# What are good examples of narrowing a homework question down to a conceptual question?

It is obvious that Physics SE community aren't here to solve specific physics problems. Homework policy, however, states that a question can be narrowed down to a conceptual question. To reinforce what has been said,

As a general rule, we do not discourage homework questions, as long as they are related to physics. But do keep in mind that Physics Stack Exchange is not primarily a homework help site; it's a place to get specific conceptual physics questions answered.

Then, we can conclude that we're free to ask a conceptual question concerning where we're stuck while solving a specific physics problem. For instance,

X: A man walks 7 km in 2 hours and 2 km in 1 hour in the same direction. What is the man's average speed for the whole journey? For this problem, I need a conceptual approach.

Y: You can use $$S = \dfrac{\Delta x}{t}$$ to compute average velocity.

Can this be a good example of a conceptual question? The steps are given in a conceptual approach without computing any specific values. I hope this is welcome.

A man walks 7 km in 2 hours and 2 km in 1 hour in the same direction. What is the man's average speed for the whole journey? For this problem, I need a conceptual approach.

This absolutely would not be an acceptable question on this site.

The statement "I need a conceptual approach" is pretty meaningless, or at least plays no role in helping us understand what exactly you are stuck on. And without that, all that's left is a pure homework problem without even the slightest indication of any effort or understanding on your part. Most such questions get closed and quickly downvoted, often to a score of -4 to -6, because it looks like you're trying to cheat on your homework, but also because we consider it fairly rude to ask for our help without putting in any work of your own.

I think the closest you could get to making this question acceptable for this site would be something like this:

Here is a problem I've been trying to do:

A man walks 7 km in 2 hours and 2 km in 1 hour in the same direction. What is the man's average speed for the whole journey?

I made a list of the information I have available:

• first distance: $$7\ \mathrm{km}$$
• first time: $$2\ \text{hours}$$
• second distance: $$2\ \mathrm{km}$$
• second time: $$1\ \text{hour}$$

I tried putting the distances and times together to get the totals, $$9\ \mathrm{km}$$ and $$3\ \text{hours}$$, and I also tried calculating the speed in each part, getting $$3.5\ \mathrm{km/h}$$ for the first part and $$2\ \mathrm{km/h}$$ for the second part. I know I need to find average speed, but I don't know of a way to calculate average speed from what I have. Is there a formula that lets me do that?

This meets almost all the expectations we have of a homework-like question:

• It quotes the original problem
• It shows some work (organizing the given values, calculating total distance and time and the speed in each segment)
• It asks a question, "Is there a formula that lets me do that?", which is

• specific, i.e. not asking for the answer to the problem, nor asking for "help" in general, but asking for a way to get through the single step that the asker is stuck on
• conceptual, i.e. not asking us to do a calculation nor to come up with a whole chain of reasoning out of thin air

However, this question still falls short of being really acceptable in one significant way: the asker didn't didn't do their research. At a minimum, we would expect an asker to check a textbook or do a web search to look up information about key concepts involved in the problem, in this case "average speed", and the top search result for "average speed" (at least for me) is https://www.wikihow.com/Calculate-Average-Speed, which gives step-by-step instructions for calculating the average speed. If the asker had done that search before posting, they should have found that page or something like it and at least tried to apply the instructions there. The fact that they didn't mention trying that, and in fact didn't even mention finding that web page, means they didn't do enough research.

I think in this case there is no way to ask the question in a way that would be acceptable on this site - at least, not as long as the thing keeping you from solving the problem is that you don't know the formula. It's simply too easy to look that up. But in general, many homework-like problems are more complicated than this, and there isn't such an easy path to looking up the answer or a procedure for finding it. In those cases, you can search the web, check textbooks, go through some preliminary calculations, and try to make progress on the problem in other ways, and still be left with some conceptual issue, smaller than the whole problem, which you're unable to figure out - and that's what can make a good question here.

Since it seems to be a frequent point of confusion for many people, let me say clearly: the fact that a question does not include numerical values does not make it conceptual. Even the fact that a question does not ask us to do a calculation of any sort, does not make it conceptual, although that comes a bit closer.

• I see you're going for the Freehand Circle hat there. – Emilio Pisanty Dec 12 '18 at 11:02
• I deleted a comment bc I didn't read far enough into the post. – Kyle Kanos Dec 12 '18 at 18:35
• @KyleKanos Fair enough :) I saw the comment, it did make a good point. – David Z Dec 12 '18 at 18:51
• @DavidZ Hi there! I'm still unable to get your answer whether positive or negative against homework policy. So, can't we request conceptual step? – Busi Dec 12 '18 at 19:02
• @Busi I don't understand what you mean there. Why do you say "positive or negative against homework policy"? My answer is not about whether or not I like the homework policy, it's about how you could change your sample question to be more in line with the homework policy. Also, what do you mean by "can't we request conceptual step?" The answer to that depends on what you mean. You can generally ask conceptual questions about a single step in solving the problem, but that's not the same as asking for a step to be given to you. – David Z Dec 12 '18 at 19:54
• @DavidZ What I mean is, can anyone post their homework questions without providing any value? "X: A straight line carrying a uniform linear charge density μC/m is stretched along the z-axis. How would a physicist apply gauss law to find the field at a distance of m from the wire?" He also shows his researches in textbooks or anywhere. In this case, he did not provide any specific value or computation. Could you rate this comment? – Busi Dec 13 '18 at 13:26
• @Busi the question you propose in the comment above would also violate the HW policy because it's asking for a calculation (even with no values given, it's still a calculation). – Kyle Kanos Dec 13 '18 at 18:28
• @KyleKanos Not really, then the policy does not truly make any sense. – Busi Dec 13 '18 at 18:34
• @Busi I don't think it's confusing policy, I think you're just unsure what conceptual means. Asking us to do math (algebraic or numeric) is generally considered off-topic because they aren't concepts. – Kyle Kanos Dec 13 '18 at 18:38
• Yep, though I would add that just because a question doesn't ask us to do math, that doesn't make it conceptual. – David Z Dec 17 '18 at 3:02

Question statement:

A straight line carrying a uniform linear charge density $$4\mu C/m$$ is stretched along the $$z$$-axis. Apply Gauss' law to find the field at a distance of $$1m$$ from the wire?

Non-conceptual question: How to I apply Gauss's law for this problem?

Conceptual question: I know that Gauss' law for this case requires the use of a cylinder. But how can the cylinder be chosen to have finite length $$\ell$$ when the line of charges extends from $$-\infty$$ to $$\infty$$? The same type of question arises for the case of an infinite plane with constant surface charge density: why can we choose a Gaussian cube of finite size when the charges extend to infinity in the plane?

In the second case, the question is about the process and the assumptions that go into using Gauss' law, whereas in the first it's about the answer.

• Ooh, yes I like this example. – David Z Dec 13 '18 at 1:38
• What I mean is, can anyone post their homework questions without providing any value? "X: A straight line carrying a uniform linear charge density μC/m is stretched along the z-axis. How would a physicist apply gauss law to find the field at a distance of m from the wire?" He also shows his researches in textbooks or anywhere. In this case, he did not provide any specific value or computation. – Busi Dec 13 '18 at 5:41
• @Busi I don't think "how to apply Gauss' law to find the field" is conceptual. It's asking someone to do the work for you. – ZeroTheHero Dec 13 '18 at 13:28
• @ZeroTheHero However, you don't do any specific calculations. – Busi Dec 13 '18 at 13:29
• @Busi while I certainly think that removing numbers is a first step (although the statement of my example question does have numbers), I would also expect the OP to show some effort towards the solution. For instance: "I can use $S=\frac{\Delta x}{t}$ but if I integrate $\int dx$ over the time of the motion I do not get the same result." – ZeroTheHero Dec 13 '18 at 13:41
• @ZeroTheHero Assume that OP showed sufficient effort towards the solution and is not providing any values, would that question be welcome? – Busi Dec 13 '18 at 13:43
• @Busi Your looking for a clear line where there isn’t one. After all it takes 5 votes to close. What you suggest would be more favorably looked upon, but no guarantees. And please be aware that my opinion is my own and others may have a different threshold. The comments of DavidZ are very relevant. – ZeroTheHero Dec 13 '18 at 15:27

A good conceptual question is one where the questioner outlines the thought process that leads to an impasse. @ZeroTheHero gave one good example of this.

A good answer to a conceptual question is one that lifts the impasse without giving out the solution.