I don't know, as far as an intuitive conclusion or suspicion is concerned I could see how people would wonder just how deep a concussive blast can penetrate the earth.  OTOH, the comments offered seem to betray a fundamental (but simple) misunderstanding of physics.  It's not just the bomb that Jeh got wrong, bullets as well..and the same thing wrong in both cases.  In that light, it's easy to see why "the physics don't make sense" from Jehs POV.  If we're being screwed with..it's a damned fine job, lol.

More fun facts about bullets. The average distance for a projectile to accelerate to the speed of sound within a barrel is 4-6 inches...and this might give folks some insight into the general shape of a pistol..any shorter or slower than that and you'll need a subsonic round to prevent excessive tumbling, which reduces (and can reduce to zero..a miss) applied force to target. Thankfully, the projectile is small but dense, and the distances are short..but if you had a supersonic round you wouldn;t want to hit your target before that round reached it's maximum velocity. Essentially, someone climbing into the barrel gets shot that much less hard than someone standing at the end of it..lol. The same is true, for most of the same reasons, when it comes to airburst bombs.

(April 15, 2017 at 8:23 am)Jehanne Wrote: And, so, my question remains, "What was Trump's real motive in using this weapon?"

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(April 15, 2017 at 8:23 am)Khemikal Wrote: The misunderstanding seems to centered around the munitions detonation height.  The reason we do that, is to allow blast time to accelerate before it reaches target.  Otherwise, some potential force is wasted/lost.  That, is "the physics" of it.  These bombs don;t lose applied force over that distance, they gain it.  Detonating the munition in the mouth of the access tunnels would have less effect, not more.

I just don't think that an above-ground explosion against a below-ground target makes much sense, from a physics POV.  As for "gaining force over distance" that would be equivalent to saying that a bullet gains speed after leaving the muzzle of a gun (neglecting its vertical drop, of course!), and that is false.

I've seen nothing to indicate tRump had anything to do with the decision to use this particular kind of device against this target. That was a call made by the military. This bomb was designed just for this type of target, and if there's one thing we've gotten good at in the past several thousand years it's designing weapons to be efficient at destroying stuff including people.

Gaining force over distance isn't a good description of what happens in the shock wave of an air burst. In an air burst there is an intesified area of higher pressure generated at some distance from ground zero due to an effect called Mach Stem. When the incident wave from an air burst hits the ground it is reflected. The reflected wave is traveling in an area of lower pressure and higher temperature generated by the incident wave so the reflected wave travels faster than the incident wave. The area where these two waves meet generates an area of greatly enhanced pressure.

The way T.rump handled that question about approving the attack shows that he had nothing to do with it. The man can't lie very well.

Gaining applied force over that distance is exactly what you just described...so? Agree to agree?

(April 15, 2017 at 8:41 am)Khemikal Wrote:

(April 15, 2017 at 8:23 am)Jehanne Wrote: I just don't think that an above-ground explosion against a below-ground target makes much sense, from a physics POV. 

You must be using a novel sense of "makes sense".  I think that you're speaking intuitively.  The ground does offer cover from indirect fire, that's why we build bunkers...but that protection is not absolute or uniform.  The bomb in question is a big fuckin bomb precisely -because- the ground does offer protection.  If it were a smaller bomb, or detonated at the wrong height, it would have less penetrative ability.  

Quote:As for "gaining force over distance" that would be equivalent to saying that a bullet gains speed after leaving the muzzle of a gun (neglecting its vertical drop, of course!), and that is false.

Bullets -do- gain speed from the time that the blast cap is struck until some distance x, variable by caliber and load..which sometimes does and sometimes doesn't exceed the length of the barrel....depending on the length of the barrel......that's actually a key concern in barrel and round design.  Ideally, the barrel is as long or slightly longer than the acceleration window..in order to deliver all usable force to a single point - accuracy.  

Think about the corollary.  If you doubt that bullets accelerate, or that blast waves accelerate..you are are indicating your belief that the speed at which either moves is -instantaneously- achieved at detonation.......

I am saying that a bullet undergoes rapid acceleration and then gradual deceleration after it leaves the muzzle of a gun, neglecting its vertical drop, of course.  The same analogy would apply to a bomb, also.

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(April 15, 2017 at 9:13 am)popeyespappy Wrote:

(April 15, 2017 at 8:23 am)Jehanne Wrote: And, so, my question remains, "What was Trump's real motive in using this weapon?"

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I just don't think that an above-ground explosion against a below-ground target makes much sense, from a physics POV.  As for "gaining force over distance" that would be equivalent to saying that a bullet gains speed after leaving the muzzle of a gun (neglecting its vertical drop, of course!), and that is false.

I've seen nothing to indicate tRump had anything to do with the decision to use this particular kind of device against this target. That was a call made by the military. This bomb was designed just for this type of target, and if there's one thing we've gotten good at in the past several thousand years it's designing weapons to be efficient at destroying stuff including people.

Gaining force over distance isn't a good description of what happens in the shock wave of an air burst. In an air burst there is an intesified area of higher pressure generated at some distance from ground zero due to an effect called Mach Stem. When the incident wave from an air burst hits the ground it is reflected. The reflected wave is traveling in an area of lower pressure and higher temperature generated by the incident wave so the reflected wave travels faster than the incident wave. The area where these two waves meet generates an area of greatly enhanced pressure.

Waves can interfere constructively or destructively, and so, pressure would be greater at certain points than at others.  However, below ground (which was where ISIS was, supposedly), would not be effected very much, assuming, of course, that their tunnels were sufficiently deep, which was the whole point of my OP.

(April 15, 2017 at 9:35 am)Khemikal Wrote: Gaining applied force over that distance is exactly what you just described...so?  Agree to agree?  

Kinda sorta. The over pressure is the highest when the two waves first meet which is at some point out from but very close to ground zero. Jehanne is right though in that it loses energy the further from that point you get. That being said the over pressure that results from an air burst is still higher than it would be in a ground burst because there is no reflected wave adding to the effect.

(April 15, 2017 at 9:58 am)popeyespappy Wrote:

(April 15, 2017 at 9:35 am)Khemikal Wrote: Gaining applied force over that distance is exactly what you just described...so?  Agree to agree?  

Kinda sorta. The over pressure is the highest when the two waves first meet which is at some point out from but very close to ground zero. Jehanne is right though in that it loses energy the further from that point you get. That being said the over pressure that results from an air burst is still higher than it would be in a ground burst because there is no reflected wave adding to the effect.

Which is why I am wondering (out loud) why they dropped the damn thing in the first place?

The Pentagon cannot hurt the CIA's assets; i.e ISIS.

(April 15, 2017 at 9:52 am)Jehanne Wrote: I am saying that a bullet undergoes rapid acceleration and then gradual deceleration after it leaves the muzzle of a gun, neglecting its vertical drop, of course.  The same analogy would apply to a bomb, also.

Right, and before the round reaches the full potential of that rapid acceleration it would be less than productive to apply it to target (or release it from the barrel, specifically in the case of rifles).  The same analogy -does- apply to a bomb and -is- the reason we airburst some munitions.  The maximum applied force is not realized either at the blast pin in a rifle -or- right at the origin of the bombs explosion for a moab.  

Quote:Waves can interfere constructively or destructively, and so, pressure would be greater at certain points than at others.  However, below ground (which was where ISIS was, supposedly), would not be effected very much, assuming, of course, that their tunnels were sufficiently deep, which was the whole point of my OP.

So, in essence, you don't doubt that it works, you think that it's effective depth penetration tapers off with depth?   Well, ofc it does.  Again, that's why this one is so damned big. It will still only go so far, so deep. We don't advertise accurate stats for shit like that, but the notion that anyone inside the tunnel when it went off has about as good a chance as a chilean miner, assuming they survived the initial impact...is pretty solid.

Quote:Which is why I am wondering (out loud) why they dropped the damn thing in the first place?

Because it's the right munition for the target. A relatively deep tunnel network positively screams out for ground penetrating ordinance. The deeper the tunnel, the bigger the bomb. Some are designed to, in essence, plunge themselves to a certain depth before detonation...but amusingly, this only works on a shallow bunker (because the warhead can only get so far into the earth). Others, like the moab, are designed to create an immense wave of force that the ground carries down to target.

(April 15, 2017 at 9:52 am)Jehanne Wrote: Waves can interfere constructively or destructively, and so, pressure would be greater at certain points than at others.  However, below ground (which was where ISIS was, supposedly), would not be effected very much, assuming, of course, that their tunnels were sufficiently deep, which was the whole point of my OP.

Yes waves can interfere with each other when they are out of phase. That's how active noise cancellation works. The effect can also be used in radar receivers to eliminate ground clutter. But that's not what is happening here. With the Mach Stem effect you essentially have a strong wave being pushed from behind by a faster wave.

No the MOAB isn't the best conventional weapon at our disposal for use against hardened targets or deep tunnels and caves. That would be the 30,000 lb. GBU-57A/B Massive Ordnance Penetrator (MOP). A penetrator type weapon designed to explode after contact once it is deep into the ground/bunker. The MOB has not been used in combat yet. That doesn't mean the MOAB wasn't effective against this target. The Afgan forces that investigated site reported that the bomb collapsed 3 tunnels/caves so apparently it worked.

ETA: Apparently the angle the incident wave meets the reflective wave determines how effective the Mach Stem effect is, but it is still an additive effect no matter how acute the angle is.