Cuddels, they topple buildings. Experts like Brent Blanchard and also Jowenko can tell you that, I will not post movies from it because you can find it if you want.
Huntsman, I rechecked and another expert Loizeaux, he says in fact:
The explosives are used as the catalyst and gravity is the engine.
Once it goes it goes, the tremendous amount of kinetic energy will break extremely strong structures. I was more referring to the initial moment, potential energy doesn't break the complete structure, it is the kinetic energy/momentum etc. Strictly speaking I was wrong that I said that the potential energy is only used to get the building down because once it is transformed to kinetic energy that is also used to break some other stuff.
And energy is energy isn't it. Let me correct that.
And in fact Greening already shows that once you only need a fraction of the kinetic energy (ok you are right: comes from the potential energy) to break the structure. The collapse time in the TT case differs only a little bit.
Let me end this posting by noting that for wtc7 both a controlled demolition and a structural failure are consistent with the laws of physics.
However if you know how difficult the technique is (there are only about 20 CD companies) to end with a pile of rubble then I'm more thinking about the first one.
I copy paste something from howstuffworks:
Blasters might also overestimate the amount of explosive power needed to break up the structure, and so produce a more powerful blast than is necessary. If they underestimate what explosive power is needed, or some of the explosives fail to ignite, the structure may not be completely demolished. In this case, the demolition crew brings in excavators and wrecking balls to finish the job. All of these mishaps are extremely rare in the demolition industry. Safety is a blaster's number-one concern, and, for the most part, they can predict very well what will happen in an implosion.