# Collision Theory

1. Dec 5, 2006

### MHefny

Can we say that the following is a theory:

If A SOLID OBJECT THAT IS NEITHER ELASTIC NOR PLASTIC
– ACCEPTS NO DEFORMATION- COLLIDES WITH ANY OTHER OBJECT
-THAT IS UNBREAKABLE -. THE SOLID OBJECT WILL STOP REGARDLESS OF ITS MASS OR VELOCITY.

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I made a simple simulator program for the spring model stated in teh document and it gave the classical correct results.

Could someone help me in validating this topic?

Thanks

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2. Dec 5, 2006

### Jheriko

This seems to disagree with conservation of momentum. If a solid object hits another solid object and comes to a complete standstill where does the momentum go if not into the other object.

From the "moving" object's perspective it as is if it is stationary and being hit by the other ball (Gallilean relativity), so we know that they can not both remain perfectly still otherwise conservation of momentum and Gallilean relativity are inconsistent with each other.

What seems to have happened here is that you have performed a division by zero. When working out F = ma, otherwise I don't see where the infinity comes from.

In reality, when objects collide there is no instantaneous contact. The electron clouds around the constituent atoms repel each other which produces a smooth curve during a bounce. This curve is just so small and fast that it appears instantaneous from our perspective. So there is no division by zero in reality, it is just a flaw (though not immediately obvious) in your initial assumptions which makes the system unphysical.

Hope this helps.

Last edited: Dec 5, 2006
3. Dec 5, 2006

### D H

Staff Emeritus
Your local pool hall has all the equipment you need to test this theory.

4. Dec 5, 2006

### Danger

Well... pool balls are elastic, but as long as the shot force isn't extreme, the deformation is unnoticeable. The hard part is trying to keep them from rolling during the experiment, which gives a different result than if they were in space or on a frictionless surface. Should be good enough for an approximation, though.

Last edited: Dec 5, 2006
5. Dec 5, 2006

### MHefny

Danger...I agree with you...but the idea is that as long as there is deformation even unnoticable this means that the "virtuaL spring" will have a large K constant so an unnoticable deformation will the ball bounce back or move the other ball.

Jheriko...In your last paragraph you were so close to what I mean...yes the electrons make the roll of spring...

but my assumption is that "IF THERE IS A OBJECT THAT CANNOT BE DIVIDED"...
I am not sure bt I guess an example of this is when an eclectron collides with a positron they become energey as photoes comes out of the collision and they both disappear because there is no way to bounce as there is no deformation - I assume -
Thanks All for Help me...I still need more feedback from you regarding this issue.

6. Dec 5, 2006

### ZapperZ

Staff Emeritus
If that is true, then how do you explain that there can be electron-electron collisions that are elastic?

The electron-position anhilation really has nothing to do with an object disappearing because "there is no way to bounce" because both cannot be "divided". If that is true, then proton-antiproton anhilation wouldn't work, since each of them have constituents.

Zz.

7. Dec 5, 2006

### Jheriko

I assumed by unbreakable that you simply meant it had "infinitely" tough material properties. I didn't make the connection with that meaning "not made of atoms".

Even so, this model still violates conservation of momentum, its more reasonable imo to allow a singularity at the point of collision and have acceleration that is continuous almost everywhere and have conservation of momentum, than to have the object come to complete standstill.

I think my relativity point was a bit superfluous too... not quite sure what I was thinking about. The new 'law' remains consistent from either perspective. It does however show that even if both balls are moving no momentum transfer should take place since we can always choose an observer moving with the balls so as to make at least one of them appear static at all times.

8. Dec 5, 2006

### MHefny

ZapperZ... I assume the negative charge of electrons acts as the spring.

9. Dec 5, 2006

### ZapperZ

Staff Emeritus
Why can't you do the same with electron-positron? After all, all you need to do is simply change the SIGN of the force and voila, the mathematical expression is the same.

Remember what I objected to - that your assertion that all of this is due to the "structure", or lackthereof, of electrons. The criteria that you described to produce the effects are neither the necessary nor the sufficient criteria. The examples I gave negate that.

Zz.

10. Dec 5, 2006

### MHefny

First thank you all for this discussion it is really fruitful for me.

ZapperZ....I chose electron-positron because they are not the same charge. which means there would be no electric force that move them apart from each other and resist the collision.

Jheriko....Yes that is what I mean by unbreakable object...However if you allow a singularity at the point of collision with NO DEFORMATION at all and no fields such as electrical field acts as spring then how can the moving object moves the other one. Because this means that the still object moved from 0 to V in ZERO time "instantaniously" which is impossible because you need infinite energy to do that. Can we assume that it is more accepted to make the first object stops and all its Kinetic Energy gets out in sort of Photon ?

11. Dec 5, 2006

### ZapperZ

Staff Emeritus
This is highly confusing. You seem to think that only electron-positron collision would produce such a thing. What do you think is the first particle-particle collider ever built? It was the electron-electron collider built by Burton Richter! You might want to study the outcome of such a colllision, both what we have now, and what is possible within the Standard Model. You'll see that the switch in the "sign" of the charge really doesn't matter in terms of the complexity of what you could get out of the collision.

Zz.

12. Dec 5, 2006

### MHefny

Thank you ZapperZ I started to google for this topic...

In any collision there should be a spirng somewhere...can be the object as in regular balls, can be electric field or even weak or strong nuclear force acts as string in order not to violate the conservation of momentum...otherwise both objects will be still

What I assumed from the beginning is unbreabnle object that is not affected by any fields and can have no deformation at all.

Please let me know what do you think ?

Last edited: Dec 5, 2006
13. Dec 5, 2006

### ZapperZ

Staff Emeritus
I actually have no clue what you just said here, especially the

"....In any collision there should be a spirng somewhere...can be the object as in regular balls, can be electric field or even weak or strong nuclear force acts as string in order not to violate the conservation of momentum...otherwise.."

part.

Zz.

14. Dec 5, 2006

### Jheriko

ZapperZ, I think he means that all of these forces have effects which are spring-like, in the sense that they create a soft "bounce back" when two sources are launched at each other. I'm not sure if this is exactly true... but it might be since I know very little about the weak and strong forces.

There is nothing wrong with some particle carrying the excess energy away, I just think that it is nicer to conserve momentum without creating particles. The idea of some nasty thing happening with infinities isn't very nice, but i like the conservation of momentum enough to turn a blind eye, that and it allows us to find a solution for this situation which is nice almost everywhere and agrees with what my experience tells me.

In your case where the balls come to a complete standstill there is still some infinity involved, it is just less obvious perhaps. The ball goes from moving at a finite speed to zero in no time, this means that it has infinite acceleration during this infinitesimal amount of time. So the problem of this singularity is not removed by saying that the ball comes to a complete stop when it hits its counterpart and further we are left with a result which disagrees with intuition (at least my intuition anyway).

Last edited: Dec 5, 2006
15. Dec 5, 2006

### MHefny

So both solutions cannot resolve the issue of infinite acceleration either from V to Zero or vice versa.... So can we get the conclusion that it MUST be a deformation in shape, or in a field of force to make the Virtual String effect in order to make a collision as a collision without this string effect is not possible -according to the infinite acceleration that should take place in such a collision- ?

16. Dec 5, 2006

### ZapperZ

Staff Emeritus
I re-read, and re-read the OP, and this post. I am completely baffled as to what exactly you are trying to prove here. Other than the fallacy of defining what is a "solid" object for something like electrons, I am not exactly sure what you are attempting to do. Are you trying to break the conservation of momentum? And what is this "string" thing in here all of the sudden?

Zz.

17. Dec 5, 2006

### Staff: Mentor

Perhaps I can express ZZ's objection in a different way: Since your assumtion has nothing at all to do with reality, how is this discussion at all useful?

18. Dec 6, 2006

### MHefny

ZapperZ.. Please excuse my english..I mean spring effect not string effect.

russ waters.. I believe this has to do with reality because if we can inverse the problem we can say that the spring effect is essential for any collision.

Again thanks all for these fruitful discussion, it was of great benefit to me.

19. Dec 6, 2006

### ZapperZ

Staff Emeritus
Not sure how, since I certainly still don't understand what you are up to.

For example,what's with the "spring"? The potential for a "spring", which is a simple harmonic oscillator, has a form of U(r) = kr. On the other hand, the coulombic potential for a charge particle has the form of U(r)= k/r. They are not the same! So what "spring effect"?

You still haven't clearly described what you are trying to do.

Zz.