Why was my comment deleted?

I had a comment on this answer to my question which both clarified that one of my definitions was correct (F = m * a is correct, but not super helpful in this situation), and then also provided external sources where people could learn more information to help them understand the answer. (Especially since I did not understand the answer until I used those resources.)

Why would such a comment be deleted? My hunch is that external sources are discouraged, but the usual rationale for that I've heard is that they could be removed later, so you include the relevant information from the sources and then link to them so people can verify it for themselves. In this case, the useful information was already in the answer itself, so I was providing extra resources for people who wanted clarification. As far as I was aware, linking to external sources is helpful as long as those sources exist, and when they don't, then that comment should be deleted. (And even then, it's often helpful to still have the comment because the Internet Archive will often still have archived versions of the linked site.)

Why was my comment deleted? What was the rationale, and what should I have done better? (And, if it's applicable, is the rationale something that should be applied to other SE sites as well? I'm fairly new to physics stack exchange.)

First, thanks for coming to meta and asking!

It's not your hunch, though. We don't discourage using external sources; actually, it's encouraged to link or cite useful and relevant external resources whenever appropriate, but when doing so in a question or answer, you need to do it in such a way that your question or answer makes sense even to a reader who won't or can't access the source. (This isn't so important in comments.)

What happened with your comment is this: comments are meant for suggesting improvements to the post they're attached to. This includes things like

• Requesting clarification on an unclear aspect of the post, which implicitly suggests that the post's author clarify that aspect
• Pointing out an error in the post, which implicitly suggests that the author fix the error
• Linking to a related resource and suggesting that the author edit their post to include the link

and so on. Your comment didn't seem to be doing any of these things. It looked like it was making a statement which didn't have anything to do with the answer, and that's why I deleted it.

Here is the text of the deleted comment (with dummy URLs):

To be clear, Newton's second law F = m * a is correct, but thinking of force as a change in momentum over time is useful. Here is a source with the correct definition of work, and another source with an explanation as to how you get from F = m * a to F = p / t (where p is momentum).

Now that you've made this meta post, if I understand correctly, it sounds like you had two goals with this comment:

• Suggest that the answer's author was wrong in saying "Your definitions are incorrect" (because you quoted one definition, $$F = ma$$, which was correct), and ask that they fix that
• Suggest that the answer's author add links to the two webpages you linked into their answer

I think a better way to make these suggestions is to phrase them as questions. For example, respectively:

• Something like "Actually I did include one correct definition ($$F = ma$$), so I don't think it's fair to say that my definitions are incorrect" would work for the first goal.
• And something like "Could you add a link to this website which gives the definition of work? And I don't think it's clear how to get from $$F = ma$$ to $$F = p / t$$. Would you consider adding a link to this website which explains it?" for the second goal.

I would point out, though, that a lot of people might consider it a bit arrogant, as the person who asked the question, to act like you have better references than the poster of the answer could find on their own. So a better phrasing would be just asking for clarification, like "I don't understand how to get from $$F = ma$$ to $$F = p/t$$. Could you clarify that?"

Once you do this, it's up to the author of the answer to decide whether to accept your suggestions or not. If the author decides not to accept your suggestions, then if you think they're important enough, you can post a separate answer that incorporates your suggestions. Otherwise, I'd suggest just letting it go.