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The physics toolkit

Several posts have been removed to AAH. Remain civil and avoid personal attacks and bickering.
Replying to this modbox in thread will be off topic  Posted By: Cuddles
 
newton3376 said:
This discussion alone should be enough to prove to you that it is NOT high school level physics.
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I'd just like to note that we were doing problems like this, and much more complicated ones, aged 16. If harmonic motion, including forcing and damping, is not taught until second year university at the earliest, it appears that education in the US is even worse than I thought.
 
A quick note before I hit the beach for a couple of weeks...
HARRIS’ SHOCK AND VIBRATION HANDBOOK said:
The simplest model for a physical system that will respond to a shock or vibration excitation is given by a rigid mass supported by a linear spring, commonly referred to as a single-degree-of-freedom-system.

An ideal system may be considered undamped for mathematical purposes; in such a system the free vibration is assumed to continue indefinitely.

In any real system, damping (i.e.,energy dissipation) causes the amplitude of free vibration to decay continuously to a negligible value.
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Cuddles said:
I'd just like to note that we were doing problems like this, and much more complicated ones, aged 16. If harmonic motion, including forcing and damping, is not taught until second year university at the earliest, it appears that education in the US is even worse than I thought.
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Shhhhhh.. don't tell FEMR or Newton that...they will argue with you until red-faced...even though the question itself came from a journal aimed at High School students.....and was answered by multiple freshmen in college...without added other factors or complicating the question. they just can not accept this.

Bottom line: FEMR answered wrong...point , blank, no additional comment needed. Denail won't make his answer correct.

They will also argue that the actual answer is not the true answer based on nothing more than a lack of understanding....then argue for their obscure answer by trying to invent 'fluff' on top to make it seem as if they actually have a clue. I think Newton does have a clue..I know FEMR does not.

This is much like how FEMR thinks that the collapse of WTC had to be a CD because as he worded it "there was no energy to propel debris to the roof of the Winter Gardens'.....

Duh...The "C" in CD = controlled..so a CD would never propel an body past the control zone..and, of course, the explosion would be audible to all....

I notice FEMR never bothered to answer my second question..and in fact---wait for it---Has changed his original wrong answer to a new wrong answer.:jaw-dropp From 1/1.76 to now 1/1.78.....
 
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Cuddles said:
I'd just like to note that we were doing problems like this, and much more complicated ones, aged 16. If harmonic motion, including forcing and damping, is not taught until second year university at the earliest, it appears that education in the US is even worse than I thought.
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I do not believe you that you were doing differential equations at age 16, so spare me the drama....

People (often anonymous internet posters) always say crap like this about the US....and then they end up in the tutoring center once they get to Calc 1 or Calc 2 because they are failing the class.....then we have to tutor them through their math and physics classes even though they supposedly had a "better" education then we Americans did.

Regardless of what ANY of us did or didn't do at a certain age.....this problem is NOT a highschool physics problem.....differential equations is simply not a high school physics topic, sorry.

So please save useless and unverifible comments like this for someone else....no one is interested or impressed and it doesn't contribute to the original discussion in the slightest.
 
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newton3376 said:
I do not believe you that you were doing differential equations at age 16, so spare me the drama....

People (often anonynous internet posters) always say crap like this about the US....and then they end up in the tutoring center once they get to Calc 1 or Calc 2 because they are failing the class.....then we have to tutor them through their math and physics classes even though they supposedly had a "better" education then we Americans did.

Regardless of what ANY of us did or didn't do at a certain age.....this problem is NOT a highschool physics problem.....differential equations is simply not a high school physics topic, sorry.

So please save useless and unverifible comments like this for someone else....no one is interested or impressed and it doesn't contribute to the original discussion in the slightest.
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I think cuddles was being sarcastic.
 
FEMR...I'm going to try and take a look at your argument this weekend...I'll dig through the thread and go through your posts and let you know what I think....
 
from here --->>>> http://www.physicsforums.com/showthread.php?p=2815761&posted=1#post2815761

This is just too freakin classic: The wording is a little bit weird, but yes, it's exactly F0/2.

You wasted all day for 2 days - trying to prove that a correct answer was an incorrect answer...following the fraud femrs lead and looking foolish in the process.

For a tight thread, all of these coefficients are not going to play a big role in a single oscillation

I find it funny how when you psoted to the linked physics forum, it took 2 posts to correct you, and put FEMR in his place...and...notice how his incorrect answer is now changed to another incorrect answer?

LOL...this is hillarious.
 
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Carll68 said:
from here --->>>> http://www.physicsforums.com/showthread.php?p=2815761&posted=1#post2815761

This is just too freakin classic: The wording is a little bit weird, but yes, it's exactly F0/2.

You wasted all day for 2 days - trying to prove that a correct answer was an incorrect answer...following the fraud femrs lead and looking foolish in the process.

For a tight thread, all of these coefficients are not going to play a big role in a single oscillation

I find it funny how when you psoted to the linked physics forum, it took 2 posts to correct you, and put FEMR in his place...and...notice how his incorrect answer is now changed to another incorrect answer?

LOL...this is hillarious.
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Neither one of you is correct. Femr2 is just less wrong than you are. Two correctly analyze this problem you need two things:

1) Damping ratio
2) Increase in yield stress due to fast strain rates.
 
If the collapse initiation is different from the NIST findings how does that prove explosives? It just proves that the collapse and fires that started them are all part of a chaotic event.
 
Carll68 said:
Wrong...FEMR is 100% incorrect.

The answer I supplied is 100% correct.

End of story.
http://www.physicsforums.com/showthread.php?p=2815761&posted=1#post2815761
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You're using an equation of motion that is based on assumptions that do not apply in the real world. The actual equation of motion is:

mu'' + cu' + ku = p(t) where u is displacement

The post you've linked to has set c = 0. Femr2 has given c (the viscous damping coefficient) a definition and a reasonable one at that. I don't know if he arrived at that through investigoogling or if he took a graduate level engineering course in Dynamics of Structures. I would guess it is the former as he is unable to provide a rational defense of his answer except linking to papers.

Unfortunately for you, I've taken those classes, and used the knowledge garnered in them in my profession. Which means when you say that he's 100% wrong, I know that you're full of :rule10. He tried to apply real-world mechanics to a complicated problem. You claim he doesn't understand physics because he made a different assumption and a perfectly valid assumption no less. This would be akin to you inquiring what the distance of a block was after travelling for 10/s and having an initial velocity 10 m/s and then claiming he was 100% wrong because he made an assumption on what frictional forces that block was under. Based on that, it's safe for me to assume that you don't know what the :rule10 you're talking about or that you're intellectually dishonest.
 
Newtons Bit said:
You're using an equation of motion that is based on assumptions that do not apply in the real world. The actual equation of motion is:

mu'' + cu' + ku = p(t) where u is displacement

The post you've linked to has set c = 0. Femr2 has given c (the viscous damping coefficient) a definition and a reasonable one at that. I don't know if he arrived at that through investigoogling or if he took a graduate level engineering course in Dynamics of Structures. I would guess it is the former as he is unable to provide a rational defense of his answer except linking to papers.

Unfortunately for you, I've taken those classes, and used the knowledge garnered in them in my profession. Which means when you say that he's 100% wrong, I know that you're full of :rule10. He tried to apply real-world mechanics to a complicated problem. You claim he doesn't understand physics because he made a different assumption and a perfectly valid assumption no less. This would be akin to you inquiring what the distance of a block was after travelling for 10/s and having an initial velocity 10 m/s and then claiming he was 100% wrong because he made an assumption on what frictional forces that block was under. Based on that, it's safe for me to assume that you don't know what the :rule10 you're talking about or that you're intellectually dishonest.
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For the question asked, the solution is exactly F0/2.

No if's, and's, or buts.

Point, blank, end of story.

He was and is and forever will be wrong in his answer, based on the question posed.
 
Carll68 said:
For the question asked, the solution is exactly F0/2.

No if's, and's, or buts.

Point, blank, end of story.

He was and is and forever will be wrong in his answer, based on the question posed.
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No, it's not, and I've explained why. Your inability to even acknowledge why different assumptions matter is mind-boggling.
 
Carll68 said:
from here --->>>> http://www.physicsforums.com/showthread.php?p=2815761&posted=1#post2815761

This is just too freakin classic: The wording is a little bit weird, but yes, it's exactly F0/2.

You wasted all day for 2 days - trying to prove that a correct answer was an incorrect answer...following the fraud femrs lead and looking foolish in the process.
Click to expand...

I never tried to prove anything Carll68....I simply wanted a few questions answered...

Carll68 said:
For a tight thread, all of these coefficients are not going to play a big role in a single oscillation

I find it funny how when you psoted to the linked physics forum, it took 2 posts to correct you, and put FEMR in his place...and...notice how his incorrect answer is now changed to another incorrect answer?

LOL...this is hillarious.
Click to expand...

No one corrected me, since I never made a claim....I was asking a few questions about some details.....you couldn't answer them, but others have.
 
Captain_Swoop said:
If the collapse initiation is different from the NIST findings how does that prove explosives? It just proves that the collapse and fires that started them are all part of a chaotic event.
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,,,,,,,, I have made a similar point several times now in this thread.

All femr has been able to do is put a finer detail to the behaviour of the structure just prior to and through the fall of the north face.

He has also managed to illustrate that none of this finer detail can in any way aid in deducing exactly what caused the progression of the collapse to become a global collapse.

Indeed it also illustrates one reason WHY NIST did not bother to conduct a more thorough analysis of the final global collapse, it would not have, nor could it have, made any difference to their conclusions.

BTW, in the whole suddenly applied force on a thread bit. The glaring simplification of no friction force was the first thing that 'sprang' to mind.
The greatest friction force due to air resistance would occur as the downward motion reachs a maximum. This would occur very soon(dare I say , as soon as) the extra mass is applied. It would quickly lessen as velocity dropped, reach zero as velocity reached zero and then become a downward force as the thread rebounded and everything moved upward. The definition of a damping effect, and one reason why in first year physics labs an experiment that has the student slowly apply more mass to a thread in order to deduce the Young's Modulus of the thread material. No significant, overshoot, or oscillation, or damping forces to make such a calculation difficult. I do recall that we had to time how long it took for each stretch to finish( the time to reach a new equilibrium)

There is however only a 'thin' application of this concept to the subject of the thread(that is the forum string of posts which we refer to as a thread)

Secondly, some have wondered if this new force was constant. Well if this force is due to a suddenly applied, added mass that is not removed at some point then yes, of course it is constant since the extra force is due to the added mass.
 
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