[mod edit: duplicate post]

He's correct. You only need to consider basic physics to realize this.

Firstly, I shall presume you are familiar with the concept of a stress-strain curve. In mechanics, this is sometimes referred to as  Hooke's Law curve. The stress tensor for steel is described as a highly inelastic, up to the yield point, which is very high, but with very little strain, after which it starts to buckle. Now, there is a second-order differential equation that links temperature with the yield strength point, because the expansion causes an effect that is known as viscoplasticity, which steel exhibits above 720 Kelvin. This means that the yield point for steel at temperatures exceeding this is significantly lower than normal. There is a double-effect associated with this. A jet will sever most of the columns, and, in fact, it severed roughly 60% of the columns in question, on the floor/s in question. This means, for the floor sitting below, the thermal expansion induced will cause an inward buckle. The important point to remember here is that the critical load, that is, the stress at which the strain induces buckling, is about 10 times smaller for a multistory buckling, because the critical load decreases proportionally to the distance from the pivot at which force is applied. This effect induces a "crush down". This effect is well known. The WTC are not the only high-story buildings to fall as a result. The kinetic energy of the upper stories falling through the ejected floor is greater than the absorption capacity of the lower story (taking away the gravitational potential energy lost as a result of the shortening of the building). If this occurs, the kinetic energy being transferred by the upper part of the building will be transferred to the part beneath it. If the kinetic energy being transferred to the lower columns (which have also deformed, albeit not to as great an extent, due to differential thermal expansion) exceeds the elastic . This is combined with the fact that compaction results in the loss of GPE, which must be converted into KE, by the law of conservation of energy. It is for this reason that the civil engineering community has concluded, rightfully, that even a displacement of the upper section by half a meter will result in the collapse of the building. This force being exerted by the upper section of the building on the exposed beams prior to their yielding, is called the crushing force.

In other words, there was a multipart factor combination required to induce the transfer of KE from the upper to the lower load beams. (1) The differential expansion of the columns as a result of fire. Since the temperature of the fire exceeded 720K, the material will exhibit a viscoplastic response to stress, also called "creeping". At this temperature, the yield point for steel drops by 85%. (2) The ejection of a floor by the impact caused the dissipation of GPE. (3) The stress redistribution that resulted from the severing of most supports upon impact, added to the fact that the supports have force being exerted over a greater distance from the anchored points, causes a lateral buckle. Thus the third condition (4) Multistory buckling of exposed columns, where the force being exerted is greater than the load capacity for the exposed columns by an order of magnitude.

The GPE, given as E=mgh, that is at the floor in question, can be found on a load against displacement graph. The energy transferred is therefore found by the integration of this area under the graph . Thus for a displacement s of a piece of tower, the energy criterion is [Int]F(s)ds. This is critical so pay attention. There is one criterion for preventing the chain reaction of collapse that results from the transfer of kinetic energy of impacting mass. The kinetic energy of the impact mass must be less than the net energy loss during one story being crushed. That in turn is calculated by the area under the force-load graph. In the case, of 9/11, the crushing force decreased quickly in response to the displacement of the upper piece of the building as it fell through the ejected floors. The primary reason for the sharp decline of F against s was the plastic buckling, due to the fact that temperature was hot enough for the metal to act as viscoplastic. As a result, the upper area fell, with little resistance, into the lower area, with the compaction resulting from the crushing of the floors in between.  As such, the total energy dissipation (found by integration) minus the GPE lost due to the compaction, was smaller than the kinetic energy which was transferred by the upper part smashing into the standing section. This is enough to trigger collapse. Since the GPE lost was quite large due the high degree of compaction and large volume of ejecta, the kinetic energy transferred exceeded this value.

 The tower, as we have seen, collapsed progressively from the top down, that is, once the top section fell through the ejected floor, the compaction and the rate of transfer of kinetic energy was sufficient for the building to collapse from the top down. As we have seen, this was caused by a multifactorial combination of thermally-induced expansion of steel columns, which decreased the yield and induced viscoplasicity, added to the shearing of insulation by the application of perpendicular force on the material by the impact, the severing, or severely weakening, of 60% of the columns by the impact on the floor, resulting in a load redistribution, the ejecting of a floor causing a dissipation of GPE, ensuring that the kinetic energy exceeded the elastic load capacity of the floor beneath it. If explosives had been planted at strategic points around the tower, with the aim of simulating these effects allowing for the accretion of mass to induce collapse, then this effect would not have been observed, primarily because (a) crush-down collapse results from a compressive force being applied from the upper part of the standing structure on the lower part and b) the application of force by ejecting a floor too low to the ground will not result in crush-down collapse. If multiple ejecta points were designated within the building itself, then instead of crush-down, more likely, it will result in the building falling over, which is dangerous in demolition work, and, obviously, not what happened on 9/11.

I can see you know how to cut and paste but your attempt at an intellectual smokescreen is really pathetic.

Your reasoning cannot explain the fact that WTC 7 collapsed without being hit by plane or debris and not having any serious fires.

He might as well have said pigs fly. It's a ridiculous argument, spouted by a probable bigot.

If you weren't a coward, you wouldn't scapegoat Muslims.

Real atheists embrace science and logic, not Neocon lies.

Um...articulation?

I have a suggestion for you. You could admit right now that you are not sufficiently qualified in mechanical engineering or physics to hold this conversation and leave before it just gets embarassing.

In fact I did take 3 physics courses, got A's in each one. But that's immaterial since falling objects, when they encounter solid objects connected to bedrock, do slow down. Yet the twin towers did not. Furthermore, the presence of numerous particles of thermate (military grade explosives, patent owned the US military) in the WTC dust is pretty damning.

No serious fires? According to eyewitnesses and film, the entire building was on fire by mid-afternoon. This, coupled with the debris damage from earlier in the day, caused the collapse, according to a recent report.

The debris damage to WTC 7 is actually evidence for an uncontrolled collapse of the WTC. Any demolitions would've minimized fly so that it was non-existent.

     Ux,  #7 went down after the twin towers, hit the deck and wiped out the underground supports integrity. Notice the collapse went sideways toward the twin towers.  In laymans terms (which I prefer) it pulled the rug out from under #7's feet.

Ah. I see. You believe it wasn't designed to be a controlled demolition, but was designed to look like an uncontrolled collapse.

Thermate is not an explosive. It is an incindiary. It's essentially thermite (powdered aluminum and metal oxide) with some sulfer. In other words, thermate would do exactly what the jet fuel was hypothesized to have done: melted the internal support structures. The physics of what you propose (a thermate demolition) would be essentially the exact same as the fuel-based demolition, only with thermate along the core instead of jet fuel.

So the validity of the free-fall evidence would be about the same for both scenarios.

I certainly hope your physics is better than your chemistry. Thermate employs the thermite reaction, a displacement reaction between Aluminium and a metal oxide, usually iron. It does not explode. It is an incendiary. It would produce an identical scenario to fuel-induced burning.

Try as you might to obfuscate an obvious controlled demolition, any child can see it was imploded. The video even shows squibs.

The owner of the building announced it was going to be "pulled", which is demolitions jargon for imploded. BBC News said it had collapsed 30 minutes before it had. Word had gone out WTC was going to be collapsed.

You're resisting coming to the conclusion that 9/11 was an inside job. Why not just tell us which reason it is:

• fear the truth, or
• work for the government, or
• are bigoted against Muslims, or
• have some vendetta against religion, or
• are cashing in from the homeland security boon, or
• by some strange chance you're a Zionist.

Be honest.