User talk:J Doug McLean/sandbox

I see problems with some of the expressions used. They make the article look like it is written for a very young audience. They don’t seem appropriate in an encyclopedia. I have selected three:

The flow above the upper surface is always speeded up, and the flow below the airfoil is usually slowed down.

speeded up and slowed down are not particularly appropriate in a scientific article in an encyclopedia.

But this cause-and-effect relationship is not a one-way street.

This is colloquial. Its meaning is likely to be known only to the author.

The pressure difference can exist only if it has something to push against.

What is the origin of this statement? It is not a scientific principle. Pressure differences are at the heart of the scientific principle known as Bernoulli’s principle but this statement does not come from Bernoulli's principle, nor is it consistent with Bernoulli's principle. Dolphin (t) 06:09, 6 April 2013 (UTC)[reply]

Thanks for the interesting comments. I'm not sure I agree with the first two style comments. To me, these passages sound like they were written for a literate, non-specialist audience, not a very young audience. But I'll consider making changes.

The third item is definitely based on a scientific principle. It's not Bernoulli's principle; it's Newton's third law. If there is a pressure difference between two points in space, then the pressure gradient must be non-zero over some extent of the intervening space. Any fluid parcel immersed in this pressure gradient has a net pressure force exerted on it in the direction down the gradient. According to the third law, the parcel must push back, which is the basis of my statement that a pressure difference requires a push-back. In an inviscid flow, this force exchange (push and push-back) requires acceleration of the fluid parcel. So, what the passage says is true and is based on a real scientific principle. Perhaps there is a clearer way to say it, for example: "In a flowing fluid, a pressure difference can exist only if something else is happening in the flow so as to push back against the pressure difference, as required by Newton's third law." J Doug McLean (talk) 17:02, 30 April 2013 (UTC)[reply]

As you know, anything on Wikipedia that is challenged, or likely to be challenged, must be attributed to a reliable published source to allow independent verification. (See WP:V) Your paragraph immediately above suggests that you have started with Newton's third law, a concept that can be attributed to any one of a large number of reliable sources, then interpreted it to be described as 'a pressure difference can only exist where it has something to push against etc.' and supported your description by an erudite argument that shows your interpretation must be correct. Unfortunately, technical argument of that kind, even though it is entirely defensible in any scientific forum, doesn't alter the fact that, for Wikipedia's purposes, your description is original research. Wikipedia doesn't publish original research, or even original thought. Therefore, if our article is to contain a statement about pressure differences needing something to push back against, it must be supported by citation of a reliable, published source - an erudite argument by the author is not sufficient. Unless you can cite a reliable published source that talks about pressure differences needing something to push back against, that statement shouldn't be inserted into the article. Alternatively, raise the matter on the relevant Talk page and see what other interested Users think of it. Regards. Dolphin (t) 23:45, 30 April 2013 (UTC)[reply]

This could be a problem. In the lift explanation in my book (a citable source) I made the same statement you quote in your third bullet above, and I did not back it up by explicitly linking it to Newton's third law because I assumed that went without saying. So the original statement has a citable source (my book), but I don't know of one for the more explicit version of it. The "more comprehensive" lift explanation in my sandbox would probably still work with that statement deleted. Or I suppose the statement in its original form is formally "verifiable". I'll think about it. Regards, J Doug McLean (talk) 04:15, 8 May 2013 (UTC)[reply]

July 2021[edit]

Hi Doug. I stumbled on your work in your sandbox, and had a quick look at it. My initial reaction is that it looks very much like a PhD thesis or student essay. It doesn't look like an entry for an encyclopaedia. (I'm sure you are aware that Wikipedia is not an essay or a text book. Regards, Dolphin (t) 13:34, 31 July 2021 (UTC)[reply]