SPEED OF SOUND

[Jeanway 0]

COMPARE THE TWO. SOUNDS LIKE AN ESSAY QUESTION GO AHEAD:

[nik 0]

Velocity of either depends on the medium. However, in air at sea level:

 

Sound: 343 m/s

Light: 2.99*10^8 m/s

 

In water:

 

Light: 2.25*10^8 m/s

 

In NE-213 liquid scintillator (Xylene or tetrachloro-something or other):

1.998*10^8 m/s

 

A nice problem to do:

Determine the speed of light in a tube of water moving at 0.5c relative to a stationary observer.

[nik 0]

By the way, Jeanway, we're pretty sure that the speed of light is a great cosmic speed limit. Nothing moves faster.

what do you think happens when a particle moving at, say, 80% (0.8c) the speed of light in air enters water, in which the speed of light is only 75% the speed of light in air

(0.75c). Is the particle moving faster than the speed of light?

[Jeanway 0]

By the way, Jeanway, we're pretty sure that the speed of light is a great cosmic speed limit.  Nothing moves faster.

what do you think happens when a particle moving at, say, 80% (0.8c) the speed of light in air enters water, in which the speed of light is only 75% the speed of light in air

(0.75c).  Is the particle moving faster than the speed of light?

 

 

 

 

Your skirt flys up in your face :huh: Sorry nik, go on.

[Xeroc 0]

By the way, Jeanway, we're pretty sure that the speed of light is a great cosmic speed limit.  Nothing moves faster.

what do you think happens when a particle moving at, say, 80% (0.8c) the speed of light in air enters water, in which the speed of light is only 75% the speed of light in air

(0.75c).  Is the particle moving faster than the speed of light?

Actually nik, in water or any other substance for that matter the light doesn't actually slow down. What happens is that the light (photons) are aborbed and consequently reemitted by the electrons in the atoms of the substance, giving the illusion of the light slowing down. So light travels the same speed everywhere:

 

c = 299 792 458 m / s

c = 186 282.397 miles per second

[fenriz275 0]

By the way, Jeanway, we're pretty sure that the speed of light is a great cosmic speed limit.  Nothing moves faster.

what do you think happens when a particle moving at, say, 80% (0.8c) the speed of light in air enters water, in which the speed of light is only 75% the speed of light in air

(0.75c).  Is the particle moving faster than the speed of light?

I've read that tachyons travel faster than the speed of light and that they keep increasing speed as they lose mass. Is this true?

[Nemesis 0]

By the way, Jeanway, we're pretty sure that the speed of light is a great cosmic speed limit.  Nothing moves faster.

what do you think happens when a particle moving at, say, 80% (0.8c) the speed of light in air enters water, in which the speed of light is only 75% the speed of light in air

(0.75c).  Is the particle moving faster than the speed of light?

I've read that tachyons travel faster than the speed of light and that they keep increasing speed as they lose mass. Is this true?

They have not been proven to exist. I believe so..

[Jeanway 0]

.

.

.

UH OH, I'm In Trouble Deep Now <_< You've got formulas for all this, correct? PM them to me, I'll give it a try, no guarantees nik, it's been a while.

Edited April 22, 2004 by Alterego

[Xeroc 0]

By the way, Jeanway, we're pretty sure that the speed of light is a great cosmic speed limit.  Nothing moves faster.

what do you think happens when a particle moving at, say, 80% (0.8c) the speed of light in air enters water, in which the speed of light is only 75% the speed of light in air

(0.75c).  Is the particle moving faster than the speed of light?

I've read that tachyons travel faster than the speed of light and that they keep increasing speed as they lose mass. Is this true?

Tachyons are a theoretical particle derived from a mirror-image aspect of einstein's equations. They have never been detected so far.

 

They would operate in an oposite manner to normal matter so would gain mass as they slowed down to near the speed of light and would lose mass if they sped up. They would have to be created going faster than the speed of light and couldn't slow down below it.

[nik 0]

UH OH, I'm In Trouble Deep Now <_<  You've got formulas for all this, correct? PM them to me, I'll give it a try, no guarantees nik, it's been a while. 

Formulas? They're pretty involved, but doable none-the-less. They typically don't

teach the fundamentals of this stuff until grad school. (Derived formulas in college.)

However, it's always good to try. I can recommend introductory texts:

"Electicity and Magnetism" By Griffiths

for something a bit more involved, try: "Classical Electrodynamics" By J.D. Jackson.

(It's actually more than just classical.)

Edited April 22, 2004 by Alterego

[nik 0]

Actually nik, in water or any other substance for that matter the light doesn't actually slow down.  What happens is that the light (photons) are aborbed and consequently reemitted by the electrons in the atoms of the substance, giving the illusion of the light slowing down.  So light travels the same speed everywhere:

 

c = 299 792 458 m / s

c = 186 282.397 miles per second

True enough. So the answer is that if we have a particle that enters a medium at

a speed apparently faster than that of light in that medium, information transfer across that medium is limited to c/n. We see a phenomenon called Cerenkov radiation

(after a Russian). As the particle slows, light is emitted from the particle in a cone

called (what else?) a Cerenkov cone. I'm guessing that Ensign Jim Phaserman

has observed this effect, and maybe he'll tell you about it. However, it also occurs

in our atmospher. As cosmic rays enter the atmosphere, they will produce

what we call Cerenkov showers - huge cigar-shaped sources of light 100s of meters to

several km long in the atmospher. Typically very faint, but fascinating to observe with

extroardinarily large telescopes.

[Jeanway 0]

You trying to pull my leg? :P <_<

Edited April 22, 2004 by Jeanway

[nik 0]

No, not at all. This is real. Try googling the following:

Cerenkov (or Cherenkov, depending on the conversion from Cyrillic.) or Cerenkov radiation.

Whipple collaboration - I used to work for this group doing image analysis, cluster algorithms, and spline fits to data back in my undergrad days.

[Xeroc 0]

Yes, it is very real. Here is a link to a detailed explanation:

 

Cerenkov Radiation

[jefffitz 0]

David Byrne wrote "And She Was" about a friend of his who took LSD and contemplated a YOHOO factory. Therefore, physics doesn't enter into it.

 

The point of the Talking Heads song is that reality is elastic, "she" is both earthbound and airborn. If you've ever indulged (or in my case), studiously observed, on many occasions- the nature of psychedelia you know that all opposites are dissolved.

 

I hope this post answers more questions than it answers, asks, intimates, confuses, or confirms your question

[nik 0]

Yes, that is a fine explanation. The UPENN group does good work in that field. Fine work indeed. Thanks!

[nik 0]

David Byrne wrote "And She Was" about a friend of his who took LSD and contemplated a YOHOO factory.  Therefore, physics doesn't enter into it.

 

The point of the Talking Heads song is that reality is elastic, "she" is both earthbound and airborn.  If you've ever indulged (or in my case), studiously observed, on many occasions- the nature of psychedelia you know that all opposites are dissolved.

 

I hope this post answers more questions than it answers, asks, intimates, confuses, or confirms your question

Now I'm really confused!!!!!

 

However, going with the flow......

Did you see CNN's "Worst all time songs" list? Most of those were great songs.......

I don't get it?

[WEAREBORG4102 0]

don't confuse yourself, Buddy...

[Tench745 0]

True enough.  So the answer is that if we have a particle that enters a medium at

a speed apparently faster than that of light in that medium, information transfer across that medium is limited to c/n.

I'm sorry, this probably isn't a topic for the limited mind of a 16 year old, but I' like it. However, I can't remember what n is.

[WEAREBORG4102 0]

I'm only thirteen..

and I have a fusion idea...

go figure...

[nik 0]

True enough.  So the answer is that if we have a particle that enters a medium at

a speed apparently faster than that of light in that medium, information transfer across that medium is limited to c/n.

I'm sorry, this probably isn't a topic for the limited mind of a 16 year old, but I' like it. However, I can't remember what n is.

You're never to young to be inquisitive. The greatest physicist I've ever met were those with a youthful curiousity. My old sensei used to enjoy practical jokes becuase of his youthful nature.

 

n = the index of refraction of a medium. The ratio of cohent propagation of light in that medium to that in vacuo. On a fundamental level...... later.....

Did you know that some items have complex n (i.e. n= A + iB)?

[nik 0]

True enough.  So the answer is that if we have a particle that enters a medium at

a speed apparently faster than that of light in that medium, information transfer across that medium is limited to c/n.

I'm sorry, this probably isn't a topic for the limited mind of a 16 year old, but I' like it. However, I can't remember what n is.

You're never to young to be inquisitive. The greatest physicist I've ever met were those with a youthful curiousity. My old sensei used to enjoy practical jokes becuase of his youthful nature.

 

n = the index of refraction of a medium. The ratio of cohent propagation of light in that medium to that in vacuo. On a fundamental level...... later.....

Did you know that some items have complex n (i.e. n= A + iB)?

corretion: "....The ratio of cohent propagation velocity of light in vacuo to that of light (of the same frequency) in the medium for which n is defined. ..."

 

Note: n depends on frequency - a "dispersion relation"

[Jeanway 0]

David Byrne wrote "And She Was" about a friend of his who took LSD and contemplated a YOHOO factory.  Therefore, physics doesn't enter into it.

 

The point of the Talking Heads song is that reality is elastic, "she" is both earthbound and airborn.  If you've ever indulged (or in my case), studiously observed, on many occasions- the nature of psychedelia you know that all opposites are dissolved.

 

I hope this post answers more questions than it answers, asks, intimates, confuses, or confirms your question

 

 

 

 

 

Your talking about my Signature, you know B) Jefffitz :blink: