[Elsie]

I saw the upper thirty-five floors of the first tower to fall actually tip past 25 degrees from vertical, as a ridged body.

My physics classes taught me that a rigid body will NOT tip over unless there is a sideways force acting upon it.

What were the upper level winds like that day?

What speed?

What direction?

[MHGinTN]

Try watching the videos still available on Youtube. The damage to that tower was at a corner, the floors above (35 floors) had a sag in parallel to the vector of gravity at that corner. A commercial building is around ten feet thick (space) so the tilt began as the support for the floors above the damnage failed and the structure gave from vertical at that corner.