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Red_Dragon

Red_Dragon Avatar

Location: Dumbf*ckistan


Posted: May 30, 2011 - 7:42pm

 helenofjoy wrote:
This made my face hurt.

 
yes.
jadewahoo

jadewahoo Avatar

Location: Puerto Viejo, Costa Rica
Gender: Male


Posted: May 30, 2011 - 6:55pm

 beamends wrote:

Or coffee.
 
{#Roflol}

beamends

beamends Avatar



Posted: May 30, 2011 - 3:26pm

 oldslabsides wrote:

I bet this makes a wave, too

 

 
Or coffee.

Lazy8

Lazy8 Avatar

Location: The Gallatin Valley of Montana
Gender: Male


Posted: May 30, 2011 - 3:23pm

 helenofjoy wrote:
This made my face hurt.

I forgot to mention: point the knife away from your face!

helenofjoy

helenofjoy Avatar

Location: Lincoln, Nebraska
Gender: Female


Posted: May 30, 2011 - 3:22pm

 Lazy8 wrote:
 oldslabsides wrote:
now wait a minute...

What if this were filmed from above the trombone?  Or from beneath; would the "shockwave" still be in the shape of an arc?  Something about the perspective here just doesn't seem real to me.

Yes. Shockwaves are a finite thickness, and what you see is the light bending as it passes thru the shockwave. From the side the light passes thru more of the shockwave along the leading surface of the shock than is does behind the leading surface on its way to you, so you see it in profile.

Here's a way to think about it that might help: hold an imaginary half of a pumpkin in your hand with the guts all scooped out. It's a pretty much a uniform thickness. Now imagine you have a long pumpkin-carving knife you can poke thru the pumpkin, and poke it thru near the open end of the pumpkin, all the way across.

It goes thru nearly perpendicular to the outer surface, which penetrates nearly the minimum amount of pumpkin possible while still getting thru both sides. Now poke it thru sideways across the bottom of the pumpkin. Since it goes thru the wall at a shallower angle it goes thru more pumpkin on its way out the other side. Poke it thru low enough and its whole trip thru will be inside the wall of the pumpkin. A ray of light taking that path will see the maximum amount of distortion from the differential index of refraction of the shock wave—not because it spent more time in the different index, but because it had farther to go before its path straightened out again when it reached undisturbed air on the other side.

So rays of light along the leading surface of the shock will appear to show it in cross-section.
  This made my face hurt.


Lazy8

Lazy8 Avatar

Location: The Gallatin Valley of Montana
Gender: Male


Posted: May 30, 2011 - 3:16pm

 oldslabsides wrote:
now wait a minute...

What if this were filmed from above the trombone?  Or from beneath; would the "shockwave" still be in the shape of an arc?  Something about the perspective here just doesn't seem real to me.

Yes. Shockwaves are a finite thickness, and what you see is the light bending as it passes thru the shockwave. From the side the light passes thru more of the shockwave along the leading surface of the shock than is does behind the leading surface on its way to you, so you see it in profile.

Here's a way to think about it that might help: hold an imaginary half of a pumpkin in your hand with the guts all scooped out. It's a pretty much a uniform thickness. Now imagine you have a long pumpkin-carving knife you can poke thru the pumpkin, and poke it thru near the open end of the pumpkin, all the way across.

It goes thru nearly perpendicular to the outer surface, which penetrates nearly the minimum amount of pumpkin possible while still getting thru both sides. Now poke it thru sideways across the bottom of the pumpkin. Since it goes thru the wall at a shallower angle it goes thru more pumpkin on its way out the other side. Poke it thru low enough and its whole trip thru will be inside the wall of the pumpkin. A ray of light taking that path will see the maximum amount of distortion from the differential index of refraction of the shock wave—not because it spent more time in the different index, but because it had farther to go before its path straightened out again when it reached undisturbed air on the other side.

So rays of light along the leading surface of the shock will appear to show it in cross-section.

Red_Dragon

Red_Dragon Avatar

Location: Dumbf*ckistan


Posted: May 30, 2011 - 8:13am

 ptooey wrote:

We're a little short on brass instruments, actually.  I've got 2 guitars, a drum set, a piano, and a harmonica (oh, and I'm expecting a ukulele on Thursday .)  The kids have an accordion and a cello. 
 
I bet this makes a wave, too

 
ptooey

ptooey Avatar

Location: right behind you. no, over there.
Gender: Male


Posted: May 30, 2011 - 8:05am

 NoEnzLefttoSplit wrote:


Yeah, but what about the trombone?

 
We're a little short on brass instruments, actually.  I've got 2 guitars, a drum set, a piano, and a harmonica (oh, and I'm expecting a ukulele on Thursday .)  The kids have an accordion and a cello. 

NoEnzLefttoSplit

NoEnzLefttoSplit Avatar

Gender: Male


Posted: May 30, 2011 - 8:02am

 ptooey wrote:

Yeah, I've got a couple of old scientific surplus catalogs sitting at the house.  I'll check into what they've got.  It really doesn't look all that tough.
 

Yeah, but what about the trombone?
ptooey

ptooey Avatar

Location: right behind you. no, over there.
Gender: Male


Posted: May 30, 2011 - 7:58am

 ScottFromWyoming wrote:

I thought that might be trouble
 
$250 is the price for new. Talk to someone there about what you need: a mirror out of a trashed telescope, it can have some scratches, I doubt that will matter much. 

 
Yeah, I've got a couple of old scientific surplus catalogs sitting at the house.  I'll check into what they've got.  It really doesn't look all that tough.

ScottFromWyoming

ScottFromWyoming Avatar

Location: Powell
Gender: Male


Posted: May 30, 2011 - 7:56am

 ptooey wrote:

Dammit.  Dammit, dammit, dammit. 

*heads off to e-bay*

Edit:  $250 for an 8" mirror.  Ahh.  Nope.
 
I thought that might be trouble
 
$250 is the price for new. Talk to someone there about what you need: a mirror out of a trashed telescope, it can have some scratches, I doubt that will matter much. 
Red_Dragon

Red_Dragon Avatar

Location: Dumbf*ckistan


Posted: May 30, 2011 - 7:47am

 ptooey wrote:

Dammit.  Dammit, dammit, dammit. 

*heads off to e-bay*
 

ptooey

ptooey Avatar

Location: right behind you. no, over there.
Gender: Male


Posted: May 30, 2011 - 7:44am

 ScottFromWyoming wrote: 
Dammit.  Dammit, dammit, dammit. 

*heads off to e-bay*

Edit:  $250 for an 8" mirror.  Ahh.  Nope.

ScottFromWyoming

ScottFromWyoming Avatar

Location: Powell
Gender: Male


Posted: May 30, 2011 - 7:27am

 oldslabsides wrote:
now wait a minute...

What if this were filmed from above the trombone?  Or from beneath; would the "shockwave" still be in the shape of an arc?  Something about the perspective here just doesn't seem real to me. 
 
The depth of field is so shallow that it essentially is showing you just a cross-section of the half-a-bubble wave. Nearer to or further from the lens is out of focus so it doesn't show up.

Edit: well I was on the right track crack.

Schleiren photography note the link from there to Collimated light

A do-it-yourself guide to Schlieren photography 


NoEnzLefttoSplit

NoEnzLefttoSplit Avatar

Gender: Male


Posted: May 30, 2011 - 6:47am

 oldslabsides wrote:
now wait a minute...

What if this were filmed from above the trombone?  Or from beneath; would the "shockwave" still be in the shape of an arc?  Something about the perspective here just doesn't seem real to me. 

 

i think its because the wave will travel slower as it propagates out to the sides, kind of like waves turning the corner at the beach, presuming you have a beach with corners, that is..
oldviolin

oldviolin Avatar

Location: esse quam videri
Gender: Male


Posted: May 30, 2011 - 6:41am

 oldslabsides wrote:

yes, but the contact lens has an edge in addition to its convex side...

who said anythin' about hatin'? 

 

But I see the edge. Don't you?
just rattling your cage...
Red_Dragon

Red_Dragon Avatar

Location: Dumbf*ckistan


Posted: May 30, 2011 - 6:36am

 oldviolin wrote:


look at a contact lens from the side...any side, and it's the same. The shock wave is basicallythe same convex shape. maybe...
stop hatin' on peoples horn bones will ya?
 
yes, but the contact lens has an edge in addition to its convex side...

who said anythin' about hatin'? 
beamends

beamends Avatar



Posted: May 30, 2011 - 6:35am

 oldviolin wrote:


look at a contact lens from the side...any side, and it's the same. The shock wave is basicallythe same convex shape. maybe...
stop hatin' on peoples horn bones will ya?


 
or the shock wave from an explosion, wherever you view from it's still dome shaped (in ideal conditions).

oldviolin

oldviolin Avatar

Location: esse quam videri
Gender: Male


Posted: May 30, 2011 - 6:32am

 oldslabsides wrote:
now wait a minute...

What if this were filmed from above the trombone?  Or from beneath; would the "shockwave" still be in the shape of an arc?  Something about the perspective here just doesn't seem real to me. 

 

look at a contact lens from the side...any side, and it's the same. The shock wave is basicallythe same convex shape. maybe...
stop hatin' on peoples horn bones will ya?

Red_Dragon

Red_Dragon Avatar

Location: Dumbf*ckistan


Posted: May 30, 2011 - 6:19am

now wait a minute...

What if this were filmed from above the trombone?  Or from beneath; would the "shockwave" still be in the shape of an arc?  Something about the perspective here just doesn't seem real to me. 
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