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https://physics.stackexchange.com/questions/89374/velocity-at-the-very-moment-of-collision

Some comments are posted on this question out of which I flagged these two:

1 The last part is a duplicate of: physics.stackexchange.com/questions/35177/… – jinawee

2 An addendum to @ja72's comment is that all composite objects must in reality d the store and release business . – dmckee♦.

I flagged the comment no 1 two times, first because I had edited my question and explained that the last part of my question was duplicate of this question not that "jinawee" mentioned but my flag was declined.

then I again edited my question and removed the duplicate part, after editing I again flagged comment no 1 as obsolete but it was again declined.

I flagged comment no 2 as not constructive because I don't find it related to the question one time and it was declined. And after this, the comment was rephrased with minor improvement of d replaced with do. As

An addendum to @ja72's comment is that all composite objects must in reality do the store and release business. – dmckee♦


Why were my flags to these comments declined?

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    $\begingroup$ I don't quite understand your first flag. What were you trying to achieve? Unless your question was in danger of closure as a duplicate, you don't have to defend yourself. If you don't like quite so much that the incorrect reference is in the comments, leave a comment yourself and post the correct link. There's not a lot that moderators can't do there - and they certainly shouldn't delete a comment just because you disagree with it on technical grounds. $\endgroup$ – Emilio Pisanty Dec 11 '13 at 18:26
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    $\begingroup$ I left off acting on those as I am involved. Aside form the edit using my moderator superpowers. $\endgroup$ – dmckee Dec 11 '13 at 18:58
  • $\begingroup$ @EmilioPisanty before i raised my 1st flag i myself left a comment saying "Now this is question is similar to..." because in my question also i replaced "collision of photon" with "collision as occurs in compton scattering" but after my 1st flag was declined i completely removed the case of photon from my question and thats why i deleted my own comment. i don't see how my question is and was related to the link mentioned by jinawee. since i had left my own comment before raising the 1st flag the comment of jinawee became obsolete because i addresed to what my question was duplicate of. $\endgroup$ – user31782 Dec 12 '13 at 4:09
  • $\begingroup$ about my 2nd flag as i removed the duplicate portion of my question the comment of jinawee became obsolete. moreover my question in a genral way is not related to the thomson or reyleigh scattering. $\endgroup$ – user31782 Dec 12 '13 at 4:12
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I'm not a moderator, but FWIW I found jinawee's comment useful as it linked to an article that was related if not an exact duplicate. I would not want the comment deleted.

dmckee's comment expands on ja72's to point out that special relativity demands any composite object cannot be rigid. This also seems to me to be a useful point and again my view is that the comment should stand.

As Emilio says above, you can add a comment yourself to point out problems with someone else's comment, but those comments would normally not be deleted unless they are offensive or gratuitously pointless.

Response to comment:

In your question, during the collision the ball has no single well defined velocity because it is an elastic object and as it deforms different parts of the ball are moving at different speeds. So it isn't clear what is meant by the velocity at the moment of the collision.

You might ask could we have a perfectly rigid ball, but special relativity sets an upper limit on the rigidity of macroscopic objects because pressure waves in the object cannot move faster than light. Therefore no perfectly rigid objects can exist.

dmckee was pointing out that all real balls must deform and store energy as they hit the wall, then go back to their original shape and release energy as they bounce off the wall. Hence the impact takes a finite time and we have the problem of an ill defined velocity during the collision. In his comment the word business just means activity or what happens rather than some commercial enterprise. I'm afraid it's another example of English being a confusing language.

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    $\begingroup$ @anupam: I've edited my answer to respond to your comment. $\endgroup$ – John Rennie Dec 12 '13 at 7:24
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    $\begingroup$ @anupam Please accept my apologies for my confusing language. As John says "business" is meant in a very general way like sense 2 on the Merriam-Webster definition for the word. Or perhaps sense 4. $\endgroup$ – dmckee Dec 13 '13 at 2:59

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