Ergo supplied you with the link about the Towers and why they collapsed so fast and straight down. Did you at least read the article?
Did you miss Physics class in high school....
Acceleration due to gravity If you drop an object relatively near the Earth, it will speed up according to the acceleration due to gravity (g).
Object speeds up When you let go of the object, its velocity is zero.
Since g = 32 ft/s2 = 9.8 m/s2, the velocity will be 32 ft/s (9.8 m/s) after one second. Because the object is accelerating, the velocity after 2 seconds will be 2 x 32 ft/s = 64 ft/s (19.6 m/s). After 10 seconds, the velocity will be 10 x 32 ft/s = 320 ft/s or 98 m/s. You can see how the velocity of the object gets faster and faster.