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Stack Exchange explicitly encourages writing a self-answer, when appropriate.


Derek Muller posted a video about a wind-powered vehicle that can go downwind faster than that downwind itself.

(The design of the vehicle dates back multiple years, but building one that is large enough to move a human (and not kill the human by falling apart) has proved challenging, by the looks of it.)

In the video Derek himself indicated that he was not quite confident that he understood the physics of it. I anticipated that questions would start coming in on physics SE, so I posted a self-answer.

Now, this being a self-answer it felt silly to pretend (in the question) that I didn't know the answer.

Also the subject is:
'A wind-powered vehicle on wheels that can go downwind faster than the wind itself.' I assumed that any physicist would immediately go: "Hang on, how is that possible?"

The question was closed on the grounds: 'needs details or clarity'.

So I'm asking for opinion here.
It seems petty to me to close a question because the obvious isn't stated explicitly.

For the future:
Should the question part of a self-answer be phrased as if you don't know the answer?

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I was one of the close voters, but I voted to close as engineering not as unclear.

If you just read the question then I think it is unclear, so I can see why people have voted that way. When I post a self answered question I usually make the question as brief and clear as possible. If I were writing it I would have just written "How can this vehicle described in the Veritasium video travel faster than the wind?" - well, I would elaborate a bit but I'd still keep the question brief and simple. Then I would wax lyrical in the answer.

Having reread it I think voting to close as an engineering question is unkind so I've voted to reopen. However I think self answered questions work best when they address an important and fundamental principle in physics and I'm not sure that applies here.

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    $\begingroup$ Yeah, in retrospect: when preparing a self-answer: I should think of the question as setting the stage. In the question: the minimum to make the subject explicit; all other information in the answer. Also: in a future self-answer I will announce explicitly that the question is for the purpose of presenting a self-answer. $\endgroup$
    – Cleonis
    May 30 at 8:53
  • $\begingroup$ Since the Veritasium video already answers the question with an animation showing how the propeller is equivalent to two sailboats operating in a configuration where (as every sailor has known for millennia) they can sail faster than the wind speed, arguably there is no question to answer. $\endgroup$
    – alephzero
    Jun 2 at 11:41
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    $\begingroup$ @alephzero Using that logic no one should ask questions on PSE if the answers can be found elsewhere. $\endgroup$ Jun 2 at 13:01
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Due to the nature of Stack Exchange as a Q&A site, there should at least be an explicit question to be answered. The most common trap of posting a question for self-answering is that the question usually lacks enough detail for other readers and potential answerers.

Regardless of self-answer or not, all questions are expected to be self-contained: has enough context/background, not too depending on external sources to understand the issue, has an explicit question to be answered, etc.

The quality of the questions should be judged independently regardless of the existence of the answers, and they should also be answerable by others, not only the asker.

Just a commentary on this specific question:

  • The first revision was not self-contained at all. No one could possibly understand the topic without watching the video, and there's also no question.
  • The second revision was far better; there was the context (and additional speculation possibly as a research effort), but still, no question.
  • The third revision is now okay with the explicit question to be answered. (Usually, there's no need to mention meta-commentary about self-answer as the purpose, but it's still okay)
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When I post a self-answer, is it expected that in the question I should pretend I don't know the answer?

In a word, yes. Stack Exchange is an open Q&A site, and self-answered Q&As should be open to the possibility that someone else can come along and provide an even better answer to the question than the one you initially wrote. (If you're not prepared for that possibility, and you're not prepared to answer any such alternative answers, then a self-answered Q&A is not the venue you're looking for $-$ you're looking for a blog instead.)

In addition, having a clear question in the Question part of the thread is particularly useful in clarifying the scope of the material that the Answer section will explore. This helps potential readers decide quickly and effectively whether the thread they have landed on will be interesting and useful for their purposes.

If you want good (and bad) examples of how this can work, see this SEDE query, which contains all of the self-answered Q&As (i.e. questions with immediate self-answers) sorted by score.


As far as your specific link is concerned, I have not interacted with it much, but one thing that sticks out immediately is the title:

The nice Veritasium video about a wind-powered vehicle that can go downwind faster than the wind itself

There is no question there, and that's an immediate red flag. The Question, starting with the title, should make it very clear what question is being posed in that thread. If it doesn't, then it should be closed as lacking clarity.

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