Recently I developed a very simple experiment. Take the cardboard tube from the center of a roll of toilet paper and stand it on end. Now place a full 1 gallon can of paint on it. The tube supports that static load, doesn't it? Now raise the can say 5 or 6 inches above the tube and drop it. What happens to the cardboard tube? Why?
The dynamic load of the moving paint can is many times greater than the static load of that same paint can not moving even though the actual weight has not changed. Crude I know but it helps to understand the difference between static and dynamic load which is crucial to understanding the collapse of the WTC towers. This is as you say, common sense physics.
Your experiment is a poor model of what happened to the Twin Towers. Invalid in fact. It assumes the mass of the upper (moving) portion remained constant (like the bowling ball) when in fact it increased in mass and momentum with each floor that it dropped through.
The specific structural failures in each of the twins were different but fundamentally you have a failure of a single floor which then causes the static load of the upper portion of the building to become a dynamic load at least 30 times greater (in the case of the South Tower) collapsing down onto the next floor below. That floor can not support a load like that so it collapses and becomes part of the dynamic load, and so on and so on and so on. The moving portion of the tower increases with every floor failure.
There was no free-fall speed in the Twin Towers collapses except for debris that was ejected from the sides of the buildings. You only need one working eyeball and the ability to tell time to confirm this. Example:
If the tower is free-falling, how about the ejected debris which is clearly travelling faster than the main mass of the building? Faster than free-fall? By what mechanism?
http://www.tampabay.com/resources/images...
http://i286.photobucket.com/albums/ll116...
NIST never said either of the Twin Towers achieved G and the 9/11 Commission did not go into the engineering aspects at all. That wasn't their job. This tells me you have not actually read either report and are just copying or mis-understanding stuff you found on conspiracy web sites or you just don't understand the material.
First off you have made many assumptions that are wrong.
First off if the towers fell at freefall speeds they would have come down in less than 3 seconds not 10.
Second since when was only 14% of one tower and 150% of the weight of the other tower on the base of the tower? The weight at the base by definition is 100%. It would have to be suspended by a baloon or somethig not to be.
Where is your proof that freefall speeds have been confirmed?
The footage shows one tower starting to collapse at 1:22 and still collapsing at 1:35 thats 12 seconds and counting. They were both about 400m tall which could take less than 9 seconds.
Therefore they were not in freefall.
The speed of collapse is irrelevant. In tall steel towers, the weight of the upper floors striking is not what collapses the tower beneath. Large buildings with many columns are complex, interconnected structural systems. When parts of the system are weakened, loads redistribute to other parts of the system.
Where is this "healthy" portion of the tower you are talking about? When you change the way columns and girders/beams are connected, you change the entire system - the way it is loaded, the way it resists those loads, and the way it will fail if that resistance is exceeded.
The NIST has never claimed anything which they cannot explain, and they are not claiming that the top quarter of the tower falling on the lower portion caused the collapse. Fire reduces the elastic limit of steel (this is a well studied and understood concept). This means the steel will exhibit plastic deformation at a lower load. When any member begins to deform like this, everything connected to that member is affected, bracing layouts are altered, column buckling loads are lowered.
Acceleration was less than free fall. The following report may help you understand.
As you yourself stated, even a pack of crackers slows down a bowling ball. How can some government agency be expected to devise something to overcome the massive structure of the lower floors. As a side note, who bowls with a 30 pound ball?
Putting some of your misconceptions aside, let's simplify things a bit; for now, let's say we not look at the towers as intricate structures and instead as stacks of blocks of some engineered material (each one story tall), not subject to wind loadings or any of the other myriad forces at work on a tower beyond just gravity itself. Each block is strong enough to support the weight of the material above it, and so long as everything is relatively motionless, this is fine. The blocks are in a state of static equilibrium.
Now, for some reason or other, one of our blocks is removed from our stack. The blocks below it, supported by the ground, continue to stay in static equilibrium. The blocks above it, however, are no longer supported by anything, and without the support to counter gravity, begin to fall, as such things tend to do. The question becomes how fast our falling blocks will be moving when they hit the block next below them.
Let's say our blocks are ten feet in height (roughly a story, though a story can easily be 12-15 feet). We know, from basic kinematic equations, that the blocks above will now be moving downward at about 25 feet per second (not counting for wind resistance, etc.). The question now becomes, what happens when the falling blocks contact the remaining static blocks?
Now we have to start looking at the makeup of the blocks themselves; since they're an analog for a mostly steel structure, let's say they have similar advantages and drawbacks. This means that they are slightly springy, but if we exceed the limit of their springiness, they will simply shatter. So, now we have to consider what that limit is.
The compressive yield strength of steel is about 22000 psi, while the Young's modulus is 29000 ksi. Since we're dealing in rough concepts at this point, let's use these values to get an estimate of how much our slightly springy block can squish before breaking. From that calculated value (my math says about 0.008 ft), and the calculated velocity from earlier, we can determine that the amount of force the blocks below would have to sustain to stop the fall without breaking would be somewhere on the order of 1300 times the weight of the falling blocks - in short, 1300 times the weight they were originally designed to support.
In short, once those upper stories started falling, there was no possible way for the stories beneath them to stop them.
The towers fell at less than free fall speed.
The towers did not fall at "free-fall speed".
Nnnnoooooo, when will the conspiracy theories stop!
How can 14% of one tower and 25% of the other tower, bring the healthy 75-86% rest of the tower down at freefall speeds. To go down at freefall you must have nothing underneath to resist it.
This is common sense physics, here's a little experiment you can do to see my point. Take a box of crackers and a 30 lbs bowling ball, set the box upright and drop the ball ontop. The bowling ball will freefall until it meets the resistance of the box of crackers and slow down. Now there's a difference between the two scenarios the bowling ball weighs at least 30 times more than the box of crackers. With the towers a quarter(or less) of the entire weight is said to bring the rest of the tower down at freefall. NIST has not explained or attempted to explain this. Debunkers will try to argue the massive force but remember there's even more massive resistance, other debunkers will try and make the collapse longer but NIST and the 9/11 commission have confirmed freefall speeds. How's this possible?
