The WTC contained about 400,000 cubic meters of concrete, most of which became a powder with a grain size below 5mm diameter, and much of it was below 1mm diameter. How much energy was needed to pulverize that much concrete?

We cannot know exactly because there are too many unknowns, but we can certainly make a good guess. For example we could assume that 100 concrete floors in each tower were 60 by 60 meters wide by 100mm thick, and that concrete became particles of 5mm diameter.

The only energy available to pulverize the concrete was the "potential energy" of the buildings due to the force of gravity. However, the videos show that no piece of concrete fell more than a few meters to the floor beneath it before turning into powder. This means each concrete floor picked up enough energy during the fall of a few meters to convert itself to a fine grain powder. Is that possible without an additional energy source (eg, explosives)?
(The links at the end show video sources)

Here is a technical description of the tower: http://www.staff.ncl.ac.uk/john.knapton/WTC.htm

Here are a good description of the buildings and their collapse: J. McMichael's analysis

2) The videos show that no floor fell more than a few meters before shattering to dust. If we assume the concrete was made properly, how far would a concrete floor 60 by 60 meters wide by 100mm thick have to fall before it picked up enough energy to pulverize itself?

3) Is there enough potential energy in any building to pulverize its concrete if a fire or explosion were to initiate its collapse at a few of the upper floors?

With the endless fighting between nations, the world needs a way to determine when a building has been secretly destroyed with explosives.

If there were no explosives, then everybody making such accusations should stop it.

Conversely, if explosives were used, and if nobody can figure it out, the people who did it will be laughing:

"Can you believe that not even the world's best physicists could figure out that we put explosives in the buildings? We will have to do this again!"

Update: when Jerry Russell wrote that analysis he did not believe that explosives were used. He has since changed his mind. His latest conclusions are at his web site:
http://www.911-strike.com/demolition.htm

After Russell changed his mind, it made me wonder about his guess of 30,000 pounds of explosives. That would be 15,000 pounds per tower, or about 136 pounds (62 kg) on each floor.

It is interesting to wonder how many weeks people were working in those buildings while those thousands of pounds of explosives were being placed inside.

Anybody want to try refining Russell's guess of 30,000 pounds to a more accurate value?

If you have something to add, send it to erichuf@aol.com

These two sites have videos of the collapse:
http://media.us.ametrika.com
http://wtc.pkl.net/