Elastic collision?

[Capiert]

1 hour ago, swansont said:

I don't see any explanation from you, so your optimism is unwarranted.

I guess you mean work energy WE=F*d,

 so I'm stuck with (the fact) that the defomational distance d

 done by an applied force F

 is (defined by you physicists)

 as an energy concept

 (instead of a momentum concept).

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Yes, in a subtle way that will cause issues in some problems.

Would you please give me a hint what could go wrong?

That might help me change my ways for the improvement.

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But acceptable for most cases.

Thanks.

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That's trivially true.

I would hope so.

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That would depend on the circumstance. You seem to be focused on there being one concept to apply, and that's simply shortsighted. There are a number of concepts that might apply in a physics problem. 

I search for confirmation, from several aspects,

 even though I can not deal with all aspects, that are beyond me.

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No, in fact that opposite is true. There is no inherent motion. You are free to choose any inertial reference frame,

The origin, of the big bang, seems to me the most relevant (for an underlieing inherent momentum).

Other than that, the speed of light.

Those 2, & the earth's are most relevant to me.

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and physics will work in that frame. IOW, you are free to choose a frame where you are at rest, and you are free to choose a frame in which you are moving at some constant velocity.

We generally choose the frame where the solutions are the simplest to come by.

The universe doesn't have a center.

I'll assume though, that the big bang had an origin (x,y,z=0,0,0) position.

?

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That's an incorrect summary of the big bang, but then, how did the big bang enter the conversation?

Everything moves in the universe, was my statement.

Choosing the BBT origin, was my attempt at prescribing a simple reference,

 to describe that motion easily. e.g. generally.

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We were talking about collisions.

Quite right, & the discussion was about momentum storage (instead of KE=elastic).

I.e. 1st, (so_called) static momentum must be established

 in order to discuss momentum storage.

To do that we need motion,

 but if we see no motion then we must deny momentum.

A terrible dilemma.

But if we know everything moves anyway,

 (& static is only identical speed, wrt the (same) reference)

 then the problem is solved.

What is the inherent speed of matter?

Is it light's speed c?

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The salient question is how big is it? If it's imperceptibly small, it can be ignored.

Ignorance is a continuing process.

It repeatedly pops up.

But you are right,

 we can approximate,

 for what is significant in most cases.

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In most cases, the rotation of the earth will not have any effect that you can measure.

Ok. But my question was (really more like) is the earth moving?

I.e. apparent static (=at rest) is really moving.

There is not (really) such a thing as not moving.

The earth's rotation is 1 thing,

 but our speed thru the milkyway galaxy is another!

& even there you will say that galatic_speed is not significant,

 till something happens.

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Math

Ok.

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But not all balls deform like a spring, so this is a bad assumption.

It's a simple explaination (analogy), to say it briefly.

But they will deform.

Or won't they (even though that deformation might be too small to measure)?

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To assume deformation like that is to assume that energy is conserved, because an ideal spring is a device that conserves mechanical energy.

Work energy WE=F*d.

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Yes. You want to assume mechanical energy is conserved but do it in a way that doesn't directly invoke the conservation. But that doesn't mean you aren't using the concept.

Now I recognize, that you have been using that WE formula, as your premise,

 because it is (previously) defined in physics (as your rights, to catalog so).

I had no idea (how you were thinking) before that. 

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IOW, you can't assume the collision is elastic, because "elastic" and "conservation of KE" are equivalent statements,

Don't you mean KE=WE elastic, instead?

E.g. KE=WE=KE'. Prime ' is for after the collision.

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and you said you could do this without invoking energy concepts, as you don't trust them.

Yes, it seems so. I did not recognize that the WE equation('s distance d) was (strictly, only in) an energy equation,

 after I had used it for my derivations.

Mistakes happen. Please forgive. (Humble, humble).

 

Momentum wise I would need (some kind of) a rooted_distance, instead.

(Or am I still wrong, on that 1, too?)

 

Edited September 4, 2018 by Capiert

[swansont]

53 minutes ago, Capiert said:

I guess you mean work energy WE=F*d,

We were talking about your phrase "stored momentum" and all I've done is ask you what you meant by that, so how did we get from me asking you for clarification to what I mean? I want YOU to explain what YOU mean by that phrase.

53 minutes ago, Capiert said:

 so I'm stuck with (the fact) that the defomational distance d

 done by an applied force F

 is (defined by you physicists)

 as an energy concept

 (instead of a momentum concept).

Yes. Because in a typical collision, momentum will be conserved, as there is no net external force. It tells you nothing about whether KE is conserved. 

53 minutes ago, Capiert said:

Would you please give me a hint what could go wrong?

You are not using differentials, which means you are basically using average values. That's fine if the force is constant in time. If the force is changing with time, the equations will not be accurate.

53 minutes ago, Capiert said:

 Everything moves in the universe, was my statement.

What is your speed right now?

Motion is relative.

53 minutes ago, Capiert said:

 Quite right, & the discussion was about momentum storage (instead of KE=elastic).

I.e. 1st, (so_called) static momentum must be established

 in order to discuss momentum storage.

To do that we need motion,

 but if we see no motion then we must deny momentum.

A terrible dilemma.

Only if you want to advance the notion of stored momentum and inherent motion; the latter was discarded more than 100 years ago. I don't know if the former was ever a thing. 

53 minutes ago, Capiert said:

But if we know everything moves anyway,

 (& static is only identical speed, wrt the (same) reference)

 then the problem is solved.

What is the inherent speed of matter?

Is it light's speed c?

There is no such thing as an inherent speed of matter.That's one conceptual failure. And conjecture that it's c brings another conceptual failure to the table, since matter can never move at c.

53 minutes ago, Capiert said:

 Ok. But my question was (really more like) is the earth moving?

I.e. apparent static (=at rest) is really moving.

There is not (really) such a thing as not moving.

The earth's rotation is 1 thing,

 but our speed thru the milkyway galaxy is another!

& even there you will say that galatic_speed is not significant,

 till something happens.

Does the earth's rotation, revolution about the sun or the solar systems orbit about the galactic center affect how you approach a problem of two balls colliding on a billiards table?

53 minutes ago, Capiert said:

 

Ok.

It's a simple explaination (analogy), to say it briefly.

But they will deform.

Or won't they (even though that deformation might be too small to measure)?

Work energy WE=F*d.

And what if the deformation remains?

53 minutes ago, Capiert said:

 Yes, it seems so. I did not recognize that the WE equation('s distance d) was (strictly, only in) an energy equation,

 after I had used it for my derivations.

Mistakes happen. Please forgive. (Humble, humble).

The E stands for energy, does it not?

53 minutes ago, Capiert said:

Momentum wise I would need (some kind of) a rooted_distance, instead.

(Or am I still wrong, on that 1, too?)

I don't see how it's going to matter, since conservation of momentum will still hold regardless of whether mechanical energy is.

[Capiert]

11 hours ago, swansont said:

We were talking about your phrase "stored momentum" and all I've done is ask you what you meant by that, so how did we get from me asking you for clarification to what I mean? I want YOU to explain what YOU mean by that phrase.

"optimism" denied.

Because I had not recognized you were impling WE=F*d is elastic;

 instead of stored momentum

 might be the (2*a*d)^0.5 part

 of the momentum

mom=m*(((vi^2)+2*d*a)^0.5)-vi.?

Sorry, (it's vague, general) typo, reminder.

That comment is (awkwardly) in the wrong place.

Is that a bit better?

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Yes. Because in a typical collision, momentum will be conserved, as there is no net external force. It tells you nothing about whether KE is conserved. 

So momentum is the unlieing (basis) principle for collision.?

For all collisions (non_elastic, partialy elastic, & totally elastic)?

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You are not using differentials, which means you are basically using average values. That's fine if the force is constant in time. If the force is changing with time, the equations will not be accurate.

Which means we need to integrate then?

But does that work well for (all) non_linear accelerations?

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What is your speed right now?

I think it is zero wrt to my (immediate) surroundings (on earth),

 but I know I'm moving fast (eastwards) as the earth rotates thru the day.

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Motion is relative.

Yes, but our (so_called static) immediate surroundings are a deception.

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Only if you want to advance the notion of stored momentum and inherent motion; the latter was discarded more than 100 years ago. I don't know if the former was ever a thing. 

You know the earth is rotating,

 with no motion you are claiming identical speed,

 an inherent motion (i.e. speed) must exist

 (if we automatically imply (identical) speed).

The real question is which (moving) reference to choose,

 to quantify (how fast).

No motion is (truely) absurd.

All things are moving (in the universe. Thus inherent motion exists.)

Or isn't it?

(I doubt that you can convince me otherwise. If you're clever enough you might. I don't know the outcome.

But as the wording stands, it makes no sense otherwise (to me). & it's Newtonian.)

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There is no such thing as an inherent speed of matter.

Then nothing is moving.?

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That's one conceptual failure.

That's not a conceptual failure, it's a fact; or else bad wording.?

Everything in this universe moves although we can not say an independent speed wrt no reference.

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And conjecture that it's c brings another conceptual failure to the table, since matter can never move at c.

Wrt light we are moving at -c.

I do not see an error. Einstein said there is no preferred reference, they all work well.

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Does the earth's rotation, revolution about the sun or the solar systems orbit about the galactic center affect how you approach a problem of two balls colliding on a billiards table?

You're right, they do not produce a difference,

 so that is the marvelous advantage

 when studying (=observing) collisions;

 until we get down to atoms & sub_atomic particles

 where the music changes (becoming significant).

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And what if the deformation remains?

Then it is a non_elastic collision; or else a partially elastic collision.

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The E stands for energy, does it not?

Yes. I did not convert after deriving

 (probably assuming (the momentum energy relation mom=E/va is so obvious) I could, later;

 & forgot that it (the existing work_energy formula) still was energy).

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I don't see how it's going to matter, since conservation of momentum will still hold regardless of whether mechanical energy is.

It would matter for your challenge, if I had a momentum equivalent for your (physicist's) WE.

Or wouldn't?

 

Edited September 5, 2018 by Capiert

[swansont]

4 hours ago, Capiert said:

"optimism" denied.

Because I had not recognized you were impling WE=F*d is elastic;

I'm not implying that. W = F*d applies to many cases, and is not specific to elastic collisions.

4 hours ago, Capiert said:

 instead of stored momentum

Which you STILL have not explained in any detail

4 hours ago, Capiert said:

 might be the (2*a*d)^0.5 part

 of the momentum

mom=m*(((vi^2)+2*d*a)^0.5)-vi.?

I don't recognize that equation. Partly because it can't be correct. (you are subtracting a speed from a momentum)

4 hours ago, Capiert said:

 So momentum is the unlieing (basis) principle for collision.?

For all collisions (non_elastic, partialy elastic, & totally elastic)?

Collisions generally occur such that there is no net external force on them, so momentum will be conserved. So you can apply that to the problem.

4 hours ago, Capiert said:

Which means we need to integrate then?

But does that work well for (all) non_linear accelerations?

Yes.

4 hours ago, Capiert said:

I think it is zero wrt to my (immediate) surroundings (on earth),

 but I know I'm moving fast (eastwards) as the earth rotates thru the day.

Does your motion to the east matter in many cases? Do you drove slower when going to the east, and faster to the west, owing to the earth's rotation? If you toss a brick 1m in the air, do you have to worry about the earth's rotation?

4 hours ago, Capiert said:

Yes, but our (so_called static) immediate surroundings are a deception.

Deceptive perhaps. But also inconsequential in most cases.

4 hours ago, Capiert said:

You know the earth is rotating,

 with no motion you are claiming identical speed,

If you are standing still, you have an identical speed to a tree or rock. Your motion to them is relative. You are not moving relative to the tree or rock. The motion of the earth doesn't matter.

4 hours ago, Capiert said:

 an inherent motion (i.e. speed) must exist

Which keep insisting, but with no basis or support.

4 hours ago, Capiert said:

 (if we automatically imply (identical) speed).

The real question is which (moving) reference to choose,

 to quantify (how fast).

Yes, which reference to choose. But that's not consistent with your claim. If motion is inherent, we have no choice in the reference. We must choose the one frame where we could possibly be at rest. Furthermore, we must be able to tell we are moving with respect to that frame.

4 hours ago, Capiert said:

No motion is (truely) absurd.

Indeed. But who is claiming there is no motion?

No relative motion, on the other hand, is trivial.

4 hours ago, Capiert said:

All things are moving (in the universe. Thus inherent motion exists.)

Nope. 

4 hours ago, Capiert said:

 Then nothing is moving.?

The problem is that this statement is not the same as saying that there is no such thing as inherent motion.

4 hours ago, Capiert said:

That's not a conceptual failure, it's a fact; or else bad wording.?

Yes. You fail to grasp the notion that motion is relative rather than absolute.

4 hours ago, Capiert said:

Everything in this universe moves although we can not say an independent speed wrt no reference.

But what if we choose a reference that is fixed with respect to us? We would not be moving relative to that. The tree or rock.

4 hours ago, Capiert said:

Wrt light we are moving at -c.

Light moves a c relative to us. We can't say we are moving relative to light, because light has no inertial reference frame.

4 hours ago, Capiert said:

I do not see an error. Einstein said there is no preferred reference, they all work well.

And you are saying that there is inherent motion. 

4 hours ago, Capiert said:

 Then it is a non_elastic collision; or else a partially elastic collision.

Which is a designation we make based on whether or not kinetic energy is conserved. 

4 hours ago, Capiert said:

 It would matter for your challenge, if I had a momentum equivalent for your (physicist's) WE.

Or wouldn't?

But you can't from momentum to that point, unless you are applying some aspect of work and/or energy.