Elastic vs inelastic collisions formulas

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Discussion Overview

The discussion revolves around the differences between elastic and inelastic collisions, focusing on the relevant formulas and principles that govern these types of collisions. Participants explore the conservation of momentum and kinetic energy, as well as specific scenarios and examples related to both collision types.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant expresses confusion regarding the formulas associated with elastic and inelastic collisions and seeks additional examples or tricks for solving related problems.
  • Another participant suggests using momentum conservation for all collisions and notes that energy conservation applies specifically to elastic collisions, while perfectly inelastic collisions result in objects sticking together.
  • A participant outlines that kinetic energy (KE) is conserved in elastic collisions, whereas it is not conserved in inelastic collisions, emphasizing that momentum is conserved in both types.
  • There is a clarification regarding the terminology of "elastic," where one participant explains that in physics, it refers to hard collisions (like steel ball bearings) rather than soft, stretchy objects, which may lead to confusion.
  • Another participant mentions that in elastic collisions with equal masses, the velocities of the objects are interchanged, while a specific formula can be used when masses are not equal.

Areas of Agreement / Disagreement

Participants generally agree on the fundamental principles of conservation of momentum and kinetic energy in elastic and inelastic collisions. However, there are nuances in understanding the terminology and specific scenarios that remain contested or unclear.

Contextual Notes

Some assumptions about the conditions of the collisions, such as the nature of the objects involved and the context of the collisions (e.g., perfectly elastic vs. perfectly inelastic), are not fully explored. The discussion also does not resolve the potential confusion surrounding the terminology used in describing elastic collisions.

oneplusone
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When doing practice problems from my textbook, I often get confused with both of them.
MOre specifically there are usually formulas which pertain to only one of those types of collisions.

Ex: [itex](v_1-v_2)_i = -(v_1-v_2)_f[/itex]

Does anyone know more of these types of formulas, or tricks to solve these equations?

Thanks.
 
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oneplusone said:
Does anyone know more of these types of formulas
Sure, your textbook.

or tricks to solve these equations?
- you can always use momentum conservation
- in elastic collisions, you can use energy conservation in addition
- in perfectly inelastic collisions, the objects stick together afterwards, so they have the same velocity
- in the center of mass system, all those collisions are easy to study

All equations are just a result of those ideas.
 
Elastic collisions: KE is conserved, momentum is conserved
Inelastic collisions: KE is not conserved, momentum is conserved.
This is a reasonable starting point
 
Also, don't be confused by the word "elastic." In common usage, "elastic" is like a rubber band or a balloon, that is, something "stretchy." BUT, when we say "elastic collision" in physics, examples are hard steel ball bearings (like you see in a Newton's Cradle toy) or billiard balls. Collisions of soft stretchy things (like soft rubber balls) are likely to be "inelastic." Confusing? I thought so when I learned this stuff the first time.
 
elastic collision

if masses of two objects is same than in elastic collision there velocities get interchanged and if masses are not equal than you can use the formula which u have given for elastic collision.
 

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