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Post by turbonium on Feb 5, 2007 2:46:34 GMT -4
The debris was forcefully ejected from the building - in every direction. Any debris ejected downward would be able to travel down faster than objects in a pure free-fall. You can't measure the speed of collapse for the tower by comparing it to the debris speed. Anything ejected with a downward component would by definition hit the rest of the building first. No. Debris has to be ejected out from the building due to an external force other than gravity. That force may originate from various sources -explosives, impact from collapse, etc. A piece of debris that is ejected downward from that force will travel downward faster than if that piece of debris was in a purely gravity-driven free fall. Pretend you were on the rooftop of a WTC tower, pointed a gun down towards the ground far below and fired a bullet. Then grab another bullet and simply drop it from the rooftop. Obviously, the bullet fired from the gun will travel downward much faster then the free-fall bullet. An external source (gun, explosives, impact) of energy (force) on an object can propel the object downward (or in any direction) faster than purely free fall speeds. It's really not a debatable point.
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Post by gillianren on Feb 5, 2007 4:30:52 GMT -4
To a point. However, bullets are slowed down by friction all the time. (It's one of the reasons certain wounds look the way they do.) If the bullet starts out going faster than terminal velocity, it will actually slow down in flight before it hits the ground.
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lenbrazil
Saturn
Now there's a man with an open mind - you can feel the breeze from here!
Posts: 1,045
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Post by lenbrazil on Feb 5, 2007 19:23:06 GMT -4
Anything ejected with a downward component would by definition hit the rest of the building first. No. Debris has to be ejected out from the building due to an external force other than gravity. That force may originate from various sources -explosives, impact from collapse, etc. A piece of debris that is ejected downward from that force will travel downward faster than if that piece of debris was in a purely gravity-driven free fall. Pretend you were on the rooftop of a WTC tower, pointed a gun down towards the ground far below and fired a bullet. Then grab another bullet and simply drop it from the rooftop. Obviously, the bullet fired from the gun will travel downward much faster then the free-fall bullet. An external source (gun, explosives, impact) of energy (force) on an object can propel the object downward (or in any direction) faster than purely free fall speeds. It's really not a debatable point. This would only be true if the debris had been ejected at a downward angle something not seen in the videos I’ve seen. It is ejected pretty much horizontally and then begins to fall. The vast majority of debris can be seen out pacing the collapse. Since the initial downward velocity of the ejected debris is zero or close to zero there is no reason for it to noticeably out pace the collapse unless the collapse was significantly below free fall speed. Also if I'm not mistaken if the horizontally ejected debris and collapse fell at the same speed we would expect the debris to slightly lag behind the building because it would have started falling downward a fraction of a second later. Perhaps a small amount of debris was ejected downward at an angle but that would explain the bulk of the debris falling faster than the rest of the building. As already noted, even several CT sites including 911 Research, which is probably the best researched one, acknowledge that the collapse lasted longer than free fall time. www.911myths.com/html/wtc_collapse_time_estimates.html
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Al Johnston
"Cheer up!" they said, "It could be worse!" So I did, and it was.
Posts: 1,453
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Post by Al Johnston on Feb 5, 2007 20:13:19 GMT -4
I think it was Galileo who first demonstrated that an object will hit the ground at the same time whether dropped from rest or given an initial sideways velocity.
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Post by bazbear on Feb 17, 2007 3:10:36 GMT -4
I think it was Galileo who first demonstrated that an object will hit the ground at the same time whether dropped from rest or given an initial sideways velocity. Yep, I've heard this example used with firearms too; if you could simultaneously drop a bullet out of hand and fire one parallel to a "flat" surface (ie a perfectly flat firing range) , they would both hit the ground at the same time.
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Post by turbonium on Feb 17, 2007 7:10:08 GMT -4
This would only be true if the debris had been ejected at a downward angle something not seen in the videos I’ve seen. It is ejected pretty much horizontally and then begins to fall. The vast majority of debris can be seen out pacing the collapse. Since the initial downward velocity of the ejected debris is zero or close to zero there is no reason for it to noticeably out pace the collapse unless the collapse was significantly below free fall speed. Also if I'm not mistaken if the horizontally ejected debris and collapse fell at the same speed we would expect the debris to slightly lag behind the building because it would have started falling downward a fraction of a second later. Perhaps a small amount of debris was ejected downward at an angle but that would explain the bulk of the debris falling faster than the rest of the building. As already noted, even several CT sites including 911 Research, which is probably the best researched one, acknowledge that the collapse lasted longer than free fall time. www.911myths.com/html/wtc_collapse_time_estimates.html I still maintain that it's impossible to determine what free-fall speed actually is based on the debris. There are plumes of debris that stream out in a downward arc and race past other debris - not just past the building's upper line of collapse. The debris these plumes race past must be falling at free-fall speed, and the plumes must therefore be travelling faster than free-fall speed. Regarding your link - I've mentioned before that they are largely concerned with measuring the time for overall collapse, from start to finish. This method has many problems with determining accurate and quantifiable figures and calculations. When does it actually start to collapse? And worst of all - when does it actually reach the ground? It's impossible to measure with any degree of accuracy because it can't be seen through the massive clouds of dust and debris. Just this measurement alone must have a margin of error spanning several seconds. Estimates I've seen that consider a margin of error for initiation of collapse usually allow at least +/- 1 second for the South Tower, and +/- 2 or 3 seconds for the North Tower, which initiated collapse when the top section leaned several degrees from vertical. That's why there will always be a wide range of estimates, and no conclusive measurements will ever be agreed upon. But the method I am convinced is much better is calculating the collapse times over 10 to 40 floor sections. The advantages are obvious - (relatively) unobstructed views of the towers over a small midsection, more precise start time (ie: floor 65) and finish time (ie: floor 35). This also directly addresses the most important issue - determining the collapse speed, not the collapse time. If the collapses are measured to be free-fall speed, (or x 10th/sec +/- free fall speed), over 20, 30, or 40 floors, that makes the debate regarding overall collapse time a moot point. I haven't seen this method applied yet, but until it is, or another method just as good or better is, we only have a wide range of guesstimates that can't ever be resolved to any acceptable degree or accuracy. I also think, just from my own noodling, that the collapse speeds will be found to indeed be free-fall, if not faster. I hope it will one day be quantified with solid, reliable data.
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Post by gillianren on Feb 17, 2007 8:39:10 GMT -4
I still maintain that it's impossible to determine what free-fall speed actually is based on the debris. I admit that I spent most of the year I took high school physics playing board games (our teacher had two heart attacks in November, and our substitute for about half the year had a doctorate in theatre), but can't you figure out what free fall speeds for something should be using, you know, nothing but math?
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Post by PhantomWolf on Feb 17, 2007 21:28:07 GMT -4
Well really the whole issue is moot anyway since at least two videos of the collapse taken near the base (in one case byt a fire crew inside the building) clearly shows that it took at least 17 secs and maybe up to 20 sec for the towers to come down.
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Post by jaydeehess on Feb 18, 2007 1:03:25 GMT -4
Turbonium,
Construct a short tower out of 2 X 4's with a flat plywood top about 8 inchs square. Now pour a pail of gravel on top of it and note how it falls off to the side, some of it even bouncing across the top first. Now line up small colored pebbles along the edge and repeat with the pail. Do the colored pebbles all land after the pieces of gravel from the pail?
NO!
Debris that originates within the building cannot be ejected 'downward' without hitting the building.
Even a perimeter column cannot move in a downward direction unless it either has been broken away from the rest of the column AND falls away from the building , OR the portion of column below it has been removed first.
Bullets travel at supersonic speeds and air resistance is a much trickier issue. Perhaps you should use an example of throwing a ball down over the side as opposed to dropping one over.
this is where air resistance comes into play. Heavy, dense objects such as concrete or steel will indeed out pace lighter, less dense dust, paper, wood, gryprock because the gravity force on an object is fixed and based on mass while the air resistance increases with velocity, and surface area. Take two objects of identical shape and mass but one of them has 10 times the mass of the other and drop them from a high point and the heavier one will always hit the ground faster than the other one( in an atmosphere).
One need only calculate the terminal velocity of two objects to see this will be inevitable.
mass = m a = g Cd is coeffiecient of friction rho is the density of air v is the velocity A is the surface area perpendicular to travel
at terminal velocity mg=Cd(A)(rho)(v2)(0.5)
(mg)/ (Cd)(A)(rho)(0.5)=v2
Now if all things remain equal but the mass of another object is 10times that of an identically shaped object then
Since g, Cd, A, rho and 0.5 are going to be constant we can write
m(K) = v2 for the small mass
10m(K) = v'2 for the larger mass
(0.1)v'2 = v2 0.32 v' = v (or v'= 3.2v)
The less dense object has a terminal velocity that is is 1/3 that of the denser object. It will stop acellerating much sooner than the dense object.
So, yes some things will outpace others in an atmospherics fall.
the heaviest and densest objects will fall at very close to the same rate they would if there was no atmosphere at all since the drag force is such a small percentage of the gravitational force on them.
Further to this, drive down a dusty gravel road on a calm day and note how long it takes for the dust to settle back down to the roadbed. It takes hundreds of times longer than it would in a no atmosphere condition because the terminal velocity of a dust mote is so low that it takes minutes to travel the few feet to the ground. Throw a brick out the window and it will take a fraction of a second to fall the same distance.
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Post by jaydeehess on Feb 19, 2007 19:40:53 GMT -4
Further to this:
Any object that starts falling before another object will outpace the second one.
Drop a hammer from 20 feet and drop a second hammer from 10 feet when the first hammer has reached 15 feet(it is still 5 feet above the starting point of the second hammer) and the first hammer will still reach the ground first.
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