Evidence that the lower block provided resistance until something else removed the resistance from the lower block.
Let's take a look.
Looking at the video, the lower block was unable to stop the downward movement of the mass of the upper block and in the absence of bomb explosions. And, it is very clear in the video that WTC1 is not falling at free fall speed.
Edited by skyeagle409, 24 May 2013 - 01:44 AM.