WTC 6 took a direct hit from the North Tower, WTC 7 took a glancing hit from the North Tower. WTC 6 was hit with a massive amount of the North Tower.  I think Buildings 4 and 5 had partial collapses as well when the Towers fell.  The idea there was only 3 buildings destroyed that day is wrong. This is all about the power of Potential Energy becoming Kinetic Energy.  When you lift massively heavy things high up in the air, you are storing a lot of Potential Energy.   How much?  People estimate the potential energy in each tower to be equivalent to more than 100 tons of Dynamite.  That's 2 million pounds of dynamite. In each building.