Chris,
Thanks for your correction vis a vis John Gross.
As an aside, it is not clear from any of the videos that I've seen (including the firefighters & the "streams of molten steel, like lava" video) that the people on the video are relating first person observations.
It has been my experience that people who have seen something themselves are generally pretty clear on the issue. "I was here... I saw this..."
The firefighter specifically says "YOU'd get down below and YOU'd see molten steel, molten steel, running down the channel rails ..."
This phraseology does NOT prove that he is relating something second hand. But it is also not clear that he is relating something first hand either.
This same observation appears to apply to most (or all) of the videos that I've seen. And in several cases (Leslie Robertson, for example), when followed up, the quote turns out to be erroneous.
Yes, your interpretation is wrong.
The dots above the straight line velocity curve do NOT mean that the acceleration at that point is higher than g, or that dots below the curve are at a lower acceleration than g. You cannot tell anything about the acceleration by looking at any one velocity data point. You must look at at least 2 points.
The slope of the red line happens to be very close to G acceleration. It makes a handy reference.
What you have to look at is the SLOPE of the line that connects each pair of dots. If the slope between any two dots is steeper than the red line, then you can say is that "the data suggests that the average acceleration over this interval was higher than G". If the slope between any two dots is less steep than the red line, then the data suggests that the average acceleration over that interval was less than G."
There are two possible explanations for the value being above G:
1. Data error. (Note: ALL experimental data has error bands associated with it.)
2. The average acceleration really was >G over that interval.
It is not possible to tell from NIST or Chandler's data which of these conditions is true. More careful analysis (frame by frame, instead of every 15th or so frame) strongly suggests that the "over G" acceleration was true for two brief intervals, totaling about 1.2 seconds or so, during Stage II.
The explanation for this is simple. "G" acceleration is an upper limit for an "isolated body", i.e., a body that has only one force acting upon it - gravity. (That is, nothing else touching it.) If other forces are being applied to that body, then it's downward acceleration can be >G.
The external wall of WTC7 was absolutely NOT an "isolated body". It was unquestionably attached to lots of other components thru the floor trusses. According to NIST, those other components started falling earlier than the external wall gave way. It is entirely possible, even likely, that those components' earlier start transmitted additional downward forces on the outer walls which could appear as "over G" acceleration.
I hope this helps.
Tom
PS. BTW, I had a pretty good laugh listening to Chandler's comments about your video.
EVERY SINGLE comment he made about you being "unknowledgeable in physics" applies in spades to his being "unknowledgeable about engineering". He should listen to his own cautions about going public & issuing statements that are out of his realm of expertise.
Thanks for your correction vis a vis John Gross.
As an aside, it is not clear from any of the videos that I've seen (including the firefighters & the "streams of molten steel, like lava" video) that the people on the video are relating first person observations.
It has been my experience that people who have seen something themselves are generally pretty clear on the issue. "I was here... I saw this..."
The firefighter specifically says "YOU'd get down below and YOU'd see molten steel, molten steel, running down the channel rails ..."
This phraseology does NOT prove that he is relating something second hand. But it is also not clear that he is relating something first hand either.
This same observation appears to apply to most (or all) of the videos that I've seen. And in several cases (Leslie Robertson, for example), when followed up, the quote turns out to be erroneous.
Yes, your interpretation is wrong.
The dots above the straight line velocity curve do NOT mean that the acceleration at that point is higher than g, or that dots below the curve are at a lower acceleration than g. You cannot tell anything about the acceleration by looking at any one velocity data point. You must look at at least 2 points.
The slope of the red line happens to be very close to G acceleration. It makes a handy reference.
What you have to look at is the SLOPE of the line that connects each pair of dots. If the slope between any two dots is steeper than the red line, then you can say is that "the data suggests that the average acceleration over this interval was higher than G". If the slope between any two dots is less steep than the red line, then the data suggests that the average acceleration over that interval was less than G."
There are two possible explanations for the value being above G:
1. Data error. (Note: ALL experimental data has error bands associated with it.)
2. The average acceleration really was >G over that interval.
It is not possible to tell from NIST or Chandler's data which of these conditions is true. More careful analysis (frame by frame, instead of every 15th or so frame) strongly suggests that the "over G" acceleration was true for two brief intervals, totaling about 1.2 seconds or so, during Stage II.
The explanation for this is simple. "G" acceleration is an upper limit for an "isolated body", i.e., a body that has only one force acting upon it - gravity. (That is, nothing else touching it.) If other forces are being applied to that body, then it's downward acceleration can be >G.
The external wall of WTC7 was absolutely NOT an "isolated body". It was unquestionably attached to lots of other components thru the floor trusses. According to NIST, those other components started falling earlier than the external wall gave way. It is entirely possible, even likely, that those components' earlier start transmitted additional downward forces on the outer walls which could appear as "over G" acceleration.
I hope this helps.
Tom
PS. BTW, I had a pretty good laugh listening to Chandler's comments about your video.
EVERY SINGLE comment he made about you being "unknowledgeable in physics" applies in spades to his being "unknowledgeable about engineering". He should listen to his own cautions about going public & issuing statements that are out of his realm of expertise.
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