About elastic and inelastic collision

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Discussion Overview

The discussion revolves around the definitions and conditions of elastic and inelastic collisions, particularly focusing on the criteria for classifying a collision as inelastic. Participants explore the relationship between the sticking of objects and the conservation of kinetic energy.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant cites a text definition stating that inelastic collisions occur when two objects stick together after a collision, questioning its sufficiency.
  • Another participant argues that the instructor's clarification suggests that sticking together is not a necessary condition for inelastic collisions, emphasizing the importance of kinetic energy conservation.
  • It is noted that if objects do not stick together, the collision could still be classified as either elastic or inelastic based on whether kinetic energy is conserved.
  • Some participants introduce terms like "completely inelastic" for collisions where objects stick together, and "partially elastic" or "partially inelastic" for cases where they do not stick but kinetic energy is not conserved.

Areas of Agreement / Disagreement

Participants express differing views on the definitions and conditions of inelastic collisions, indicating that multiple competing interpretations remain unresolved.

Contextual Notes

There is ambiguity regarding the definitions of necessary and sufficient conditions in the context of collision types, as well as the terminology used to describe different scenarios of energy conservation.

KFC
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I am studying the collision from the text, in which they said inelastic collision is the case when two collide objects stick together after collision. But in the class, the instructor said two objects stuck together is not the sufficient condition for inelastic collision, we should figure out if the kinetic energy conserved or not. So which one is right and why?
 
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KFC said:
I am studying the collision from the text, in which they said inelastic collision is the case when two collide objects stick together after collision. But in the class, the instructor said two objects stuck together is not the sufficient condition for inelastic collision, we should figure out if the kinetic energy conserved or not. So which one is right and why?

Neither, if you've quoted your instructor correctly (but I'd bet a fair amount that he didn't say "sufficient", he said "necessary", in which case he's right).

An elastic collision conserves kinetic energy; an inelastic collision does not.

If the colliding objects stick together, that's a sufficient but not a necessary condition for the collision to be inelastic.
 
In other words, if the objects don't stick together, the collision may be either elastic or inelastic, depending on whether KE is conserved or not.

We sometimes call the case where the objects stick together "completely inelastic", and the cases where they don't stick together but KE is not conserved "partially elastic" or "partially inelastic".
 
Thanks guys for your explanation.
 

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