Predicting types of collisions

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    Collisions
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Discussion Overview

The discussion centers around the prediction of types of collisions, specifically focusing on elastic versus inelastic collisions as presented in a physics textbook. Participants explore the challenges of predicting collision types and the factors that determine the degree of inelasticity.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant questions whether predicting the type of collision requires advanced knowledge in material science or if there is a fundamental concept missing from the textbook.
  • Another participant seeks clarification on what is meant by "type of collision," specifically asking if it refers to elastic versus inelastic collisions.
  • A participant expresses the understanding that all real-life collisions are somewhat inelastic and that elastic collisions serve mainly as approximations.
  • There is a mention that predicting the degree of energy loss in collisions is complex, with the coefficient of restitution being a relevant measure that is typically determined through measurement rather than theoretical prediction.
  • A participant acknowledges the difficulty in finding information on the coefficient of restitution but finds it more intuitive after some reading.

Areas of Agreement / Disagreement

Participants generally agree that all realistic collisions involve some energy loss and that predicting the degree of inelasticity is challenging. However, there is no consensus on the fundamental principles required for predicting collision types.

Contextual Notes

The discussion highlights the complexity of predicting collision types and the reliance on empirical measurement for coefficients of restitution, indicating potential limitations in theoretical approaches.

crudux_cruo
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I've been working through Chapter 9 of Fundamentals of Physics (Center of Mass and Linear Momentum) and while I think I generally understand the different types of collisions, I notice that all of the problems state (or heavily imply) the type of collision after it has happened.

Does predicting the type of collision generally require knowing more advanced topics like material science, or am I missing something fundamental from the textbook?
 
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Welcome to PF.

What do you mean by "type of collision"? Elastic vs inelastic, or something else?
 
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Ibix said:
Welcome to PF.

What do you mean by "type of collision"? Elastic vs inelastic, or something else?

Thanks!

And yes, elastic vs inelastic. From what I understand all real life collisions are some degree of inelastic, with elastic collisions being useful mainly as an approximation.

Assuming I understand that correctly, I wanted to know what physically determined that 'degree of inelasticity'. I apologize if I am using improper or imprecise language here.
 
Yes, all realistic collisions involve some energy loss. I think you are correct that predicting the degree of energy loss from first principles is a hard problem. The number describing the degree of elasticity is the coefficient of restitution, which you can look up if you want. As far as I'm aware you usually just measure it for any given collision.
 
I appreciate the succinct response. I'm amazed I couldn't find it with a simple google search, but after doing some reading on COR the things are a fair bit more intuitive. I'm sure I'll confuse myself with it in a day or two though.
 
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Glad to help - sometimes it's just knowing the term to look for.
 
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