Three columns supported the east penthouse. But it is much more likely that at least two and possibly three supporting columns were "taken out" simultaneously. NIST (the government agency assigned to investigate the building collapses) attributes the collapse of the east penthouse to the failure of a single column, in a complex scenario involving thermal expansion of beams supporting the column. Shortly before the ultimate collapse of the building the east penthouse and the columns beneath it suddenly gave way. This is one of the Building 7 explosions that occurred long before it fell. Suddenly they are startled by a very loud, unmistakable explosion. One such explosion is recorded in a video clip where several fire fighters are gathered around a pay phone calling home to assure their families they are alright. There were explosions in Building 7 heard by many witnesses throughout the day. Since the fall was not slowed in the slightest, we can conclude that the force of interaction was zero. If the falling section of the building had crushed the lower section, the lower section would have pushed back with an equal but opposite force. It fell for about 2.5 seconds at a rate that was indistinguishable from freefall. It didn't just fall at something close to freefall. We know that the falling section of Building 7 did not crush the lower section of the building because the top section of Building 7 fell at freefall. However, amazingly, this is not what happened when Building 7 "collapsed" on 9/11. A typical controlled demolition exploits this fact: the crushing force of the falling section of the building contributes to the demolition, and reduces the amount of explosives that are needed. When the top section of a building collapses one would expect the falling section to crash into the lower section and exert a large force on it, like dropping an anvil on your toe. If an object is observed to be in freefall, we can conclude that nothing in the path exerts a force to slow it down, and by Newton's third law, the falling object cannot be pushing on anything else either. Therefore, while an object is falling, if it exerts any force on objects in its path, those objects must push back, slowing the fall. What if a heavy object falls through other objects, breaking them as it goes? Newton's third law says that when objects interact, they always exert equal and opposite forces on each other. (If several forces are acting at once they are combined to give a "net" force.) If the downward acceleration of a falling object equals the acceleration of gravity, then the net force is the gravitational force alone any other forces must add up to zero. Isaac Newton showed that the acceleration of an object is governed by its mass and the net force acting on it. The "acceleration of gravity" actually varies slightly from place to place. After 2 seconds its speed will be 64 ft/s. After 1 second its speed will be 32 ft/s. (The awkward unit, feet per second per second is commonly abbreviated ft/s2.) When an object is dropped, the speed is initially zero, but it immediately starts speeding up. Gravity causes freely falling objects to increase their speed by about 32 ft/s per second. The acceleration achieved by all falling bodies, apart from air resistance, is called the "acceleration of gravity." The rate we are talking about is actually the "rate of increase of speed," how quickly the speed builds up, called acceleration. The rate we are referring to is not a "speed," because for a falling object the speed is constantly changing. Galileo was the first to describe the amazing fact that, apart from air resistance, all objects fall at the same "rate." If you have not experienced this fact directly, try dropping a large rock and a pebble side by-side. In this article, he covers one of the more crushing pieces of evidence that disproves the official account, the freefall of Building 7. With his background as a teacher of physics, David Chandler has made invaluable contributions to the quest for 9/11 truth and justice, helping to make technical aspects of the controlled demolition of all three World Trade Center buildings more accessible to lay persons. Physics Teacher David Chandler Introduction to David Chandler's "Freefall and Building 7" by Mike Cook
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