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(Harvard University)   If you think the idea of a reverse shock wave racing inward at Mach 1000 is counter intuitive, you aren't alone   (cfa.harvard.edu) divider line 30
    More: Strange, shock waves, supernova remnants, Center for Astrophysics, interstellar gas, Tycho Brahe, Tycho, Type Ia, ultimate fate  
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3665 clicks; posted to Geek » on 26 Nov 2013 at 7:19 AM (47 weeks ago)   |  Favorite    |   share:  Share on Twitter share via Email Share on Facebook   more»



30 Comments   (+0 »)
   
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2013-11-26 03:45:26 AM  
Mach 1000.  The inevitable Schick razor a few years from now.
 
ZAZ [TotalFark]
2013-11-26 07:40:14 AM  
I was about to be impressed until I decided they were misusing "mach" to mean "the speed of sound in air on Earth at sea level." Mach numbers should be quoted relative to local conditions.

Somebody less lazy could find a preprint and see if I'm right.
 
2013-11-26 07:52:42 AM  

RodneyToady: Mach 1000.  The inevitable Schick razor a few years from now.


Gillette. Come on, if you're gonna make a razor joke, get the brand right :P
 
2013-11-26 08:00:37 AM  
Is this 'reverse shockwave' in any way analogous to the effect that allows oil rig fires to be extinguished with dynamite?
 
2013-11-26 08:06:29 AM  

ZAZ: I was about to be impressed until I decided they were misusing "mach" to mean "the speed of sound in air on Earth at sea level." Mach numbers should be quoted relative to local conditions.

Somebody less lazy could find a preprint and see if I'm right.


So... mach infinity then? Since sounds doesn't travel at all in the vacuum of space?
 
2013-11-26 08:09:23 AM  
Mach 1000 isn't really all that fast on a galactic scale.  It is about what?  1/10th the speed of light.
 
2013-11-26 08:17:44 AM  

Muta: Mach 1000 isn't really all that fast on a galactic scale.  It is about what?  1/10th the speed of light.


~340 m/s for speed of sound and ~300,000,000 m/s for the speed of light, so about 1/1,000,000
 
ZAZ [TotalFark]
2013-11-26 08:21:17 AM  
Grither

Mach number is well defined under these circumstances. The gas is still gas even though it is thin. You can apply the compressible flow equations you learned in college for terrestrial use.

In astrophysical situations mach number sometimes becomes ill defined when the magnetic field is strong (magnetic pressure comparable to gas pressure). Then you have to use complicated equations and the ordinary shock rules don't apply any more.
 
2013-11-26 08:26:56 AM  

mutterfark: Is this 'reverse shockwave' in any way analogous to the effect that allows oil rig fires to be extinguished with dynamite?


Sure. Why not?

It's got to be a better analogy than "It's like the sea of brake lights as you approach a fender bender".
 
2013-11-26 08:29:37 AM  

somedude210: RodneyToady: Mach 1000.  The inevitable Schick razor a few years from now.

Gillette. Come on, if you're gonna make a razor joke, get the brand right :P


Stop maching him.
 
2013-11-26 08:33:43 AM  

grokca: somedude210: RodneyToady: Mach 1000.  The inevitable Schick razor a few years from now.

Gillette. Come on, if you're gonna make a razor joke, get the brand right :P

Stop maching him.


YOU'RE ALL MACHING ME CRAAAAAAZZZYYY
 
2013-11-26 08:38:32 AM  

MusicMakeMyHeadPound: mutterfark: Is this 'reverse shockwave' in any way analogous to the effect that allows oil rig fires to be extinguished with dynamite?

Sure. Why not?

It's got to be a better analogy than "It's like the sea of brake lights as you approach a fender bender".


That has to be the worst car analogy I've ever heard. Even with a background in aerodynamics I don't understand what they're trying to describe.
 
2013-11-26 08:52:38 AM  
Kind of like when you ride her up a little to close to the headboard.
 
2013-11-26 08:55:40 AM  
How does a shock wave propagating at one speed get reflected at > 3X that speed?  Doesn't that violate the law of conservation of momentum?
 
2013-11-26 09:13:24 AM  

AngryDragon: How does a shock wave propagating at one speed get reflected at > 3X that speed?  Doesn't that violate the law of conservation of momentum?


It's like those mirrors that make you look fat.
 
2013-11-26 09:15:09 AM  

Baryogenesis: Muta: Mach 1000 isn't really all that fast on a galactic scale.  It is about what?  1/10th the speed of light.

~340 m/s for speed of sound and ~300,000,000 m/s for the speed of light, so about 1/1,000,000


1/1,000,000 for Mach 1, not Mach 10000.

340,290 m2 / s2 compared to c would be ~1/880.
 
2013-11-26 09:15:44 AM  

Feepit: Mach 10000


Minus a 0. Mach 1,000.
 
2013-11-26 09:32:08 AM  

AngryDragon: How does a shock wave propagating at one speed get reflected at > 3X that speed?  Doesn't that violate the law of conservation of momentum?


FTA: The explosion spewed elements like silicon and iron into space at speeds of more than 11 million miles per hour (5,000 km/s).
When that ejecta rammed into surrounding interstellar gas, it created a shock wave - the equivalent of a cosmic "sonic boom." That shock wave continues to move outward today at about Mach 300. The interaction also created a violent "backwash" - a reverse shock wave that speeds inward at Mach 1000.


so, ejecta hits interstellar gas (at .0167 c) , creates 2 shockwaves, one inwards (.00113 c), one outwards (.00034 c) .

\\ pretty fascinating
\ it would be nice if science articles would keep their units coherent
 
2013-11-26 09:34:06 AM  

Feepit: Feepit: Mach 10000

Minus a 0. Mach 1,000.


That would've made you look real silly.  The difference is almost over 9,000.
 
2013-11-26 09:35:34 AM  

somedude210: grokca: somedude210: RodneyToady: Mach 1000.  The inevitable Schick razor a few years from now.

Gillette. Come on, if you're gonna make a razor joke, get the brand right :P

Stop maching him.

YOU'RE ALL MACHING ME CRAAAAAAZZZYYY


Fark everything, we're doing five blades.
 
2013-11-26 10:11:02 AM  

robertus: somedude210: grokca: somedude210: RodneyToady: Mach 1000.  The inevitable Schick razor a few years from now.

Gillette. Come on, if you're gonna make a razor joke, get the brand right :P

Stop maching him.

YOU'RE ALL MACHING ME CRAAAAAAZZZYYY

Fark everything, we're doing five blades.


20 is all we need

\\\\ four slashes when 3 isn't enough
 
2013-11-26 10:32:18 AM  
What a reverse shockwave may look like:

upload.wikimedia.org
 
2013-11-26 11:25:43 AM  

ZAZ: Grither

Mach number is well defined under these circumstances. The gas is still gas even though it is thin. You can apply the compressible flow equations you learned in college for terrestrial use.

In astrophysical situations mach number sometimes becomes ill defined when the magnetic field is strong (magnetic pressure comparable to gas pressure). Then you have to use complicated equations and the ordinary shock rules don't apply any more.


So why is this article using Mach? It seems like a very odd choice.
 
ZAZ [TotalFark]
2013-11-26 11:32:09 AM  
I found the paper (http://arxiv.org/abs/1310.8355). Turns out the use of Mach number is legitimate. The shocks are collisionless shocks, which are weird creatures that inhabit deep space.
 
2013-11-26 11:42:55 AM  

Chuck Wagon: So why is this article using Mach? It seems like a very odd choice.


Because it's one of the few speeds comprehensible to average people. When you get up to high velocities it just gets meaningless to people. However, even the scientifically unwashed understand that sound travels slower than light; one good thunderstorm will teach that. Hence the use of Mach numbers, even if they aren't all that usable in the context. People have an idea that Mach 1000 is really really fast. Giving it in relation to C would just cause eyes to glaze over.
 
2013-11-26 12:30:04 PM  

PanicMan: MusicMakeMyHeadPound: mutterfark: Is this 'reverse shockwave' in any way analogous to the effect that allows oil rig fires to be extinguished with dynamite?

Sure. Why not?

It's got to be a better analogy than "It's like the sea of brake lights as you approach a fender bender".

That has to be the worst car analogy I've ever heard. Even with a background in aerodynamics I don't understand what they're trying to describe.


Fry: Usually on the show, they came up with a complicated plan, then explained it with a simple analogy.
Leela: Hmmm... If we can re-route engine power through the primary weapons and configure them to Melllvar's frequency, that should overload his electro-quantum structure.
Bender: Like putting too much air in a balloon!
Fry: Of course! It's all so simple!
 
2013-11-26 12:52:05 PM  
So the analogy  "It's like the sea of brake lights as you approach a fender bender". works if you are someone observing the propagation of people applying their brakes due to the people ahead of them applying. The chain of people applying brakes is moving opposite relative to the direction the cars are travelling.
 
2013-11-26 01:05:06 PM  

MusicMakeMyHeadPound: mutterfark: Is this 'reverse shockwave' in any way analogous to the effect that allows oil rig fires to be extinguished with dynamite?

Sure. Why not?

It's got to be a better analogy than "It's like the sea of brake lights as you approach a fender bender".


Don't get me wrong, I realize that all the underlying mechanisms are completely different, I was just trying to visualize what they meant by a reverse shockwave.
 
2013-11-26 02:14:43 PM  
ZAZ

The shocks are collisionless shocks, which are weird creatures that inhabit deep space.

In deep space...abandoned.

Any crew?

Negative.
 
2013-11-26 09:46:38 PM  
according to Google calculator, the speed of light is Mach 880,991.09.
 
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