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Szamboti's Missing Jolt paper

3bodyproblem said:
They tell first year students to avoid using the term deceleration as it only confuses. It's best to use negative acceleration. I avoided the term for a bit, but succombed.

A falling body undergoes an acceleration of 9.8 m/s^2 due to the force of gravity. Anything less than this is a negative acceleration, ie. an acceleration in the opposite direction. This means a falling body that increases its rate of decent slower than expected due to gravity is undergoing negative acceleration due to a retarding force. The kinetic energy absorbed in the deformation reduced the rate of decent.

I'm not sure of what you are looking for anymore. From what you have posted I am starting to think you are looking for a complete arrest (v=0 m/s) in the collapse at initiation or some time soon after.
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All of this makes sense to me. This is what I remember from high school physics. I particularly found amusing the statement that a falling mass would require deceleration before transferring any kinetic energy whatsoever.

Eight hours a day, Tony. I swear by it.
 
Tony Szamboti said:
Wrong! Deceleration is a negative acceleration. Anything less than 9.8 m/s^2 but greater than zero is just lesser positive acceleration [viz. this is somehow a different class of behavior than "negative acceleration."]. To transfer kinetic energy the impacting object needs to decelerate. The upper block of WTC 1 never did that, it continued to increase it's velocity throughout it's fall. The lower acceleration was due to resistance which failed at loads less than those of the static weight of the structure.
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(Emphasis and clarification added)

Irreducible Delusion.

My god, man, this is elementary Physics. Draw a force-diagram.
 
boloboffin said:
All of this makes sense to me. This is what I remember from high school physics. I particularly found amusing the statement that a falling mass would require deceleration before transferring any kinetic energy whatsoever.

Eight hours a day, Tony. I swear by it.
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Both you and 3bodyproblem are wrong. The static load is already being decelerated by -1g or -9.8m/s^2 when it is held in position. The weight of an item on earth is it's mass times the acceleration due to gravity. You can't have an amplification of that weight or force without decelerating the mass, or negatively accelerating it if you prefer, without the rate being greater than -9.8m/s^2.

As for your doubts about deceleration being required for kinetic energy transfer from an impacting object, you need to attempt to show mathematically how kinetic energy could be transferred without losing velocity. Good luck!
 
AZCat said:
I told him to do this over at DU when he made the same argument, and he refused. I don't think he knows (or remembers) how to draw a free-body diagram.
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I'm inclined to believe you're right.

To Tony, I'm going to leave that arrow in the quiver. In case you ever make the big time, I'll make one then and trot it out for a larger audience for a bigger laugh. If you want to prevent that, or actually learn something, I encourage you to take the opportunity I'm giving you -- try it for yourself and see where you went wrong. Any physics student should be able to see it.
 
Tony Szamboti said:
Yes, it does leave 0.3 of the weight of the upper block to go into the connections. The problem, as I am sure you are well aware, is that the building structure below was designed to handle several times the weight of the upper block. The only way to overload it with the statically insufficient load above is with an impulsive load, which requires deceleration of the impacting mass.
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It was designed to hold the load when the structure was intact.
 
Tony Szamboti said:
Both you and 3bodyproblem are wrong. The static load is already being decelerated by -1g or -9.8m/s^2 when it is held in position. The weight of an item on earth is it's mass times the acceleration due to gravity. You can't have an amplification of that weight or force without decelerating the mass, or negatively accelerating it if you prefer, without the rate being greater than -9.8m/s^2.

As for your doubts about deceleration being required for kinetic energy transfer from an impacting object, you need to attempt to show mathematically how kinetic energy could be transferred without losing velocity. Good luck!
Click to expand...

OK, I see where he's deliberately confusing the issue.

What Tony is saying is that, as the object falls, since at all times it continues to accelerate downward the opposing force at all times is less than m g, the static load. This reasoning is correct.

He then turns around and says that, because of this, there is no "force amplification." In other words, this means the momentum of the object is irrelevant, and collapse would continue regardless of the upper block's speed -- the magnitude of momentum is only relevant if the opposing force reduces it, such that a race condition exists between countering the momentum and failing the lower structure. This is also correct.

Where it falls down is in two critical aspects:

First, as we've noted dozens of times in this thread, the structure is not falling flat and level, squarely onto intact columns. Only a few columns at a time resist the collapse. Steel only compresses a tiny fraction before its strength is completely gone. So the fact that the average resistance through a range of motion is much less than the static strength is normal, perfectly expected, and agrees with the above.

Second, as we've also noted repeatedly, Tony's argument only works in unlimited precision. There are going to be tiny but sharp periods of deceleration, lots of them, that average to much less than one g. The time resolution needed to see this greatly exceeds what we have available.

This has no bearing on the comments I highlighted in my last posts, however. Even though the descending block is accelerating, and does so at a reasonable fraction of one g, that still means there is a strong opposing force inflicted by the lower structure. This force leads to a massive amount of damage in the lower structure. Saying that without seeing a true deceleration, there must be no damage inflicted, is totally stupid.
 
Tony Szamboti said:
Both you and 3bodyproblem are wrong. The static load is already being decelerated by -1g or -9.8m/s^2 when it is held in position. The weight of an item on earth is it's mass times the acceleration due to gravity. You can't have an amplification of that weight or force without decelerating the mass, or negatively accelerating it if you prefer, without the rate being greater than -9.8m/s^2.

As for your doubts about deceleration being required for kinetic energy transfer from an impacting object, you need to attempt to show mathematically how kinetic energy could be transferred without losing velocity. Good luck!
Click to expand...


Experiment 6
Elastic and Inelastic Collisions:

http://rds.yahoo.com/_ylt=A0geu.e4r...erphysics.phy-astr.gsu.edu/Hbase/elacol2.html

Hope this helps.
 
R.Mackey said:
OK, I see where he's deliberately confusing the issue.

What Tony is saying is that, as the object falls, since at all times it continues to accelerate downward the opposing force at all times is less than m g, the static load. This reasoning is correct.

He then turns around and says that, because of this, there is no "force amplification." In other words, this means the momentum of the object is irrelevant, and collapse would continue regardless of the upper block's speed -- the magnitude of momentum is only relevant if the opposing force reduces it, such that a race condition exists between countering the momentum and failing the lower structure. This is also correct.

Where it falls down is in two critical aspects:

First, as we've noted dozens of times in this thread, the structure is not falling flat and level, squarely onto intact columns. Only a few columns at a time resist the collapse. Steel only compresses a tiny fraction before its strength is completely gone. So the fact that the average resistance through a range of motion is much less than the static strength is normal, perfectly expected, and agrees with the above.

Second, as we've also noted repeatedly, Tony's argument only works in unlimited precision. There are going to be tiny but sharp periods of deceleration, lots of them, that average to much less than one g. The time resolution needed to see this greatly exceeds what we have available.

This has no bearing on the comments I highlighted in my last posts, however. Even though the descending block is accelerating, and does so at a reasonable fraction of one g, that still means there is a strong opposing force inflicted by the lower structure. This force leads to a massive amount of damage in the lower structure. Saying that without seeing a true deceleration, there must be no damage inflicted, is totally stupid.
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Yes - he's conflating two separate issues.
 
Tony Szamboti said:
As for your doubts about deceleration being required for kinetic energy transfer from an impacting object, you need to attempt to show mathematically how kinetic energy could be transferred without losing velocity. Good luck!
Click to expand...


Who said that Dorothy? the lion?, the tin man? or...

There was a change in velocity, at a rate of 2.94 m/s2 [up] from that which would be expected due to gravity alone.

It's you that seems to think there's a difference between negative acceleration and deceleration.
 
AZCat said:
Yes - he's conflating two separate issues.
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He certainly is. Just to make this clear, suppose we constructed a brand new structure just like a WTC Tower and started it collapsing, except this time we jerked each floor's columns free with cables at the exact instant the debris column arrived. In this contrived example, the structural strength opposing collapse is precisely zero.

But following his argument, we'd still see "jerks." While the strength is zero, we'd now be sweeping up new material, and transferring momentum from the descending mass to the stationary masses. This can only result in a temporary deceleration of the descending mass, driven by conservation of momentum.

Yet we don't see one. Again, this is because of the tilt -- we accelerate the lower mass piecemeal, smeared out over a fraction of a second, so at all times the aggregate deceleration is less than one g. That's all we can measure.

There is no way to prevent conservation of momentum, not even with explosives. So we should see a "jerk" no matter what. What this proves, therefore, is (a) either geometry means there is no "jerk," like we've been saying all along, or (b) Tony's technique is insufficient to see any "jerk" in the first place. As it happens, both are true.
 
R.Mackey said:
He certainly is. Just to make this clear, suppose we constructed a brand new structure just like a WTC Tower and started it collapsing, except this time we jerked each floor's columns free with cables at the exact instant the debris column arrived. In this contrived example, the structural strength opposing collapse is precisely zero.

But following his argument, we'd still see "jerks." While the strength is zero, we'd now be sweeping up new material, and transferring momentum from the descending mass to the stationary masses. This can only result in a temporary deceleration of the descending mass, driven by conservation of momentum.

Yet we don't see one. Again, this is because of the tilt -- we accelerate the lower mass piecemeal, smeared out over a fraction of a second, so at all times the aggregate deceleration is less than one g. That's all we can measure.

There is no way to prevent conservation of momentum, not even with explosives. So we should see a "jerk" no matter what. What this proves, therefore, is (a) either geometry means there is no "jerk," like we've been saying all along, or (b) Tony's technique is insufficient to see any "jerk" in the first place. As it happens, both are true.
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The use of the term "jerk" might be confusing to some (it was to me, initially). When I took the various physics courses that covered dynamics, we used the term "jerk" to describe a change in acceleration of an object (i.e. the third derivative of position). Here, Tony seems to be using to describe a near-instantaneous change in velocity. Could we use a different term rather than "jerk"?
 
To get closer to the reality of what happened (at the risk of totally going off topic), just as the upper section didn't hit uniformly but in a concentrated way, would it be correct to say that the core section eventually did exactly the same thing to the descending mass? We're all familiar with the spire left after the bulk of both buildings fell. As the debris layer began to accumulate, wouldn't it have leveled out relative to the core? That would have caused the core to punch through the debris level at the lower levels, particularly as core columns increased in size and mass.
 
I think the term is appropriate. That's what he's looking for -- a sudden change in acceleration, i.e. a large "jerk."

That's also part of his problem. He's looking at position information and trying to find the third derivative. This requires multiple successive observations (no less than four) and uncertainties propagate very badly. It's always better to average (i.e. integrate) than difference (differentiate) wherever possible... The result is that his uncertainties are large, limiting his ability to even see a "jerk" in the first place.
 
R.Mackey said:
I think the term is appropriate. That's what he's looking for -- a sudden change in acceleration, i.e. a large "jerk."

That's also part of his problem. He's looking at position information and trying to find the third derivative. This requires multiple successive observations (no less than four) and uncertainties propagate very badly. It's always better to average (i.e. integrate) than difference (differentiate) wherever possible... The result is that his uncertainties are large, limiting his ability to even see a "jerk" in the first place.
Click to expand...

I guess so, except he's seems to be looking for two large jerks back to back, to signal the beginning of resistance (negative jerk) and end of resistance (positive jerk) of a part of the structure, rather than one jerk. So now he needs even more data points, because the two appear rather close chronologically.
 
Admittedly, I will not be adding anything constructive with this post.

I note that Mr. Szamboti received his Bachelor's degree from Villanova University. I am also a graduate of that fine institution, and the running gag in our department was that is was exceedingly important to identify the buildings and bridges that the engineering department designed, so that they could safely be avoided.

On behalf of all other students and teachers, past and present, of Villanova, I hereby apologize. Most of our graduates are competent, but now and then one slips through the cracks.
 
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