Moderated Continuation - Why a one-way Crush down is not possible

[A W Smith]

Now the earth spin has been changed.

Paul

Don't laugh!
http://ocw.mit.edu/OcwWeb/Physics/8-01Physics-IFall1999/VideoLectures/detail/embed06.htm#transcript

Imagine that an object is falling towards the earth.
An apple is falling towards the earth from a height, say, of, hmm, I'd say 100 meters.
And let's calculate how long it takes for this apple to hit the earth which should for you be trivial, of course.
So here's the earth...
and the mass of the earth is about 6 times 10 to the 24 kilograms.
And here at a distance, h--
for which we will take 100 meters--
is this apple, m, which, say, has a mass of half a kilogram.
There's a force from the earth onto the apple and this is that force.
And the magnitude of that force is mg and that is 5 newton.
I make g ten and just round it off a little.
Now, how long does it take this object to hit the earth? So, we know that 1/2 gt squared equals h.
It doesn't start with any initial speed, so that is 100.
G is 10, this is 5, so t squared is 20.
So t is about 4½ seconds.
So after 4½ seconds, it hits the earth--
so far, so good.
But now, according to the Third Law the earth must experience exactly the same force as the apple does but in opposite direction.
So therefore the earth will experience this same force, f--
5 newton, in this direction.
What is the earth going to do? Well, the earth is going to fall towards the apple--
f equals ma.
So the force on the earth is the mass of the earth times the acceleration of the earth.
The force, we know, is 5.
We know the mass, 6 times 10 to the 24 so the acceleration will be 5 divided by 6 times 10 to the 24 which is about 8 times 10 to the minus 25 meters per second squared.
How long will the earth fall? Well, the earth will fall roughly 4½ seconds before they collide.
How far does the earth move in the 4½ seconds? Well, it moves one-half a earth t squared.
That's the distance that it moves.
We know a and we know t squared, which is 20.
One-half times 20 is 10 so that means this distance becomes that number times 10.
It's about 8 times 10 to the minus 24 meters.
The earth moves 8 times 10 to the minus 24 meters.
That, of course, is impossible to measure.
But just imagine what a wonderful concept this is! When this ball falls back to me the earth and you and I and MIT are falling towards the ball.
Every time that the ball comes down we're falling towards the ball.
Imagine the power I have over you and over the earth!
But you may want to think about this--
if I throw the ball up, going to be away from the earth I'll bet you anything that the earth will also go away from the ball.
So as I do this, casually playing--
believe me, man, what a glorious feeling it is--
earth is going down, earth is coming towards the ball.
The earth is going down and I'm part of the earth and I'm shaking this earth up and down by simply playing with this ball.
That is the consequence of Newton's Third Law even though the amount by which the earth moves is, of course, too small to be measured.

 

[Heiwa]

We've been found out.
Heiwa has proved that you cannot stop a moving car, airplane, bicycle, falling body, or even a ship!
Everything we tried to foist off as science has been shown to be naught but illusion. We are undone!

Don't worry! The total momentum of any group of objects remains the same unless outside forces act on the objects.

You see, when tfk's m drops off his bike and hits ground an outside force acts on m and stops it. It is the friction between tfk's m and the ground

Edited by Gaspode: 

Edited for civility - moderated thread

.

Same thing happens when upper part C of WTC 1 is supposed to one-way crush down lower part A of same WTC 1. Outside forces produce various effects that prevents a one-way crush down. Clearly not seen on all videos of the controlled demolitions of the WTCs.

Actually, momentum is only conserved in closed systems (a very theoretical contraption used in ivory towers) and WTC 1 was not such a system/tower.

 

[aggle-rithm]

Now the earth spin has been changed.

Paul

I recently saw a documentary that talked about measuring the length of a day. The length of a day actually fluctuates by a fraction of a second every day due to exactly such forces (mostly wind and ocean currents, but everything that moves adds a little momentum shift).

 

[tfk]

Heiwa,

Don't worry! The total momentum of any group of objects remains the same unless outside forces act on the objects.

.
You're full of baloney.

Momentum is always conserved. In every interaction in the universe. Every single one. From subatomic particles to galaxies. Without exception.

You can change the momentum of a single object by applying a force to it. The momentum is not conserved only if you don't consider the momentum change of the object applying the force.
.

You see, when tfk's m drops off his bike and hits ground an outside force acts on m and stops it. It is the friction between tfk's m and the ground

.
The momentum is conserved. The body falling off of the bike hits the ground. Equal & opposite forces exist between the earth & the body at all instants, according to Newton's First Law. That means that the impulse exerted on the first body (the falling bicyclist) is equal and opposite to the impulse exerted on the second body (the earth). And so the change in momentum of the first body (the cyclist) are exactly equal & opposite to the change in momentum 2nd body (the earth).
.

Same thing happens when upper part C of WTC 1 is supposed to one-way crush down lower part A of same WTC 1. Outside forces produce various effects that prevents a one-way crush down. Clearly not seen on all videos of the controlled demolitions of the WTCs.

.
Heiwa, you'll grasp at any straw, no matter how senseless.

Because momentum is always concerned, even if a bomb were to go off inside the towers, there would be zero change in total momentum of the pieces & parts.
.

Actually, momentum is only conserved in closed systems (a very theoretical contraption used in ivory towers)

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Yeah, right. "A very theoretical contraption used in ivory towers". Like every single REAL interaction in the REAL world.
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and WTC 1 was not such a system/tower.

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Yeah. It was. That is precisely why people use "conservation of momentum" in all collision analyses. Wow, you'd think that someone who claims to perform analyses of collisions at sea would know about that.

It's kinda equivalent to a carpenter not know how to use a hammer.

Stunning...

 

[Heiwa]

You can change the momentum of a single object by applying a force to it. The momentum is not conserved only if you don't consider the momentum change of the object applying the force.


The momentum is conserved. The body falling off of the bike hits the ground. Equal & opposite forces exist between the earth & the body at all instants, according to Newton's First Law. That means that the impulse exerted on the first body (the falling bicyclist) is equal and opposite to the impulse exerted on the second body (the earth). And so the change in momentum of the first body (the cyclist) are exactly equal & opposite to the change in momentum 2nd body (the earth).


Stunning...

Hm, we have a system - you/m on bicycle and the Earth/M. You/m move at velocity v relative Earth and the momentum of the system is m times v. No force is acting on you/m affecting your speed. In that system I agree the momentum is conserved. You will continue at speed v for ever - round and round!

However! You fall off bike, friction force between you/Earth makes relative velocity v=0. It was a heavy jolt! Momentum of system becomes 0 because a friction force acted on you/m and Earth/M during fall.

Note that the friction force was not there before/after your fall. Only during.

Evidently the momentum was not conserved as an outside force acted on the system and result was that the momentum became 0. It was not conserved.

Not too difficult to grasp. That's why a one-way crush down is not possible.

 

[Dave Rogers]

Same thing happens when upper part C of WTC 1 is supposed to one-way crush down lower part A of same WTC 1. Outside forces produce various effects that prevents a one-way crush down. Clearly not seen on all videos of the controlled demolitions of the WTCs.

Now, this is interesting. We know that the structural strength of the lower block is insufficient to decelerate the upper block to zero velocity; your paper claims otherwise but does so by arbitrarily assigning a part of the energy of the upper block to entanglement and friction and then dishonestly pretending that these do not exert forces downwards on the lower block. Since the lower block cannot be responsible for these "outside forces", what is, exactly?

Dave

 

[aggle-rithm]

Hm, we have a system - you/m on bicycle and the Earth/M. You/m move at velocity v relative Earth and the momentum of the system is m times v. No force is acting on you/m affecting your speed. In that system I agree the momentum is conserved. You will continue at speed v for ever - round and round!

However! You fall off bike, friction force between you/Earth makes relative velocity v=0. It was a heavy jolt! Momentum of system becomes 0 because a friction force acted on you/m and Earth/M during fall.

Velocity and momentum are two different things.

Note that the friction force was not there before/after your fall. Only during.

Right. The friction transfers momentum from the bicyclist to the ground.

Evidently the momentum was not conserved as an outside force acted on the system and result was that the momentum became 0. It was not conserved.

Yes, it was. The momentum of the bicyclist was transferred to the Earth, making a minute change to the rate of the Earth's spin. Such momentum transfers happen all the time; that's why the length of a day varies from day to day.

Not too difficult to grasp. That's why a one-way crush down is not possible.

If that's the basis of your theory, then your theory is based on a lack of understanding of basic physics.

 

[newton3376]

Hm, we have a system - you/m on bicycle and the Earth/M. You/m move at velocity v relative Earth and the momentum of the system is m times v. No force is acting on you/m affecting your speed. In that system I agree the momentum is conserved. You will continue at speed v for ever - round and round!

However! You fall off bike, friction force between you/Earth makes relative velocity v=0. It was a heavy jolt! Momentum of system becomes 0 because a friction force acted on you/m and Earth/M during fall.

Note that the friction force was not there before/after your fall. Only during.

Evidently the momentum was not conserved as an outside force acted on the system and result was that the momentum became 0. It was not conserved.

Not too difficult to grasp. That's why a one-way crush down is not possible.

Heiwa.....do you realize what you are saying here?

You are violating the conservation of momentum!!!!

You are claiming that one of most firm foundational laws of current physics is wrong.....do you really want to make that claim?

You are beyond all reason if you deny fundamental and foundational physics...

 

[Heiwa]

Now, this is interesting. We know that the structural strength of the lower block is insufficient to decelerate the upper block to zero velocity; your paper claims otherwise but does so by arbitrarily assigning a part of the energy of the upper block to entanglement and friction and then dishonestly pretending that these do not exert forces downwards on the lower block. Since the lower block cannot be responsible for these "outside forces", what is, exactly?

Dave

Well, first of all the structural strength of lower part, sorry, block A, is just a little better than the structural strength of upper part (block??) C. Reason why A is stronger than C is that A carried C before (and that C could never carry A).

You suggest that you + others know that the structural strength of A is insufficent to decelerate C to zero velocity - after dropping C on A from say a height of a few meters, I assume - even if A is stronger than C. In my papers I calculate the energy involved. It is not much - abt. 30 litres of fuel driving a diesel engine!

It would appear that you suggest that C can apply downward forces on A that will destroy A and you also suggest that I deny the existence of these forces. Evidently I do not deny the existence of these forces ... only that they will destroy A completely.

Reason for my position is that A applies upward forces on C (as per Newton 3) that are equal to the forces C apply on A. And as C is weaker and smaller than A, the forces A apply on C will decelerate C and deform/damage elements in C.

In the WTC 1 case the forces A applies on C would simply arrest C up on top of A. Happens every time you drop a small part C on a bigger part A of equal structure. Only on 911 it didn't happy. Thus this discussion about a conspiracy!

 

[Dave Rogers]

You suggest that you + others know that the structural strength of A is insufficent to decelerate C to zero velocity - after dropping C on A from say a height of a few meters, I assume - even if A is stronger than C. In my papers I calculate the energy involved. It is not much - abt. 30 litres of fuel driving a diesel engine!

This is a meaningless analogy that you like to throw around. In fact, the energy involved is more than the lower block can absorb, which is the only comparison that means anything. As i pointed out, unless you pretend that half the potential energy of the upper block mysteriously vanishes, there's enough energy from a single storey drop to strain the entire lower stucture beyond its elastic limit.

It would appear that you suggest that C can apply downward forces on A that will destroy A and you also suggest that I deny the existence of these forces. Evidently I do not deny the existence of these forces ... only that they will destroy A completely.

I didn't say you were denying their existence altogether, just that you pretended they're smaller than they really are. I said you were pretending half the energy from the initial one-storey drop and all the energy released during the compression of the lower structure simply disappeared without creating a downward force on the lower structure. Therefore, by pretending more than half the forces didn't exist, you claim the lower block survives.

Reason for my position is that A applies upward forces on C (as per Newton 3) that are equal to the forces C apply on A. And as C is weaker and smaller than A, the forces A apply on C will decelerate C and deform/damage elements in C.

But we know that the lower block doesn't have the strength to decelerate even the broken parts of the upper to a standstill. You've now, however, invoked some mysterious other force that will slow the upper block. We know it's not the structural resistance of the upper block. What is it, exactly? Is it just another attempt to twist reality to fit your preferred conclusion, like your ridiculous claim that the Ronan Point collapse started at the bottom, when every study ever made points out that it initiated near the top?

You're ignoring more than half the downward forces on the lower block, and now you've suddenly dreamed up a nonexistent upward force on the upper. You've decided that conservation of momentum is an obstacle to the conclusion you want, so you've thrown it away. And you talk about Newton's Third Law, but you've even thrown that away by assuming that more than half the upper block's potential energy is lost without doing work on the lower block. Incidentally, you've thrown away conservation of energy in the process.

Which physical law do you plan to violate next?

Dave

 

[Heiwa]

Velocity and momentum are two different things.



Right. The friction transfers momentum from the bicyclist to the ground.



Yes, it was. The momentum of the bicyclist was transferred to the Earth, making a minute change to the rate of the Earth's spin. Such momentum transfers happen all the time; that's why the length of a day varies from day to day.



If that's the basis of your theory, then your theory is based on a lack of understanding of basic physics.

I am glad that you agree that friction stops the bicyclist dropping off the bike. But are you really sure that the momentum of the bicyclist was transferred to the Earth affecting its momentum? Maybe the momentum became heat - global warming, you know?

 

[tfk]

I am glad that you agree that friction stops the bicyclist dropping off the bike. But are you really sure that the momentum of the bicyclist was transferred to the Earth affecting its momentum? Maybe the momentum became heat - global warming, you know?

.
Wow.

You don't know the difference between momentum and energy, eh?

That's telling...

Momentum doesn't turn into energy, Anders. Energy turns into other forms of energy. And when it does, momentum is STILL conserved.

This is freshman engineering theory, Anders. These are fundamentals.

How can you get this stuff so wrong? Did you take mechanics, dynamics, physics classes when you got your architecture degree?

Tom

 

[tfk]

Heiwa,

I've got a question for you.

The concrete floors of the towers were rated to carry about 30 psf live load. Including safety factor, their design was for 100 psf max. What do you think would have happened to them if you shoveled in 300 psf of scrap metal?

According to Greg Ulrich's estimates, if the upper block is destroyed when it falls onto the lower block, the mass of the upper block amounts to about 600 psf on the 98th floor.

Even ignoring the momentum, what happens when that 600 psf of debris is piled up on the 4" thick concrete floor? It collapses.

And what happens when that 600 psf, plus the mass of the collapsed 98th floor, then fall onto the 97th floor? Even without considering momentum effects? It collapses.

What component of the floors & cross trusses do you imagine is going to support the weight of the upper block? Because that weight AIN'T going to be supported by the columns...

Tom

 

[Heiwa]

.
Wow.

You don't know the difference between momentum and energy, eh?

That's telling...

Momentum doesn't turn into energy, Anders. Energy turns into other forms of energy. And when it does, momentum is STILL conserved.

This is freshman engineering theory, Anders. These are fundamentals.

How can you get this stuff so wrong? Did you take mechanics, dynamics, physics classes when you got your architecture degree?

Tom

I thought I made clear in post #1909 the difference between momentum and energy. Kinetic energy = momentum times velocity divided by 2. We all know that when the bicyclist, no names, just a bicyclist, with mass m drops off the bike, hits ground and friction decelerates the mass m to velocity 0, the kinetic energy is transformed into heat, which is just another form of energy. Question is what happens to the momentum of the bicyclist mass m. Evidently it has become zero as the velocity of the mass is now is zero and the kinetic energy of the system (the bycyclist) has become heat, due to an external force (friction) acting on the system.

Evidently momentum of a system is not conserved when an outside force is allowed to affect it.

Same evidently applies to top part C of WTC 1 impacting lower part A, with part A applying big forces on C. Anyone suggesting that momentum of C then is conserved doesn't know what he is speaking about. If same person then suggests that C starts to compact A into rubble (part B) and that a one-way crush down of A is possible - due to conservation of momentum - this person just confirms the ignorance of physics shown a little earlier.

 

[Heiwa]

Heiwa,

I've got a question for you.

The concrete floors of the towers were rated to carry about 30 psf live load. Including safety factor, their design was for 100 psf max. What do you think would have happened to them if you shoveled in 300 psf of scrap metal?

According to Greg Ulrich's estimates, if the upper block is destroyed when it falls onto the lower block, the mass of the upper block amounts to about 600 psf on the 98th floor.

Even ignoring the momentum, what happens when that 600 psf of debris is piled up on the 4" thick concrete floor? It collapses.

And what happens when that 600 psf, plus the mass of the collapsed 98th floor, then fall onto the 97th floor? Even without considering momentum effects? It collapses.

What component of the floors & cross trusses do you imagine is going to support the weight of the upper block? Because that weight AIN'T going to be supported by the columns...

Tom

A floor is a secondary element of the tower structure. It (its trusses) carries load to the primary structure - the columns.
The floor is rated to carry 30 psf with a FoS 3.33, i.e. it can carry 100 psf.

If you overload the floor with say 300 psf lose items, e.g. scrap, you will locally damage it! The floor (truss) itself may break in the middle and the lose items flow down on the floor below through the opening in the floor. Or the floor may break its connection at an outside wall, floor drops down on next floor and lose items may flow out through the window there.

Evidently the columns are not damaged, when you overload a floor.

This is one reason why a one-way crush down of a structure with primary and secondary elements connected to one another cannot take place.

 

[tfk]

Anders,

I thought I made clear in post #1909 the difference between momentum and energy. Kinetic energy = momentum times velocity divided by 2. We all know that when the bicyclist, no names, just a bicyclist, with mass m drops off the bike, hits ground and friction decelerates the mass m to velocity 0, the kinetic energy is transformed into heat, which is just another form of energy. Question is what happens to the momentum of the bicyclist mass m. Evidently it has become zero as the velocity of the mass is now is zero and the kinetic energy of the system (the bycyclist) has become heat, due to an external force (friction) acting on the system.

Evidently momentum of a system is not conserved when an outside force is allowed to affect it.

Same evidently applies to top part C of WTC 1 impacting lower part A, with part A applying big forces on C. Anyone suggesting that momentum of C then is conserved doesn't know what he is speaking about. If same person then suggests that C starts to compact A into rubble (part B) and that a one-way crush down of A is possible - due to conservation of momentum - this person just confirms the ignorance of physics shown a little earlier.

.
Wow. All those words.

Hoping to bloviate away the blatant error in this statement:

... are you really sure that the momentum of the bicyclist was transferred to the Earth affecting its momentum? Maybe the momentum became heat ...?

.
After your error has been pointed out to you about 5 times.

Anders, you REALLY should stop this nonsense. It's making you look silly.

Everyone here with any tech background knows what kinetic energy & momentum are. You can stop that nonsense.

Everyone here with any tech background, except you apparently, knows exactly what happened to the bicyclist's momentum. You are the only person asking "But are you really sure that the momentum of the bicyclist was transferred to the Earth affecting its momentum?"

The answer is "yes, the momentum is transferred to the earth". And no, it did not "become heat".

Everyone here with a tech background, except you apparently, understands that momentum is NOT turned into heat. By the simple, obvious proof that VECTORS (momentum) do not turn into SCALARS (heat).

Everyone here with a tech background, apparently you apparently, understand that kinetic energy (also a scalar) gets converted into heat (another scalar). And that this process does not "absorb" or "reduce" or "remove" momentum in the slightest.

But you'll simply keep posting meaningless words after meaningless words, ad infinitum, rather than say "Ooops, I blew it".

This does not help your credibility.

Tom

 

[tfk]

A floor is a secondary element of the tower structure. It (its trusses) carries load to the primary structure - the columns.
The floor is rated to carry 30 psf with a FoS 3.33, i.e. it can carry 100 psf.

If you overload the floor with say 300 psf lose items, e.g. scrap, you will locally damage it!

.
I didn't say "overload the floor locally". I said "overload the entire floor". All of it. To about 600 psi. The answer is "the whole floor collapsed".

Related question... If the cross trusses are rated to carry 30 psi, with a FoS of 3, do you think that the brackets connecting the cross trusses to the columns would be designed with FoS of 20? If you do, you'd be wrong.

Now, what happens when the 600 psi rated loads, over the ENTIRE FLOOR, is applied to the bracket & supports that will also be rated to carry about 100 psi floor loading?

It collapses.
.

The floor (truss) itself may break in the middle and the lose items flow down on the floor below through the opening in the floor. Or the floor may break its connection at an outside wall, floor drops down on next floor and lose items may flow out through the window there.

.
To a high probability,

1. the concrete buckles & collapses at many, many locations.
2. the cross trusses do not break in the middle, but buckle in the middle.
3. when they buckle, they are pulled inward from the external columns & outward from the core columns, and fracture at one or both locations.
4. when the various cross trusses collapse, they do not "dump their contents out thru the window". This is purely ludicrous. In order to do this, the floor would still have to be intact after dropping and able of supporting the 600+ psf load. Those floors were neither intact nor able to support 600 psf.

If this idiocy were true, there would be little to no rubble WITHIN the footprint of the building. It would be left in giant rubble heaps from the edges of the building outward. Nothing like this was seen.
.

Evidently the columns are not damaged, when you overload a floor.

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Sure thing. 36' high columns that are stacked on top of each other and held together with 4 1" diameter bolts are going to be able to produce a 3, 6 or 9 story tall fence that will contain 50,000 tonnes of falling debris without bracing...

What did you say you did for a living?

Tom

 

[Tony Szamboti]

.
I didn't say "overload the floor locally". I said "overload the entire floor". All of it. To about 600 psi. The answer is "the whole floor collapsed".

Related question... If the cross trusses are rated to carry 30 psi, with a FoS of 3, do you think that the brackets connecting the cross trusses to the columns would be designed with FoS of 20? If you do, you'd be wrong.

Now, what happens when the 600 psi rated loads, over the ENTIRE FLOOR, is applied to the bracket & supports that will also be rated to carry about 100 psi floor loading?

It collapses.
.

.
To a high probability,

1. the concrete buckles & collapses at many, many locations.
2. the cross trusses do not break in the middle, but buckle in the middle.
3. when they buckle, they are pulled inward from the external columns & outward from the core columns, and fracture at one or both locations.
4. when the various cross trusses collapse, they do not "dump their contents out thru the window". This is purely ludicrous. In order to do this, the floor would still have to be intact after dropping and able of supporting the 600+ psf load. Those floors were neither intact nor able to support 600 psf.

If this idiocy were true, there would be little to no rubble WITHIN the footprint of the building. It would be left in giant rubble heaps from the edges of the building outward. Nothing like this was seen.
.

.
Sure thing. 36' high columns that are stacked on top of each other and held together with 4 1" diameter bolts are going to be able to produce a 3, 6 or 9 story tall fence that will contain 50,000 tonnes of falling debris without bracing...

What did you say you did for a living?

Tom

The floors were capable of supporting 12 times their own weight. See question 1 in the NIST Dec. 2007 FAQ.

http://wtc.nist.gov/pubs/factsheets/faqs_12_2007.htm

 

[BigAl]

A floor is a secondary element of the tower structure. It (its trusses) carries load to the primary structure - the columns.
The floor is rated to carry 30 psf with a FoS 3.33, i.e. it can carry 100 psf.

The safety factor is eaten up by truss damage caused by the airplane impact, unfought fire, and the 150 unplanned tons of aircraft debris.

 

[aggle-rithm]

I am glad that you agree that friction stops the bicyclist dropping off the bike. But are you really sure that the momentum of the bicyclist was transferred to the Earth affecting its momentum? Maybe the momentum became heat - global warming, you know?

My God....do you know what this means?

Isaac Newton was in on it!!!!

This dastardly conspiracy runs far deeper than we feared...