Collision of a billiard ball against a wall

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Discussion Overview

The discussion revolves around the nature of the collision between a billiard ball and a wall, specifically whether it can be considered elastic. Participants explore the definitions and characteristics of elastic collisions, the energy transfer involved, and the implications of sound and heat in such interactions.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants propose that the collision is considered elastic because the wall does not absorb a significant amount of energy from the ball.
  • Others argue that while the wall feels the momentum of the ball, it remains stationary due to its firmness, and most energy is converted into sound rather than heat.
  • There is a suggestion that the definition of an elastic collision hinges on the low energy dissipation by the wall.
  • One participant emphasizes that an elastic collision is defined as one where the total kinetic energy before and after the encounter remains equal.
  • Another participant notes that in an ideal elastic collision, no energy is converted into sound, but acknowledges that in practical scenarios, some energy does go into sound.
  • It is mentioned that the original poster's question implies a misunderstanding of perfect elasticity, as the collision is not perfectly elastic due to energy loss to sound.

Areas of Agreement / Disagreement

Participants express differing views on the nature of energy transfer during the collision, with some agreeing on the definition of elastic collisions while others challenge the applicability of that definition to the scenario discussed. The discussion remains unresolved regarding the extent to which the collision can be considered elastic.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about energy transfer and the definitions of elastic versus inelastic collisions. The participants do not reach a consensus on the nature of the collision in practical terms.

themagiciant95
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The collision of a billiard ball against a wall is considered elastic. Intuitively i can accept it. But analytically i don't understand it.

Why does the wall not take any relevant amount of energy from the ball? Is it connected to the change in temperature of the wall ?
What scenarios can we approximate as elastic ? Under what characteristics ?
 
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The wall definitely feels the momentum of the ball. The wall is just very firm. It isn't going to move. Most of the energy just gets transferred into sound, not as much in heat.
 
lekh2003 said:
The wall definitely feels the momentum of the ball. The wall is just very firm. It isn't going to move. Most of the energy just gets transferred into sound, not as much in heat.

So the only fact that allows us to consider the collision as elastic, is that the energy dissipated by the wall is very low ?
 
themagiciant95 said:
So the only fact that allows us to consider the collision as elastic, is that the energy dissipated by the wall is very low ?
That is the definition of elastic collision.
 
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themagiciant95 said:
So the only fact that allows us to consider the collision as elastic, is that the energy dissipated by the wall is very low ?
A.T. is correct, an elastic collision is defined as a collision where the energy is transferred to other methods of energy transfer besides collisions.
 
lekh2003 said:
A.T. is correct, an elastic collision is defined as a collision where the energy is transferred to other methods of energy transfer besides collisions.
Nice that we agree, but I don't understand your definition at all. Why not keep it simple:

https://en.wikipedia.org/wiki/Elastic_collision

"An elastic collision is an encounter between two bodies in which the total kinetic energy of the two bodies after the encounter is equal to their total kinetic energy before the encounter."
 
A.T. said:
Nice that we agree, but I don't understand your definition at all. Why not keep it simple:

https://en.wikipedia.org/wiki/Elastic_collision

"An elastic collision is an encounter between two bodies in which the total kinetic energy of the two bodies after the encounter is equal to their total kinetic energy before the encounter."
Sure, I might be going on a tangent. But yes, the total energy is conserved, even if that requires energy going into sound.
 
lekh2003 said:
Sure, I might be going on a tangent. But yes, the total energy is conserved, even if that requires energy going into sound.
In an ideal elastic collision the total macroscopic kinetic energy is conserved. No energy goes into sound.
 
A.T. said:
In an ideal elastic collision the total macroscopic kinetic energy is conserved. No energy goes into sound.
But in the OP's question, it is not perfectly elastic, some of the energy goes into sound. I find that it would be better not to discuss perfectly elastic collisions since the OP is familiar with this.

The OP is questioning how the collision can be perfectly elastic which it is not.
 

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