Quantcast
  • Register
PhysicsOverflow is a next-generation academic platform for physicists and astronomers, including a community peer review system and a postgraduate-level discussion forum analogous to MathOverflow.

Welcome to PhysicsOverflow! PhysicsOverflow is an open platform for community peer review and graduate-level Physics discussion.

Please help promote PhysicsOverflow ads elsewhere if you like it.

News

PO is now at the Physics Department of Bielefeld University!

New printer friendly PO pages!

Migration to Bielefeld University was successful!

Please vote for this year's PhysicsOverflow ads!

Please do help out in categorising submissions. Submit a paper to PhysicsOverflow!

... see more

Tools for paper authors

Submit paper
Claim Paper Authorship

Tools for SE users

Search User
Reclaim SE Account
Request Account Merger
Nativise imported posts
Claim post (deleted users)
Import SE post

Users whose questions have been imported from Physics Stack Exchange, Theoretical Physics Stack Exchange, or any other Stack Exchange site are kindly requested to reclaim their account and not to register as a new user.

Public \(\beta\) tools

Report a bug with a feature
Request a new functionality
404 page design
Send feedback

Attributions

(propose a free ad)

Site Statistics

205 submissions , 163 unreviewed
5,082 questions , 2,232 unanswered
5,353 answers , 22,789 comments
1,470 users with positive rep
820 active unimported users
More ...

  In the angular momentum equation L = r x p, which one of the remaining variables’ magnitudes is correctly conserved when the magnitude of the radius changes?

+ 0 like - 1 dislike
2242 views

For the equation L = r x p, assuming that the implied rotation occurs around a central point.

Premise 1: 

There is a force at all times directed from the point mass along the radius toward the centre of rotation (centripetal force).

Premise 2: 

A change in the magnitude of radius is conducted by altering the magnitude of this force.

Premise 3:

There can be no component of this force perpendicular to the radius. 

Premise 4: 

In order to affect the magnitude of the component of momentum perpendicular to the radius, one must apply a parallel component of force (Newton’s first law).

Deduction: 

A change in the magnitude of the radius cannot affect the magnitude of the component of momentum perpendicular to the radius.

Conclusion:

In the equation L = r x p, assuming that the implied rotation occurs around a central point, it is the magnitude of the component of momentum perpendicular to the radius that must be conserved when the magnitude of the radius changes. 

Closed as per community consensus as the post is neither graduate-level, nor coherent nor a question
asked Aug 28, 2017 in Closed Questions by Mandlbaur (-50 points) [ no revision ]
recategorized Aug 29, 2017 by Dilaton

This is not graduate-level, voting to close.

Are you proposing that an absolute proof that the laws of physics are flawed and require a change is something that should be dealt with at a level below graduate?

1 Answer

+ 1 like - 1 dislike

You must employ the equations of motion $\dot{{\bf{p}}}=\bf{F}$ in order to derive your conclusions. If there is no force perpendicular to the radius, then the corresponding part of momentum is conserved.

answered Aug 29, 2017 by Vladimir Kalitvianski (102 points) [ no revision ]

Such high-school level questions should not be answered on PO

@Dilaton: Instead of downvoting my answers, I propose you to develop means for deleting such questions. No votes are necessary for that.

So you agree with my conclusion then "the corresponding part of momentum is conserved" `so why do you word your reply as if you do not agree? 





user contributions licensed under cc by-sa 3.0 with attribution required

Your rights
...