, IF the forces of the strike were not cancelled out by other celestial forces that we have not thought of
explaining away with all this theorising.
Enjoy
[Edited on 20/5/06 by jollygreengiant]
Beware of the Goldfish in the tulip mines. The ONLY defence against them is smoking peanut butter sandwiches.
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MikeR
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| posted on 20/5/06 at 11:17 AM |
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Some people just don't know how to have a theoretical conversation and try to spoil it with there bully fact boy tatics!
humph, i'm sulking now!
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DIY Si
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| posted on 20/5/06 at 08:23 PM |
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quote:
I think the best example I've heard is of a powerful laser aimed millions of miles away into space. The end of the laser beam would be moving
over the speed of light if you started waving the laser around frantically
Sorry, but that's wrong. The end of the laser beam is moving forwards at the speed of light and so as you move it side ways the light leaving
the laser at that time has just been pointed somewhere else. Only that light moves, not the entire beam. It's not solid remember. And even if it
were it would still move with the speed of the compression wave down it, as one particle has to exert a force on the adjacent one, and so on, down the
bar to make it move.
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C10CoryM
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| posted on 20/5/06 at 09:42 PM |
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quote:
Originally posted by DIY Si
quote:
I think the best example I've heard is of a powerful laser aimed millions of miles away into space. The end of the laser beam would be moving
over the speed of light if you started waving the laser around frantically
Sorry, but that's wrong. The end of the laser beam is moving forwards at the speed of light and so as you move it side ways the light leaving
the laser at that time has just been pointed somewhere else. Only that light moves, not the entire beam. It's not solid remember. And even if it
were it would still move with the speed of the compression wave down it, as one particle has to exert a force on the adjacent one, and so on, down the
bar to make it move.
Well it is mostly right, but only if you explain it better than I did last night (lazy).
Shine a visible laser at a far away planet at point A and quickly move it to point B. The visible dot will move from A-B faster than a laser at A
can emit light to B. It doesn't affect relativity because the dot is not capable of sending information, or moving any matter. The dot is
mearly a coordinate.
I think thats right. If not read the attached links. Im sure they are much smarter than me. Relativity is not a area interest to me so I
don't think about it often (or well ). Some of the paradoxes are neat though.
Cheers.
Info
http://www.physlink.com/education/askexperts/ae497.cfm
http://members.tripod.com/conduit9SR/SR11.html
http://www.antonine-education.co.uk/Physics_A2/Options/Module_8/Topic_6/answer_8_6_8.htm
http://www.phy.duke.edu/research/photon/qelectron/proj/infv/fast_tut.ptml
"Our watchword evermore shall be: The Maple Leaf Forever!"
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JoelP
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| posted on 20/5/06 at 10:41 PM |
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theres several reasons why thats all wrong unfortunately, but i cant be arsed to go into it. Too late in the day 
but i get what you mean, the dot can move faster than light because it isnt a continous entity.
[Edited on 20/5/06 by JoelP]
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DIY Si
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| posted on 20/5/06 at 11:17 PM |
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Nope, still not true. The dot only appears once the newly aimed leaser has emmited light in that direction and it's arrived at that point. If
you want to look at it from an info carrying point of view, a laser IS an info carrying/emitting device. Just ask any tele comms techy. The dot can
not appear at the new point until the light has arrived, so it can't travel faster than the light making the dot.
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MikeR
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| posted on 21/5/06 at 01:00 AM |
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For one i agree with someone - that makes perfect sense to me (but then again i like to think of myself as a techy )
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JoelP
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| posted on 21/5/06 at 10:30 AM |
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quote:
Originally posted by DIY Si
Nope, still not true. The dot only appears once the newly aimed leaser has emmited light in that direction and it's arrived at that point. If
you want to look at it from an info carrying point of view, a laser IS an info carrying/emitting device. Just ask any tele comms techy. The dot can
not appear at the new point until the light has arrived, so it can't travel faster than the light making the dot.
look at it like this. You point a laser one way, lets say it shows up on a wall 100 light years away. You wiggle it, the dot moves. If you suddenly
turn it by 180 degrees and point it at another wall, again 100 light years away, the dot would appear there 100 years later, and the dot would also
still be on the first wall 100 years later, so the dot would appear to have moved 200 light years in no time at all. How to explain this? Does the dot
move in jumps? Does it disappear and reappear? No, it would just move. And in this case, i fail to see how any information could be sent from one wall
to the other. Modifying the dot at the first wall wouldnt allow info to be sent to the second wall because the dot is being constantly refreshed from
the source, hence it can only be changed from here.
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MikeR
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| posted on 21/5/06 at 10:50 AM |
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Imagine firing a water cannon at a wall 100m away.
The water is leaving the cannon at 50m/s. So it takes 2 seconds for the water to get to the wall.
You flip the cannon round to a wall 180 degrees away in less than a second. You leave a curved trail of water as you do the move, its not a straight
line moving round because you're moving so quickly.
The shape of the curve will depend on how quickly you move the cannon. Really quickly and the curve will all be at the cannon nozzel. Really slowly
and the curve will be 100m out.
the same is true of light the light, i've just used a different medium.
(folks, i know i've simplied a lot of physics there, but that works out in my head so PLEASE don't tell me i'm wrong).
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DIY Si
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| posted on 21/5/06 at 10:53 AM |
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The point is, the dot isn't a fixed entity (for want of a better word) All the dot is is this emitted light. It isn't a thing in
it's own right, it's merely the light running into something and reflecting. Also as you wiggle the laser, the dot would take 100 years to
follow your wiggles. (I think you already know this, but for any reading that didn't...) So, going on your thinking, yes the dot may appear to
travel 200 light years, but it's a totally different dot caused by totally different photons hitting a different wall. And I may be wrong about
this, but I thought light always carried information due to it being a discrete wavelength. Ie if nothing else it carries that info around. Could be
wrong on that bit though.
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JoelP
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| posted on 21/5/06 at 10:54 AM |
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assuming the wall goes all the way round, 100m away, then the 'splodge' would move 314m in one second.
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