I don't think that the MOAB killed anyone.

[Jehanne]

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.  

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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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.