How can a true elasic collision exist?

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Discussion Overview

The discussion revolves around the concept of elastic collisions, particularly questioning the existence of true elastic collisions in both microscopic and macroscopic contexts. Participants explore theoretical implications, practical examples, and the conditions under which collisions can be considered elastic or inelastic.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant expresses confusion about the concept of elastic collisions, suggesting an analogy of atoms colliding like wine glasses, and questions the absence of energy loss.
  • Some participants argue that true elastic collisions cannot exist in macroscopic objects, although they acknowledge that steel balls at normal lab speeds can approximate elastic behavior.
  • Another participant emphasizes that while microscopic particles can collide elastically, the introduction of energy thresholds (like excitation or ionization) can lead to inelastic collisions.
  • It is noted that in macroscopic collisions, thermodynamic properties cause energy loss in the form of heat and increased disorder, making true elasticity unattainable.
  • A participant mentions that elastic collisions in nuclear physics are well understood, highlighting the conservation of momentum and energy without additional factors like the coefficient of restitution.

Areas of Agreement / Disagreement

Participants generally disagree on the existence of true elastic collisions, with some asserting that they are impossible in macroscopic contexts while others maintain that they can occur at the microscopic level. The discussion remains unresolved regarding the implications of these differing views.

Contextual Notes

There are limitations in the definitions of elasticity and the conditions under which collisions are considered elastic or inelastic. The discussion reflects varying interpretations based on scale (microscopic vs. macroscopic) and the influence of thermodynamic properties.

Daveman20
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Is this something I just have to accept? How can there be no loss of energy/heat when I've always been taught otherwise. I imagine an elastic collision to be like the electromagnetic force field around an atom that just chimes when it hits another spherical force field around a different atom, like two wine glasses bumping together. Is this a good way to imagine it? Thanks in advance
 
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There can't (although something like steel balls at normal lab speeds are pretty close)
It's just one of those things like massless springs and friction free slopes that make it possible to see the main points
 
mgb_phys said:
There can't (although something like steel balls at normal lab speeds are pretty close)
It's just one of those things like massless springs and friction free slopes that make it possible to see the main points

Thank you, mgb, my intuition remains undefeated! Wikipedia almost had me convinced otherwise.
 
Daveman20 said:
I imagine an elastic collision to be like the electromagnetic force field around an atom that just chimes when it hits another spherical force field around a different atom, like two wine glasses bumping together.
If you can hear the collision, it is inelastic.

Bob S
 
Microscopic particles like gas atoms collide elastically.If the energy of collision becomes equal to or greater than an excitation or ionisation energy the collisions can become inelastic.
 
Microscopic particles (like atoms or electrons) can easily collide elastically. This is a well known type of collision in nuclear physics. This is just a reflection that the particles must obey conservation of momentum and energy directly, with no "coefficient of restitution" or anything like that.

If you're talking about macroscopic objects like balls, then elasticity is a thermodynamic property. In other words, any time you cause deformation in a macroscopic material, you have some kind of thermodynamic material property which causes a correlated production of heat and increases disorder among the molecules in the material. These byproducts like heat take away energy from the momentum. So, along these lines, you never have true elasticity in macroscopic objects.
 
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