The Line

[aquatus1]

In this hypothetical, or whatever it is properly called, is one allowed to examine the big picture? Is one allowed to examine the forensics involved with whatever the result of floor failure turns out to be?

There are plenty of threads where people can pretend to understand what forensic evidence is and how to analyze it. This thread is for the simpler, foundational aspects, that are often ignored while looking at the "big picture". It isn't so much a hypothetical, as a primer in the basic academic aspects of physics and critical thinking.

[aquatus1]

I'll try again, this time explaining what should have been self evident.

If it had been self-evident, there wouldn't need to be a thread specifically for people to show their work now, would there?

Be snarky somewhere else. In this thread, support yourself or beat it.

"we get a downward force of 23,104N vs. an upward force of 3960N, which results in a downward force of 19,144N"

this is incorrect.

newtons third law says "When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction to that of the first body."

so, if the top block hits the bottom block with a force of 23,104 N, then newtons third law says that the bottom block will also exert an upwards force of 23,104N on the top block.

Technically, yes, however the entire purpose of this example is to show the compounding increase of energy achieved by a falling object as opposed to one at rest. Newton's 1st Law is about balanced forces, such as forces at rest. Newton's 3rd Law is about forces interacting. Newton's 2nd Law, however, is about forces which are unbalanced, such as collisions and impacts, which is what we are dealing with.

So, what I am attempting to show in this example, is that a slab of concrete that exerts X amount of force while at rest (while simultaneously receiving X amount of force from the slab it is resting on, as per Newton's 3rd), is going to gain dramatic amounts of energy after falling (acceleration due to gravity). At the moment that these two slabs contact (interact), the bottom slab (which was pushing upwards with X amount of force) is now being pushed downwards with a slab that has X times 5, 10, 15 times as much force as before. Sure, it can try to push back with the same amount of force, but whether or not it actually succeeds in doing so is another question altogether.

By sheer definition, Newton's 3rd law tells us that if an object is at rest (equilibrium) in one position, adding energy to that object automatically creates a state of imbalance, which requires us to use Newton's 2nd law. The Potential Energy of an object and the Kinetic Energy of an object remains the same, and the force of both slabs pushing against each other at equilibrium are equal, however the addition of the energy gained due to gravitational acceleration adds extra energy to the top slab, and has to be factored in.

my reading is that aquatus is trying to show that the wtc north tower could have collapsed without the aid of demolition devices.

Not at all. That's too big picture. At this level, all I am trying to do is to give people an idea of just how much energy we are dealing with here. It is my hope that when people notice how ludicrously, ridiculously, large the differences in forces are, they will be able to, all on their own, decide whether or not the conspiracy arguments are valid or merit credibility.

he has started with a model of floor slabs suspended in air like magic carpets. this alone invalidates any conclusion since it is the columns/walls that hold up a building.

What supports the slabs is irrelevant. The only thing that matters is that they were supported with X amount of force, pushing upwards to match the X amount of force pushing downwards. What the material was, what the configuration was, none of that is relevant to the equations of force, which is the only thing that is being discussed in this example.

storey 1 needs to resist the weight of all storeys above it, but in aquatus model, storey one is only resisting the weight of 2 storeys. so the model fails there as well.

If you are not going to bother going paying attention to the example, do not bother posting about it.

I made it very clear that each floor was being given the appropriate multiple of force. Floor 5 was pushing up with the force required to match 2 slabs, Floor 4 was pushing up with the force to match 3 slabs, Floor 3 was pushing up to match the force of 4 slabs, and so on.

I also showed how Floor 5 was struck with a force equivalent to more than 5 slabs, Floor 4 was struck with equivalent of more than 13 slabs, Floor 3 by the force of more than 264 slabs, and so on.

It is this unbelievable multiplication of forces involved that I want people to wrap their heads around. It is the sheer absurdity of the quantities of energy produced that I believe will make people look at many conspiracy arguments and go "Oh...well, yeah, that's kind of silly, now that we look at it this way."

err...the basics of science - an experiment.

If we were actually producing experiments or evidence, sure. Being that we are simply discussing a set of mathematical equations derived from Newton's Laws of Motion, well, I'm sure Youtube has plenty of videos of teachers swinging bowling balls at their student's noses and such.

can you explain why the experiments in the video did not completely destroy the structures.

Yes, I can, but I want an acknowledgement from you that you understand the academic side of it first. I have no intention of arguing the validity of Newtons Laws of Motion. If you do not understand some aspect of it, I will be more than happy to explain that as well, but if you do not understand the foundation of an experiment, you will not understand the experiment either, no matter how much you think that you do.

[Stellar]

Just pointing something out, because the physics I'm seeing people argue here is horrendous:

The force opposite to the floors falling due to gravity is the Earth getting pulled up to the floors that are falling... now continue.

[aquatus1]

Just pointing something out, because the physics I'm seeing people argue here is horrendous:

The force opposite to the floors falling due to gravity is the Earth getting pulled up to the floors that are falling... now continue.

Oh, that is going to blow some minds!

Incidentally, in response to my own question:

"Did anyone notice what I omitted from the above example, where 1 floor devastated the 5 floors below it?"

The correct answer is this:

Floor 7.

Yep. All those crazy numbers?

The actual results are much, much bigger.

By the way, I am going to double-check my maths and clean it up a little, but as has been pointed out, this is not something that is either directly applicable to real world situations, or which, in and of itself, will invalidate any specific conspiracy theory. It is my hope, however, that it will provide a much needed sense of proportion to some of the outlandish claims one does see being spread.

[shrooma]

It is my hope, however, that it will provide a much needed sense of proportion to some of the outlandish claims one does see being spread.

.

you'd probably be better off with napalm.

lots & lots of napalm.

;-)

[shrooma]

Just pointing something out, because the physics I'm seeing people argue here is horrendous:

The force opposite to the floors falling due to gravity is the Earth getting pulled up to the floors that are falling... now continue.

.

opposite force, yes, but wouldn't an applied force only count if the two were in contact?

[Stellar]

And if you want to draw a force diagram showing all the complementary forces in this instance, it'll get quite complex and messy, since you can always make it "more complex". Realistically, you do not need to even consider Newton's 3rd law in this instance since what matters is how much force is getting applied vs how much force it can hold.

The frame of the building can only hold so much force before breaking. When an object suddenly impacts another object, it transfers some energy to it. In other words, the object getting impacted slows down (decelerates) the impacting object. This can cause the force to be *much* greater at the instant of impact.

Back to the example of the scale. When you stand on the scale, it gives you a certain reading. This reading is proportional (dependent) on your mass in the presence of gravitational acceleration (F=mg). If you were to fall from 10 meters onto the scale and impacted the scale with a velocity of 18.6 m/s, what would happen? You would be essentially instantaneously stopped. Brought back to a speed of 0. For ease of simplifying the math, lets say that it actually took 1 second for the scale to slow you down (a huge simplification). That means you were accelerated at a rate of 18.6 m/s/s in the opposite direction to your fall. Hence, your scale would show a reading proportional to F=m*18.6 or, in other words, F=2mg. So, for that 1 second, your scale would read more than your actual weight, until everything came to rest.

In the example above, if we were to draw a free-body diagram with the complementary forces as per Newtons 3rd law, what would we see? Well, initially, we'd have a force pointing downwards applied to the falling person, and an equal force pointing upwards applied to the Earth. During impact, we would have a force peaking at F=m*18.6 pointing up on the person and the same force pointing down on the scale/Earth until it came to rest, at which point you would have the an upwards force equivalent to F=(mperson + mscale)g on the person, and that same force pushing down on the scale/earth.

You would also, throughout, have the gravitational force of the scale pushing down on the scale and up on the Earth.

Thats the scenario in a nutshell.

[Stellar]

.

opposite force, yes, but wouldn't an applied force only count if the two were in contact?

I'm not sure I know what you mean by "count". An opposite and equal force is *always* present. All that this means is that you dont have one object that's fixed. Both move. When the Earth's gravity pulls an apple down towards the Earth, it also pulls the Earth towards the apple. The only reason we don't "notice" this is because the mass of the apple is so small compared to the mass of the Earth, which means that the apple will accelerate and move at a faster speed than the Earth, which will accelerate so slowly its essentially negligible.

[flyingswan]

I'm not sure I know what you mean by "count". An opposite and equal force is *always* present.

The forces are only equal if the objects are in contact. After the initial drop, there is a growing layer of crushed floors between the upper and lower blocks. This layer is falling, like the upper block. This means that the situation is no longer symmetrical between the two blocks. The force on the lower block is greater than the force on the upper block by the amount of the force on the layer of crushed floors.

The force on the lower block is resisting the fall of both the upper block and the crushed layer. The force on the upper block is just resisting the fall of the upper block itself.

Edited May 29, 2013 by flyingswan

[Stellar]

The forces are only equal if the objects are in contact.

No, you are wrong. The forces Newtons 3rd law talks about are always equal, regardless of whether they are in contact or not.

After the initial drop, there is a growing layer of crushed floors between the upper and lower blocks. This layer is falling, like the upper block. This means that the situation is no longer symmetrical between the two blocks. The force on the lower block is greater than the force on the upper block by the amount of the force on the layer of crushed floors.

The force on the lower block is resisting the fall of both the upper block and the crushed layer. The force on the upper block is just resisting the fall of the upper block itself.

You are correct here, but the forces you speak of here are not the forces that Newton's 3rd law refers to.

[Little Fish]

Be snarky somewhere else. In this thread, support yourself or beat it.

as per newtons third law, my snarky is only a response to someone else's snarky.

Technically, yes, however the entire purpose of this example is to show the compounding increase of energy achieved by a falling object as opposed to one at rest. Newton's 1st Law is about balanced forces, such as forces at rest. Newton's 3rd Law is about forces interacting. Newton's 2nd Law, however, is about forces which are unbalanced, such as collisions and impacts, which is what we are dealing with.

So, what I am attempting to show in this example, is that a slab of concrete that exerts X amount of force while at rest (while simultaneously receiving X amount of force from the slab it is resting on, as per Newton's 3rd), is going to gain dramatic amounts of energy after falling (acceleration due to gravity). At the moment that these two slabs contact (interact), the bottom slab (which was pushing upwards with X amount of force) is now being pushed downwards with a slab that has X times 5, 10, 15 times as much force as before. Sure, it can try to push back with the same amount of force, but whether or not it actually succeeds in doing so is another question altogether.

the bolded bit is incorrect as per newtons third law. it does not "try to push back with the same amount of force" nor is there a question of whether it succeeds or not in exerting the force - it DOES push back with same force. if the falling slab impacts the stationary slab with say, a force of ten billion trillion newtons, then the stationary slab will exert the same ten billion trillion newtons on the impacting slab. this is an important concept to acknowledge because you are implying that the stationary slab will be the only slab that fails (breaks), when in fact both impactor and impactee will fail (break). if you are thinking that only the impactee will fail then your model is analogous to a steel slab falling on glass slabs. again this is important since the 10 storey falling block of wtc1 will be destroyed after the first 10 "floor impacts", leaving 90 intact storeys vs 20 fragmented storeys which is a different problem altogether (less than 20 actually since a lot of debris is not going to do any impacting).

I want an acknowledgement from you that you understand the academic side of it first.

yes i understand simple physics, how about you? do you understand that two objects impacting will exert the same force on each other at the same instant? Edited May 29, 2013 by Little Fish

[Little Fish]

Force=Mass x Acceleration.

gravity & acceleration are both interchangeable and indestinguishable from each other.

a 50kg object at rest doesn't have the same mass characteristic as an accelerating 50kg object, which is why aquatos made the analogy of a weight at rest and an accelerating body. so your saying that gravity acting on mass as a constant is wrong. that's why you experience accelerative g-forces, not because you've suddenly become heavier, but because you've gained energy, E=Mc2 remember. the more energetic, the more mass, which is why only massless bodies can achieve light-speed, because the faster something is moving, the more massive it becomes.

i have no idea what you are trying to say. and i did not say the bolded bit. i said gravity was constant in the context of the discussion.

"you can't properly apply newton's third law to the problem of the collapsing floor due to momentum."

newton's third law is a law. you don't get to pick and choose when it applies. it applies because it is a law. however, on its own it doesn't determine what happens to the motion after collision.

"the floor underneath the collapsing floor may respond with an equal force"

there is no "may", it does as per newtons third law. a law of physics cannot be broken.

"but as the floor underneath's collapse point is well below the force being applied, there is no way for it to be sustained, so it WILL collapse."

whether it collapses or not does not negate that the stationary slab exerts the same force on the impacting slab.

do not assume that i mean to say it will not collapse- i did not say that.

[aquatus1]

as per newtons third law, my snarky is only a response to someone else's snarky.

I don't care who's snark it is. If you haven't supported your claim, you don't get to snark.

the bolded bit is incorrect as per newtons third law.

No, there is no conflict with Newtons 3rd law. I can't completely understand what you think the purpose of the 3rd law is.

it does not "try to push back with the same amount of force" nor is there a question of whether it succeeds or not in exerting the force - it DOES push back with same force.

Yes, it does, to the extent that it has force to push back with. Once the opposite forces have been equally matched, the objects come to rest. If, however, there is still energy left over, that energy will force continued movement until such time that it finds equilibrium as well. Whether you like it or not, the 3rd law is about interactions. Its purpose is to define (for lack of a better word) the two forces that are interacting; it forbids the existence of a single force. The 3rd law does not deal with the force and acceleration of a single object, unlike the 1st Law. It deals with the net result of the forces involved, the action and reaction of the objects.

Newton's 3rd Law is less a law and more a description of forces interacting.

The smaller force does not magically generate more energy out of nowhere. Force is a variable used to calculate interactions between objects based on their mass and velocity. It doesn't reflect any particular quality of whatever example we use. We can put a jeep on top of a grape and claim that the forces are equal and opposite, but that doesn't mean that grapes have the power to hold up jeeps. Once the upward force of the grape is matched by the downward force of the jeep, the jeep still has plenty of energy left to keep moving downward, thanks to gravity. If, however, we place the grape on top of the jeep, even though gravity is giving the grape extra force, it still doesn't have enough force to move the jeep.

if the falling slab impacts the stationary slab with say, a force of ten billion trillion newtons, then the stationary slab will exert the same ten billion trillion newtons on the impacting slab.

Only in the sense that the net force between the two objects is equal and opposite. In other words, the impacting slab is being pulled towards the stationary slab with ten billion trillion newtons of force, and the stationary slab is being pulled towards the impacting slab with ten billion trillion newtons of force, as per 3rd law, however, when contact occurs, we have to determine the

this is an important concept to acknowledge because you are implying that the stationary slab will be the only slab that fails (breaks), when in fact both impactor and impactee will fail (break).

How am I implying that when I specifically removed energy at every interaction? I gave the falling mass a "bounce. I calculated the reduction in speed of the falling mass due to the impact.

And there is no "breaking" involved here. Two objects, two movements, one with a logarithmically growing increase in energy, and one with a mathematical increase in energy. Two forces impact, the smaller force cancels itself out on the larger force, and the remaining force continues in the path it was taking before being interrupted. Just because the direction they are taking is "down" (because, you know, gravity), doesn't change those characteristics. If this was in space and we were talking about a rocket accelerating towards some stationary satellite, the same would apply.

if you are thinking that only the impactee will fail then your model is analogous to a steel slab falling on glass slabs.

There is nothing in these formulas that reflects different properties of the objects involved.

again this is important since the 10 storey falling block of wtc1 will be destroyed after the first 10 "floor impacts", leaving 90 intact storeys vs 20 fragmented storeys which is a different problem altogether (less than 20 actually since a lot of debris is not going to do any impacting).

That is a different argument altogether, and not the one I was demonstrating. If you wish to discuss that scenario, I will be more than happy to, however, first let's finish the example that is actually on the table.

Don't change the variables randomly and then argue the results of the original are wrong.

yes i understand simple physics, how about you? do you understand that two objects impacting will exert the same force on each other at the same instant?

Do you understand that Newton's 3rd Law is not an iron rule dictating that all forces interacting with each other are magically equal, but rather that its purpose is to define the net forces involved? In other words, that the energy due to momentum in each body will be retained in one way or another, not that the energy of each body is inherently equal?

[aquatus1]

After the initial drop, there is a growing layer of crushed floors between the upper and lower blocks. This layer is falling, like the upper block. This means that the situation is no longer symmetrical between the two blocks. The force on the lower block is greater than the force on the upper block by the amount of the force on the layer of crushed floors.

The force on the lower block is resisting the fall of both the upper block and the crushed layer. The force on the upper block is just resisting the fall of the upper block itself.

This is more a question of elastic vs inelastic collisions. In the example I have presented, I am using a combination of both depending on which system I am calculating. As I mentioned before, this is a simple example to demonstrate one single aspect of physics, that of the logarythmic increase of energy due to gravity.

The thing about the actual WTC collapse (or, for that matter, any collapse) is than an avalnche situation does not readily lend itself to simple physics. There are both elastic and inelastic collisions, there are unusual gravitational effects in play, the main body alternates between acting as a solid and acting as a fluid, and mass is alternately gained and lost, affecting momentum in both negative and positive ways.

Avalanches are, basically, every aspect of mechanical physics jumbled up into one chaotic package. Unfortunately, there is a lot of confusion from people who don't recognize how many different types of forces are at work here, and how things that seem like they are common sense change when physics go wild.

For instance, there are people talking about air friction acting as a cushion, or at least a significant variable of some kind. As it turns out, in avalanche scenarios, air can act as a cushion (absorbing energy), as a lubricant (increasing energy), and it can even act as a multiplier of mass!

[+Liquid Gardens]

again this is important since the 10 storey falling block of wtc1 will be destroyed after the first 10 "floor impacts", leaving 90 intact storeys vs 20 fragmented storeys which is a different problem altogether (less than 20 actually since a lot of debris is not going to do any impacting).

Why do you think this, that the damage will be equal beyond the first impact between the blocks, what happened to the mass of the crushed stories in between? Isn't it exerting a force/have energy that the remaining lower block must withstand but not the remaining upper block?

[Little Fish]

Why do you think this, that the damage will be equal beyond the first impact between the blocks

because every experiment i have seen shows it, that's why i think it.

why do you believe what you believe? show me one experiment that shows an object can crush another identical object and survive without suffering the same damage that it inflicted, or better still, an experiment to show an object crushing 10 identical objects.

"what happened to the mass of the crushed stories in between?"

it's still there, some will be between the two rigid blocks, some will freefall off the sides and some will be freefalling between the blocks.

"Isn't it exerting a force/have energy that the remaining lower block must withstand but not the remaining upper block?"

the notion that the upper 9 storey block is just freefalling whilst only the loose crushed material of 2 storeys is compressing the 99 storeys below is silly on its face, if you are trying to say that only the crushed material from the first impact is crushing the rest of the building, then you are claiming that the collapse of just the top storey (floor 110) would crush the entire building, so in order to demolish the entire wtc tower, it would be enough to just blow up the top floor (floor 110) and the resultant rubble would crush the entire building, i'm sure you'll agree that is absurd.

[Little Fish]

Force is a variable used to calculate interactions between objects based on their mass and velocity

you are confusing momentum with force.

force = mass x acceleration

momentum = mass x velocity

[Little Fish]

Newton's 3rd Law is not an iron rule dictating that all forces interacting with each other are magically equal,

I never stated that, but it is an iron rule that 2 colliding bodies exert the same force on each other.

"but rather that its purpose is to define the net forces involved?"

no, newton's third law is not that, nor does it have a purpose, it just is.

"In other words, that the energy due to momentum in each body will be retained in one way or another, not that the energy of each body is inherently equal?"

not sure what you are getting at. conservation of momentum determines the motion after collision, is that what you are getting at?

[+Liquid Gardens]

"what happened to the mass of the crushed stories in between?"

it's still there, some will be between the two rigid blocks, some will freefall off the sides and some will be freefalling between the blocks.

"Isn't it exerting a force/have energy that the remaining lower block must withstand but not the remaining upper block?"

the notion that the upper 9 storey block is just freefalling whilst only the loose crushed material of 2 storeys is compressing the 99 storeys below is silly on its face, if you are trying to say that only the crushed material from the first impact is crushing the rest of the building, then you are claiming that the collapse of just the top storey (floor 110) would crush the entire building, so in order to demolish the entire wtc tower, it would be enough to just blow up the top floor (floor 110) and the resultant rubble would crush the entire building, i'm sure you'll agree that is absurd.

You kinda dodged the second question above; although I agree that the notions you are talking about above are absurd, it doesn't have anything to do with anything I said. If some of the mass of the crushed stories, which is constantly growing as the collapse continues, is freefalling as you admit, then the answer to my question is obviously yes, the remaining intact lower block has to withstand a force, that provided by the mass of the falling middle crushed stories, that the upper block does not. Thus the forces on the intact lower block and the intact upper block cannot be equal past the first collision, in general. So then it follows that the resultant damage from these forces, in general, should not be expected to be the same on the lower block and the upper block as the forces are not equal at those two separate points. Thus, I don't know why you think the damage would be equal and that a failing floor in the lower block, after the first stories have been crushed, must also result in a crushed floor in the upper block.

[flyingswan]

No, you are wrong. The forces Newtons 3rd law talks about are always equal, regardless of whether they are in contact or not.

Oh dear me, what an admission. You have no idea at all, do you?

Unless you are considering forces that operate at a distance, like gravity, the "equal and opposite" forces only apply at the point of contact of the two bodies. If the bodies are not in contact with each other directly, but only through a third object, then you have two separate situations, two pairs of equal and opposite forces, and these two pairs are not equal to each other. If you have three blocks stacked in a vertical column, do you really think that the force between the middle and bottom block is the same as the force between the middle and top block?

[Stellar]

Oh dear me, what an admission. You have no idea at all, do you?

Unless you are considering forces that operate at a distance, like gravity, the "equal and opposite" forces only apply at the point of contact of the two bodies. If the bodies are not in contact with each other directly, but only through a third object, then you have two separate situations, two pairs of equal and opposite forces, and these two pairs are not equal to each other. If you have three blocks stacked in a vertical column, do you really think that the force between the middle and bottom block is the same as the force between the middle and top block?

Of course Im considering forces that operate at a distance. I clearly said that Newton's third law applies to all forces, regardless of whether they are in contact or not. Do you disagree with this? That is all I was saying. Of course the force on the bottom block would be greater than on the middle block! I never denied this.

[aquatus1]

you are confusing momentum with force.

force = mass x acceleration

momentum = mass x velocity

Momentum is a force, but not all forces are due to momentum.

I never stated that, but it is an iron rule that 2 colliding bodies exert the same force on each other.

I...think I am starting to see where your confusion is coming from...

"but rather that its purpose is to define the net forces involved?"

no, newton's third law is not that, nor does it have a purpose, it just is.

It just...is?

Physics isn't a belief system. Newton's Laws are not postulates. Equations and Laws are not created on a whim or exist just for the heck of it. If an equation or law is part of our system of calculation, then it has a purpose, and that purpose, just like that of any scientific theory, is to provide an explanation for a given phenomena. This is the difference between reciting what one is taught, and understanding what one is taught.

In the case of Newton's 3rd law, the purpose of the 3rd law is to describe the interactions between two objects through the calculation of the net forces within those objects.

"In other words, that the energy due to momentum in each body will be retained in one way or another, not that the energy of each body is inherently equal?"

not sure what you are getting at. conservation of momentum determines the motion after collision, is that what you are getting at?

Here is where I think your confusion is coming from.

Earlier, you have been saying that the force of the falling slab and the force of the resting slab must be equal due to the 3rd law, and you stated that you believe this because the 3rd law states "When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction to that of the first body." You have also, in later posts, continued with the notion that the bottom slab must push up with the same force as it is pushing down, and that the energy contained in 10 slabs falling will eventually be equaled by 10 slabs resting.

In other words, in all of your posts so far, you are treating the "force" in your definition of the 3rd law, as if it was energy, and as if the 3rd law was a descriptor of the quantity of energy in an object. This would also explain why your understanding of the 3rd law seems to come to a sudden halt, where once you have defined it as a postulate, there is no need to determine its purpose.

That is where the mistake is. Instead of imagining force as a quantity, imagine it as a behaviour. Try defining the 3rd law in this manner:

"Every action has an equal and opposite reaction"

It is the same statement, and a commonly used alternative definition, and the reason why it is so much more common than the original wording (Lex III: Actioni contrariam semper et æqualem esse reactionem: sive corporum duorum actiones in se mutuo semper esse æquales et in partes contrarias dirigi.) is because it focuses on the purpose of the law, which is to describe the action and reaction of two forces interacting.

If we have two objects, each one has a given amount of force, depending on all the variables we calculated using the 1st and 2nd law. When they interact, particularly in the case of collisions, they have an equal and opposite reaction to each other, but the energy within each object does not transmit to the other, nor does it either magnify or disappear.

In other words, the behaviour is equal and opposite, but the energy remains constant within each object.

This is why Newton's Laws, as fantastic a foundation for mechanical physics as they are, are too simple to describe forces when dealing with elastic or inelastic collisions, and why other mathematicians had to develop further laws and equations. It is also why it doesn't matter what is holding the slabs of concrete up; Newton's laws don't care about how a force comes about, just that the force exists, regardless of the form or makeup of the object containing the force.

But the focus of the 3rd law is behaviour, and so when we have two forces meeting, their behaviour is going to be determined by calculating the net force after impact. The equal and opposite reaction refers to the movement, momentum, direction, what-have-you, of the objects individually in regards to each other; it does not refer to the quantity of energy within each object individually.

In the classic pool experiment, the cue ball strikes a number ball and both balls collide and deflect off each other (Elastic Collision). The behaviour of each ball, the direction, angle, etc, is equal and opposite to the the other, however, the energy of each ball, depending on the initial velocity, the spin, the felt, etc, is individual to each ball. If, on the other hand, we fling two balls of clay at each other, the balls will collide and merge together (Inelastic Collision), each one loosing a little bit of energy to deformation, however the resulting mass will continue in whatever direction the remaining force was heading (momentum), with the corresponding loss in velocity.

It is an incorrect understanding of Newton's 3rd Law to state that a falling slab with 1000N of energy colliding with a resting slab with 100N will nonetheless exert an equal amount of force on each other. It simply doesn't make sense, and the reason it doesn't make sense is because Newton's 3rd is not talking about force as the quantity of energy, but rather about the behaviour of force, about how one force will react (equal and opposite reaction) to the other force.

Is that clearer?

[Likely Guy]

aquatus1,

Your argument is brilliant but, for me to believe you I need some colorful charts and graphs, a cgi simulation... OH! ...and a youtube link would be most conclusive.

No, seriously! From what I have learned, you have a pretty strong grasp of the concept of Newton's laws and you're doing a good job at relating them.

Real science cannot lie.

*thumbs up*

[aquatus1]

[Czero 101]

* Snipped for brevity *

Is that clearer?

Brilliant...

Cz