Understanding Momentum and Moment of Area Concepts | Explained by Experts

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Discussion Overview

The discussion revolves around the concepts of momentum, particularly the momentum of the center of mass of a system compared to the sum of the momenta of individual objects. Additionally, participants seek clarification on the first and second moments of area.

Discussion Character

  • Exploratory, Homework-related, Technical explanation

Main Points Raised

  • One participant questions why the momentum of the center of mass differs from the sum of the independent momenta of objects within a system.
  • Another participant expresses confusion stemming from a homework problem where they obtained different results for linear momentum when calculated separately versus using the center of mass approach.
  • A participant suggests that an error may have occurred in the calculations, indicating a need to review the details of the problem.
  • One participant describes their method of calculating momentum using the change in position of the center of mass, time interval, and total mass, but expresses uncertainty about the validity of this approach.
  • Another participant responds that the described method can be valid and requests further details to identify where the misunderstanding may lie.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the differences in momentum calculations, and multiple views on the correct approach remain. The discussion is unresolved regarding the specific errors in calculations and the understanding of the concepts involved.

Contextual Notes

Limitations include potential missing assumptions in the calculations and the need for clearer definitions of the first and second moments of area, which have not been fully explored in the discussion.

Red_CCF
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Hi

I was wondering if anyone could explain why the momentum of the center of mass of a system is different than the sum of the independent momentums of every object.

I also don't understand the concepts of the first and second moment of area. I would appreciate it if someone explained it to me.

Thanks for any help that you can provide
 
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Red_CCF said:
I was wondering if anyone could explain why the momentum of the center of mass of a system is different than the sum of the independent momentums of every object.
Why do you think it's different?
 
Doc Al said:
Why do you think it's different?

Because on a question for my homework, which asked for linear momentum of the system, I got two different answers when i did the momentum of each separately than doing the momentum of the center of mass.
 
Red_CCF said:
Because on a question for my homework, which asked for linear momentum of the system, I got two different answers when i did the momentum of each separately than doing the momentum of the center of mass.
I'd have to see the details, but I suspect you made an error.
 
Doc Al said:
I'd have to see the details, but I suspect you made an error.

If they are indeed the same then I probably did. I'll try to work out what I did wrong. Thanks.
 
Red_CCF said:
If they are indeed the same then I probably did. I'll try to work out what I did wrong. Thanks.

I think I figured out what I did but I don't really understand why. I did the change in position of the center of mass, divided it by the time interval, and multiplied the result by the total mass of the system and I got a very off answer. Can anyone explain why I can't do it this way? Thanks
 
Red_CCF said:
I think I figured out what I did but I don't really understand why. I did the change in position of the center of mass, divided it by the time interval, and multiplied the result by the total mass of the system and I got a very off answer. Can anyone explain why I can't do it this way? Thanks
You can do it that way. In order to find out where you went wrong, please describe the actual problem.
 

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