Momentum Conservation Between Two Masses

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Discussion Overview

The discussion revolves around the conservation of momentum during collisions between two objects of equal mass, particularly focusing on elastic and inelastic collisions. Participants explore why, in certain scenarios, one object may stop while the other moves away with all the momentum, and how kinetic energy conservation plays a role in these interactions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions why, in a collision between two equal masses, the first object stops completely while the second takes on all the momentum, rather than both sharing the momentum equally.
  • Another participant notes that for momentum to be conserved, the scenario described must also conserve kinetic energy, which leads to a unique solution where the first object stops and the second moves away with all the momentum.
  • A third participant reiterates the importance of kinetic energy conservation in elastic collisions and emphasizes that total momentum is always conserved, regardless of the type of collision.
  • A fourth participant introduces the concept of completely inelastic collisions, where two objects of equal mass move together after the collision, suggesting that momentum distribution can differ based on the type of collision.

Areas of Agreement / Disagreement

Participants express differing views on how momentum is distributed in elastic versus inelastic collisions, indicating that multiple competing perspectives exist regarding the mechanics of these interactions. The discussion remains unresolved as participants explore these different models.

Contextual Notes

There are limitations in the assumptions made regarding the types of collisions and the conditions under which momentum and kinetic energy are conserved. The discussion does not resolve the complexities involved in these scenarios.

Greatness
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I have been studying momentum and began believing that I understood it, but I began thinking...

Between two objects of the same mass, the first object will collide with another object (let's say the second object is not moving) and the momentum, in an isolated system, will be transferred, stopping the first object. However, why is this? Why is half of the momentum not transferred to object 1 and another to object 2?
 
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You are right that momentum would be conserved if half the momentum ended up with each object (after the collision, they're both moving at speed v/2). But we also have to conserve energy, and in the elastic collision that you are describing no kinetic energy is lost to heat or crushing and deforming the colliding masses, so the kinetic energy after the collision has to be equal to the kinetic energy before.

Kinetic energy is given by ##E=\frac{mv^2}{2}##, and there's only one solution that conserves this quantity as well as the momentum ##p=mv## and that's the one in which the first object stops dead and the second ends up with all the momentum.
 
Greatness said:
I have been studying momentum and began believing that I understood it, but I began thinking...

Between two objects of the same mass, the first object will collide with another object (let's say the second object is not moving) and the momentum, in an isolated system, will be transferred, stopping the first object. However, why is this? Why is half of the momentum not transferred to object 1 and another to object 2?

In this situation, as has already been pointed out, the KE has to stay the same (elastic collision). But keep in mind that the total momentum of the system is always conserved, in elastic and inelastic collisions.
 
Greatness said:
Between two objects of the same mass, the first object will collide with another object (let's say the second object is not moving) and the momentum, in an isolated system, will be transferred, stopping the first object. However, why is this? Why is half of the momentum not transferred to object 1 and another to object 2?

In a plastic (or completely inelastic) collision of two ball of equal mass this is how the momentum is distributed. They each have half of the original momentum. And they move together.
Conservation of momentum alone is not sufficient to determine the redistribution of momentum after collision.
 

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