On Warheads

Artillery shells bursting over the Gaza Strip.  From NYT.

The above picture shows artillery shells bursting over the Gaza Strip.  It clearly shows the "bombs bursting in air," which most people never really think about.  Modern warheads (missiles, artillery shells, tank shells) actually explode before they reach their target.  In the case of shells meant to kill people, they burst into a bazillion hot fragments upon exploding, a concept pioneered by a Canadian named Shrapnel.  As you can see from the picture, the bursts result in a neat cone of forward projected shrapnel, spraying a particular area, and not just in every direction from the burst.  This is because modern munitions include shaped charges that push the explosion in a particular direction.

So, every time you see an artillery shell explode in a movie, and everyone get blown this way and that, that is total crap.  The reality is that hot metal flies from the sky at 4000-5000 meters/second, penetrating houses and getting people hiding in their little holes.  

The same goes for missiles- they explode before reaching aircraft and spray projected shrapnel in a little cone.  You'll never see that in a movie.  No one would understand why the missile detonated prematurely.

HEAT tank round.  Note the inverted cone in the nose, with the backside packed with high explosives.

Finally, tank warheads (so-called "heat", not sabot projectiles made of uranium) are a special and particularly awesome form of shaped charge.  They are based on the "Explosively Formed Penetrator" concept, where an explosion is detonated behind an inverted dome or cone, where the middle of the inverted shape is pushed out and goes through a geometric inversion, resulting in a sharp-looking projectile (made of either superplastic superheated metal or even plasma) travelling at something like 5-10 times the speed of sound (5000-10000 m/s).  This projectile will penetrate almost anything, but not being strictly solid, it breaks up after travelling for significant distances in the air.

Improvised munitions along these lines (IEDs) can penetrate military armor, and are used by insurgents all over the world.  Design of effective EFP type weapons can require sophistication though, and this recalls some aggressive claims of the US government that Iran was training people how to make them, and supplying them with parts and explosives.

In summary, there are no more "bombs" that go off when they hit the ground and blow everything up in a big fiery mess.  That hasn't happened for 200 years or more.  Modern warheads are much nastier.