What makes a question too broad?

Question

I recently answered -How much forward force is exerted by an idling automatic car- but it was closed as too broad. I dont particularly care either way, and I respect the moderators judgment, but its closure confused me.

I understand it is a general question, broad because it does not specify the type of car, engine, transmission, etc. required to arrive at a precise value. But, in my opinion, lack of specificity does not invalidate the intent of the physical question asked. It is possible to demonstrate the physics involved; applying reasonable assumptions, a useful answer is possible. Even fully specified, an exact answer is not possible (without extensive experimental data) or required to provide a useful answer.

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There are many broad, useful questions without exact answers.

For example - Is it (practically) possible for a large building to be a Faraday cage?: Dimensions, materials, and signal strengths are not specified (needed to determine the effective strength). The physical concept is discussed in relative terms, yet this is undoubtedly a useful answer.

Physical concepts and practical assumptions often provide useful answers to questions that lack specificity. Unless explicitly stated, we assume collisions act on the centers of mass, etc. Concepts and approximations are often more useful than mathematical proofs. How are these factors considered?

When are questions considered broad enough to be closed?

Answer 1

I tend to use the too broad close vote for one of three reasons:

1. the answer would need to cover a lot of ground & be rather lengthy (e.g., "a book chapter" long)
2. there is too little information in the post to give a meaningful answer
3. the post is looking for a list

In this case, I thought there to be not enough information (the answer depends on car type, car size, engine size & power, road conditions, and so on down the line) and voted accordingly.

I note here, probably simply as an aside, that answers do not make a question on topic. So when we vote, we're looking at the content of the question itself and judging on that alone.

But, in my opinion, lack of specificity does not invalidate the intent of the physical question asked

Ultimately, I think your statement here could be used as the basis for eliminating the too broad close reason altogether. Think about it: if someone can fill in values for missing parameters with "whatever sounds reasonable," then why bother saying that someone needs to narrow their question down? Someone could just "fill in the blanks."

And so I reject this notion entirely. A requirement of a minimum level of specificity is absolutely needed to ensure a quality answer to a quality question (though I imagine that minimum level is probably subjective, but that's why we require 5 reviewers). I don't think that was the case for this particular question (though it could probably be improved & reopened), and it seems that I was agreeing with 4 other people & disagreeing with 1 person.