What would be the result of this collision?

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Discussion Overview

The discussion revolves around the outcome of a completely inelastic collision between two particles moving towards each other in a one-dimensional closed system. Participants explore the implications of conservation laws, particularly momentum and energy, in the context of inelastic collisions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that both particles will come to a stop after the collision, while another proposes they will reverse direction with unchanged velocity.
  • Another participant emphasizes that in a completely inelastic collision, momentum is conserved, and invites the original poster to express the conservation of momentum mathematically.
  • There is a discussion about energy conservation in a closed system, with one participant asserting that energy is conserved but can transform into other forms, such as phonons.
  • Some participants clarify that in a completely inelastic collision, the particles stick together, leading to a scenario where they stop moving due to momentum conservation.
  • One participant raises the need to define what is meant by "inelastic," suggesting that energy may not be lost but transformed into other forms within the system.

Areas of Agreement / Disagreement

Participants generally agree on the conservation of momentum in inelastic collisions, but there is disagreement regarding the specifics of energy conservation and the definitions of inelastic collisions. The discussion remains unresolved on the exact outcomes of the collision.

Contextual Notes

There are limitations regarding the assumptions made about energy transformations and the definitions of inelastic collisions, which are not fully clarified in the discussion.

cshum00
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-Let's say that in this system particles are only allowed to move in one dimension.
-There are 2 particles moving towards each other.
-Both particles have same mass and velocity.

What will be the result of the inelastic collision?
a) Both particles will come to a stop and no longer move.
b) They will move to the opposite of their original direction with no change in velocity.

I haven't done the math yet but my intuition tells me from the waves behave is that both velocity vectors would cancel each other. But from my knowledge of inelastic condition tells me that their velocity vectors will exchange.
 
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(I am assuming you mean a completely inelastic collision??)

Even though the kinetic energy is not conserved in an inelastic collision, there is still conservation of momentum. Can you write out the conservation of momentum?
 
Yes, complete inelastic collision.
And let's add that it is a closed system.
So in a closed system, isn't energy supposed to be conserved?
 
cshum00 said:
Yes, complete inelastic collision.
And let's add that it is a closed system.
So in a closed system, isn't energy supposed to be conserved?

If it is a completely inelastic collision then the masses would stick together. So the resultant would be that they both stop using conservation of momentum.
 
cshum00 said:
Yes, complete inelastic collision.
And let's add that it is a closed system.
So in a closed system, isn't energy supposed to be conserved?

If you start calling the "inelastic collision" in a closed system, then you need to define inelastic. Usually it means that any energy transferred to it will sink out into phonons, or some potential somewhere. So really it stays in the system, its just no longer the kinetic energy of the particle. In elastic it would be such that the energy does NOT go into some other form but rather stays as the particles kinetic, and is just transferred.
 
cshum00 said:
So in a closed system, isn't energy supposed to be conserved?
Absolutely. The conservation of energy is "always" true, otherwise you are putting a lot of us that studied physics back to square one. Fact is that the energy can change from one form to the other. Therefore, in your system, the kinetic energy is not conserved, but has been transofrmed into another for of energy, which phonon production is very likely, this is not the only possible way.

Cheers
 

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