bercov@bevsun.bev.lbl.gov (John Bercovitz) (06/13/91)
The speed of sound is referred to fairly often in this newsgroup and
occasionally there are quantification errors. If we ever start a FAQ,
the following might be useful.
The speed of sound in air is (kgRT)^0.5. Notice that the only variable
is T. So the velocity of sound doesn't depend on its pressure. Subbing
in values for k,g,and R with degrees Rankine for an input and feet per
second for an output: c = 49*(T)^0.5 to about four significant places.
Rem: To get to degrees Rankine, add 460 to degrees F.
Example: t = 68F so T = 528R
c = 49*(528)^0.5 = 1126 fps
Another thought mentioned in this group at times is that a supersonic
bullet causes shock waves when it enters a semi-liquid medium. It's
certainly true that anything traveling faster than the speed of sound
in a medium has shock waves coming off of it. But the speed of sound
in water is around 5000 fps. A critter with a projectile traversing
his carcass is going to experience traumatic shock but not shock waves.
Perhaps that's the source of the confusion 'mongst the gun rag writers.
Nitpicking: It is possible to get some very small local shock waves
at the front of a flat-nosed bullet if it is only slightly subsonic
in the traversed medium.
If you must create shock waves in a critter, you're not going to be
able to do it with a conventional firearm which, due to propellant
limitations, has a maximum projectile velocity of around 4500 fps.
Instead, you'll have to step up to a gas gun at least.
The speed of sound in solids is higher yet. Lead is not very stiff
but it is quite dense so the speed of sound in it is around 6400 fps.
At the other end of the spectrum, beryllium is quite stiff but has a
low density. The speed of sound in it is around 42,000 fps. Steel
and copper lie in between at 19,000 and 16,000 fps respectively.
JHBercovitz@lbl.gov (John Bercovitz)gary@gatech.edu (Gary Coffman) (06/15/91)
In article <35545@mimsy.umd.edu> bercov@bevsun.bev.lbl.gov (John Bercovitz) writes:
#
#Another thought mentioned in this group at times is that a supersonic
#bullet causes shock waves when it enters a semi-liquid medium. It's
#certainly true that anything traveling faster than the speed of sound
#in a medium has shock waves coming off of it. But the speed of sound
#in water is around 5000 fps. A critter with a projectile traversing
#his carcass is going to experience traumatic shock but not shock waves.
#Perhaps that's the source of the confusion 'mongst the gun rag writers.
#Nitpicking: It is possible to get some very small local shock waves
#at the front of a flat-nosed bullet if it is only slightly subsonic
#in the traversed medium.
I believe you, but I've seen high speed shadowgraphs of bullets that
had what definitely looked like shock waves trailing from the nose.
I've also seen boats moving considerably slower than 5000 fps with
the same sort of "bow wake" as the bullet had. I've dressed enough
game to know that *something* damages a conical section of meat
surrounding the wound channel. So if this isn't a sonic boom style
shock wave, what is it?
Garybercov@bevsun.bev.lbl.gov (John Bercovitz) (06/15/91)
#In article <35658@mimsy.umd.edu> ke4zv!gary@gatech.edu (Gary Coffman) writes: ##In article <35545@mimsy.umd.edu> bercov@bevsun.bev.lbl.gov ##(John Bercovitz) writes: ##Another thought mentioned in this group at times is that a supersonic ##bullet causes shock waves when it enters a semi-liquid medium. It's ##certainly true that anything traveling faster than the speed of sound ##in a medium has shock waves coming off of it. But the speed of sound ##in water is around 5000 fps. A critter with a projectile traversing ##his carcass is going to experience traumatic shock but not shock waves. ##Perhaps that's the source of the confusion 'mongst the gun rag writers. ##Nitpicking: It is possible to get some very small local shock waves ##at the front of a flat-nosed bullet if it is only slightly subsonic ##in the traversed medium. #I believe you, but I've seen high speed shadowgraphs of bullets that #had what definitely looked like shock waves trailing from the nose. Those bullets were supersonic because they were traveling through air which, of course, has a lower speed of sound. #I've also seen boats moving considerably slower than 5000 fps with #the same sort of "bow wake" as the bullet had. That's a different phenomenon but there's some amazing similitude there, huh? There's a reason for that. Maybe someone can tell us what it is. #I've dressed enough game to know that *something* damages a #conical section of meat surrounding the wound channel. #So if this isn't a sonic boom style shock wave, what is it? I see a bullet traversing the euphemism as primarily a momentum transfer problem. This is because the forces involved in the momentum transfer are much higher than the forces involved in destroying the structural integrity of the euphemism. So I would say the wound channel is the result of all the little dMs (that's dee masses) becoming sub-miniature secondary projectiles. But I'm just guessing. However, the drag function of a bullet in ballistic gelatin tends to agree with this analysis. Perhaps Peter Kasler could enlighten us? JHBercovitz@lbl.gov (John Bercovitz)
DCROWE@GTRI01.gatech.edu (06/18/91)
This discussion seems to be based on the assumption that supersonic shock waves are the mechanism for tranferring energy to the target. Hydraulic pressure is the more common mode, and it accounts for the large damage channels that are observed to vastly exceed the bullet size.