Tower Collapse Questions for Critical Thinkers

The amount of deceleration is minimal at best. Maybe a few nano-seconds would be my guess.

And not, not the mass of the entire flors below it, just the one immeadiatly below the failure point.

That is 2 strawman arguments in one day. Kyle, you need to go to bed.
 
triforcharity said:
Ok, so total of a 1/10 of a second??
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Perhaps if you drop the brick from high enough.

Of course the tops of the towers compared to the bottoms weren't like bricks compared to eggs. A better analogy would be a tube of 110 eggs, pull one towards the top out of the stack, and watch how quickly that decelerates. Besides, that isn't even considering the fact that the "eggs" at the bottom of the towers were much stronger than the ones at the top.
 
kylebisme said:
It is mostly instantaneous, but it is declaration regardless.


Yet when you add an egg for every floor, that deceleration adds up.
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Don't forget that the falling mass is increasing with every floor that gets crushed.

We know that the debris that fell outside the towers was falling faster than the collapse front, therefore the collapse front did decelerate as it hit each subsequent floor, but it never came to rest until it reached the ground.


Just checking: Is this 2009, or did I just dream the last three years- like some Antipodean Bobby Ewing?
 
kylebisme said:
Can anyone provide an example outside the events of 9/11 where one collection of mass crushes another under the force of gravity alone, without decelerating on the way down?
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Dave Rogers explained this to you some pages ago. Tony Szamboti had it explained to him many times in the 'missing jolt' thread.

The collapse zones at WTC were tilted, eccentric. There were thousands if not millions of small decelerations in the impact areas as structural members and connections broke, but none of these - and no collection of these - was sufficient to lead to a measureable 'jolt' from the point of view of the roofline. All that was detectable was that the buildings came down at less than freefall. The deceleration was 'averaged out'.

The verinage CD's were very different in this respect. The upper sections fell fair and square on the lower, as was intended. What's more they were reinforced concrete buildings. The deceleration or 'jolt' was detectable.

Analogies involving sand and cardboard boxes will not help you understand anthing here. The scale, structure and materials involved are in the 'back yard' range of daily experience.
 
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Indeed.

There is, of course, a reason why structural engineers require 4 years of university level study followed be several years of post graduate on-the-job training before they get to play with this kind of stuff.

Hint: it's not because it's easy and you can work it out with sand and carboard boxes.
 
kylebisme said:
Surely you mean the force F exerted by the lower block on the upper one subtracts from the acceleration of that upper block? Like if you jump down onto a gymnastics mat it subtracts from your acceleration, slowing your fall. We have two forces here, but only one acceleration.
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The distinction is purely a matter of convention. Adding a positive number to a negative number is the same as subtracting a positive from a positive. It's more rigorous to talk in terms of vectors, but in this case all the forces act in one dimension so we can talk about addition and subtraction in a scalar sense. There is a resultant acceleration, and vector arithmetic can be done with acceleration as well as with forces (though doing it with forces is more correct).

kylebisme said:
Rather, the upward force of the lower block is expected to be greater than the weight of the upper block, the lower block having held that upper block in place prior to the section between the two being pushed out. It is this net upward force which results in the deceleration you mention. Agreed?
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Agreed.

kylebisme said:
Now, from the bold is where I'm not following you at all. You are speaking of the floor supports being destroyed in instances, with periods of free fall between them. I'd like to see the measurements you refer too, but in these collapses I've been speaking of, it is not just floors falling one on top of each other, but the whole structure being crushed down, concrete walls and all. There is no chance of freefall after the initial collision, as there is constantly mass acting as resistive force in the way. Also, I dug up video of this Balzac-Vitry collapse which I'm guessing might be the one you refer to, but surely you are not suggesting there is any free fall after the initial collision in that?
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It's an approximation to treat the collapse as a series of discrete shocks, but in the case of the Balzac-Vitry demolition it's not a bad one. This is not argued from a theoretical approximation, but from the actual data; the Balzac-Vitry demolition shows a decrease in downward acceleration at the initial impact, then a greater acceleration as it falls through the height of the supporting walls, then another decrease as it hits the next floor. The conclusion to be drawn is that most of the resistance takes place as the floors collide, that a storey of supporting walls collapses and ceases to offer significant resistance, and that the upper block then falls, approximately in free fall, until it impacts on the next floor.

Again, this isn't theorising, it's observation. I'm not suggesting that there's near free-fall after the original collision; I'm observing it.

Dave
 
kylebisme said:
momentum = mass x velocity.

force = mass x acceleration

The two are related, but not the same; mass doesn't doesn't gain force though momentum. (That really isn't quite true, but the increase is immeasurably small until coming very close to the speed of light, which isn't rightly relevant here.)
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Sorry, kylebisme, but that paragraph is so scientifically illiterate that it's almost painful to read it. Mass does not "gain force" through any means, as the two are dimensionally different. Mass increases close to the speed of light, but this is not "gain(ing) force". Mass, however, exerts force through changes in its momentum; force may be defined as the rate of change of momentum with time, and therefore the momentum of a mass may be used as a measure of its ability to exert force. The lower blocks of the WTC towers needed to exert sufficient force to counteract the effects of gravity on the upper block - which they were capable of doing, of course - but at the same time they had to exert sufficient force to reduce the momentum of the upper block to zero before being compressed to the point of failure. This they were not capable of doing, even in their undamaged state - which they were very far from at thhe moment the collapses began.

Dave
 
kylebisme said:
It's not pedantic, it is the crucial difference between momentum and acceleration. Mass gains force though acceleration, not momentum. While the momentum changes as mass falls, the acceleration is the constant force of gravity.
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I really think you need to go back to school and learn some elementary physics. You're embarrassing yourself by posting this sort of word salad. "Mass gains force through acceleration, not momentum" is quite literally meaningless.

Dave
 
Dave Rogers said:
I really think you need to go back to school and learn some elementary physics. You're embarrassing yourself by posting this sort of word salad. "Mass gains force through acceleration, not momentum" is quite literally meaningless.

Dave
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I have only high school physics but I can see that is total nonsense.
 
kylebisme said:
The brick decelerates when it hits the egg and starts accelerating again from there.
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Wrong. The acceleration of the brick decreases very slightly when it hits the egg, but is still downward. You will at no point see the downward velocity actually decrease (which is what is meant by the word "decelerate"). Therefore, this is a trivial example of "one collection of mass crush[ing] another under the force of gravity alone, without decelerating on the way down".

kylebisme said:
Surely you aren't suggesting the bottom portions of each tower was like a giant egg?
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If truthers can use pizza boxes, chicken wire and filing trays...

Whether or not there are any relevant similarities, they follow the same laws of physics. I'm not using the brick-and-egg analogy to explain the collapses, I'm using it to try to teach you the physics involved.

Dave
 
kylebisme said:
The brick decelerates when it hits the egg and starts accelerating again from there. Surely you aren't suggesting the bottom portions of each tower was like a giant egg?
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Look, it's pretty simple. The towers' tops should have fallen sideways because of "the law of path of least resistance," right? This "law", should also apply to a brick falling on an egg. I.e. the brick should go round the egg. In reallity that doesn't happen. Explain, please.

And now you are heading into '"the law of path of least resistance" apllies not to bricks and eggs, but does apply to WTC towers' territory. A rather predictable evasion. I saw it coming when the brick-egg challenge was posed.
 
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kylebisme said:
I've had no reason to really look into it in detail, but while reading Makey's whitepaper I saw he suggested at least 500,000 tons, and and notes it was estimated to be carrying at least 2/3s of that at the time by NIST. Note of course that is the whole building, each floor has it's own limit too.
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I'm positive Ryan made no such claim, as it was nowhere near 500,000 tons. Typically a commercial office space would have floors capable of carrying 150 lbs/sq ft. At ~40,000 sq. ft. that means each floor could handle about 3000 tons evenly distributed. They certainly were not rated at 25,000 lb per sq. ft. And certainly nowhere near that much weight when it has velocity!

Now, what do you think the weight of the upper block was?
 
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Hokulele said:
Calculate how much deceleration you expect based on your claims and how that would affect the collapse times.
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It's a function of how fast a Republican can say "clunkety-clunk". Didn't you learn your truther fizziks?
 
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