User talk:Mr swordfish/sandbox

Simplified explanations of lift

Thanks for doing this work and giving interested Users the opportunity to peruse it and provide feedback.

Your version looks good. I draw attention to Doug McLean’s sentence “This explanation is correct as far as it goes but is incomplete.” I think the expression “as far as it goes” is colloquial; it should be replaced with something more encyclopaedic.

When a sentence ends with one or more citations it is custom to end the sentence with a period, and then have the citations follow the period. In the majority of such cases in your sandbox, the citations are located between the last word and the period. Dolphin (t) 13:23, 20 August 2021 (UTC)[reply]

I had the convention backwards for where the period goes, and was careful to always put the refs before the period. I'll change that.

"As far as it goes" may well be colloquial. I'm at a loss for better verbiage, but the article seems to read adequately well if that phrase is removed:

This explanation is correct but it is incomplete. It doesn't explain how the airfoil can impart downward turning to a much deeper swath of the flow than it actually touches. Furthermore, it doesn't mention that the lift force is exerted by pressure differences, and doesn't explain how those pressure differences are sustained.

Mr. Swordfish (talk) 14:31, 20 August 2021 (UTC)[reply]

I agree that it reads "adequately well" with the phrase removed, but it doesn't mean quite the same thing. My vote is to keep the phrase. J Doug McLean (talk) 23:26, 20 August 2021 (UTC)[reply]

Yes, it doesn't read the same. My preference is to keep it as well. What I am unsure about is how "nonstandard" or "colloquial" the phrase is. As someone who grew up speaking US English, I am often unaware of how many phrases we use on a daily basis are actually idioms rather than "standard English". Is this one? Not sure - but even a non-native English speaker should be able to impute what it means since it's not that hard to parse its meaning. So I think it's ok (another colloquialism) to keep it. Curious to see what our antipodal editor has to say about it. Dolphin? Mr. Swordfish (talk) 00:20, 21 August 2021 (UTC)[reply]

The expression “as far as it goes” is indeed colloquial; it is a collection of redundant words, a mannerism of those who use it regularly. It is informal language that is used spontaneously in speech and carelessly in writing, but not in formal language of the kind used in professional writing and expository texts. Its intended meaning cannot be determined accurately by unpacking the words and examining them carefully: “correct as far as it goes” leaves the following questions unanswered:

How far DOES it go?
What happens if it goes farther than it should – does [the explanation] become incorrect?

The objective of the paragraph in question appears to be to support the stated theme that each of the simplified explanations of lift is incomplete in some way. This is a valid objective and I’m sure it can be achieved using formal, encyclopaedic language. I will give some suggested text at the end of this post.

In physics it is a common fact, perhaps a universal fact, that no explanation of a phenomenon is complete. This never detracts from the status of the physics law or principle being used to make an explanation. For example, the Earth exerts a force of attraction on the Moon, and the Moon exerts an identical force on the Earth, and this is explained by Newton’s third law, but that law doesn’t explain WHY each of these bodies exerts any force at all on the other; to explain that, we must use a different law – Newton’s law of universal gravitation. I seriously doubt that any reliable published source has ever stated, in relation to celestial mechanics, that Newton’s third law is correct but it is not completely correct because it fails to answer another important question we might have on the subject. Similarly, we regularly use the first and second law of thermodynamics but I doubt that any professional writer would suggest that the need for two laws, instead of just one, is a disappointment and shows that each law is somehow flawed in its scope until someone can devise One Big Law of Thermodynamics.

The suggested text includes “It doesn't explain how the airfoil can impart downward turning to a much deeper swath of the flow than it actually touches.” It doesn’t explain anything about how the airfoil can impart downward turning; not just “to a much deeper swath …”

I offer the following text for consideration:

Flow deflection combined with Newton’s laws is a helpful way to explain some aspects of lift. It leaves some questions unanswered; it doesn't explain how the airfoil imparts downward turning to the flow, and it doesn't mention that the lift force is exerted by pressure differences. It doesn't explain how those pressure differences are sustained.

Dolphin (t) 13:34, 21 August 2021 (UTC)[reply]

As readers start on this topic they see:

"But simplifying the explanation of lift is inherently problematic, and all of the known simplified explanations leave significant parts of the phenomenon unexplained and have other significant flaws."

Five short paragraphs later readers see:

"This explanation is correct as far as it goes but is incomplete."

These two sentences seem to be saying the same thing. I think the first sentence presents the idea well and applies it to simplified explanations generally, and the second sentence just presents the same thing but specifically targeted at the Newton explanation. I don't see that anything is achieved by duplicating the sentiment - it looks like the two sentences were written by different Users or at different times so the duplication was not noticed.

In-line citations 1, 23 - 27, and 35 - 39 are located between the last word and the period. Dolphin (t) 12:55, 26 August 2021 (UTC)[reply]

What is currently in my sandbox is the latest version from Doug McLean. I have not yet merged his latest version with my latest version. It does sound like you are now in favor of keeping the opening section so I'll retain it in the merge. Hopefully, the merge will address your concerns. Mr. Swordfish (talk) 14:30, 26 August 2021 (UTC)[reply]

Misunderstandings about the generation of lift

Thanks for your contribution to improving this section. I can make some suggestions.

The first sentence: "Bernoulli's principle is often used to explain aerodynamic lift, the force that allows fixed-wing aircraft to fly" appears not to lead logically into the sentences that follow. I suggest this sentence be removed, leaving the text as follows. (My additions and changes are bolded):

One of the most common explanations of aerodynamic lift asserts that the air must traverse the upper and lower surfaces of a wing in the same amount of time, implying that since the upper surface presents a longer path the air must be moving faster over the top of the wing than the bottom. Bernoulli's principle is then cited to conclude that the pressure must be lower on top of the wing than the bottom.

However, there is no physical principle that requires the air to traverse the upper and lower surfaces in the same amount of time. In fact, theory predicts and experiments confirm that the air traverses the top surface in a shorter time than it traverses the bottom surface, and the explanation based on equal transit time is false. It is not the Bernoulli principle itself that is false, because this principle is well established; Bernoulli's equation is commonly used correctly in mathematical treatments of aerodynamic lift.

Happy to discuss further. Dolphin (t) 12:57, 8 April 2022 (UTC)[reply]

I've implemented your suggestions. Do we need to say anything else in this section? We could go on for several pages, but I'm inclined to keep it short since this article is not about lift. Mr. Swordfish (talk) 13:14, 8 April 2022 (UTC)[reply]

I think this is sufficient. I agree that this is only a minor part of the story of Bernoulli’s principle so it should be kept short. Dolphin (t) 14:05, 8 April 2022 (UTC)[reply]

I've added some citations, so it's ready to be published. I'll give it a day or so to give other editors a chance to weigh in. Mr. Swordfish (talk) 19:15, 8 April 2022 (UTC)[reply]

You say "... inferring that since the upper surface presents a longer path the air must be moving faster over the top of the wing than the bottom." Inferring should be implying. Dolphin (t) 12:14, 10 April 2022 (UTC)[reply]

Draft amendments to Magnus effect

So far I have noticed a few things to draw to your attention. These are not necessarily problems introduced by you recently - they may have existed in the article for a long time.

In one image caption it says Air is carried around the object in the boundary layer, this adds to the velocity of the airstream above the object and subtracts below resulting in increased airspeed above and lowered airspeed below. This is two sentences. I think the comma should be replaced by a period.

Here, and possibly in another one or more places, it says Air is carried around the object in the boundary layer. The depth of the boundary layer (BL) is minuscule and so is the mass of air in it. Magnus effect requires a much greater mass of air to be involved in the phenomenon of “faster on one side; slower on the other.” The shear force between the outer surface of the BL and the inner surface of the irrotational flow beyond the BL has the effect of accelerating the irrotational flow in one region, and decelerating it in the opposite region. It is as though the BL has many tentacles that reach out into the irrotational region and try to make it match the speed of the BL. Any change in velocity quickly (instantly?) resolves into the regime of a free vortex in which speed v is inversely proportional to distance from the center r of the vortex. As a result, the entire irrotational region, not just the BL, develops a circulation (Gamma) that can be used in the Kutta- Joukowsky theorem.

In at least one place there is a statement that the BL is more violent on one side than the other. “Violent” is not a word applied to the BL. Magnus effect does not rely on violence, or otherwise, in the BL. It relies on the pressure in the BL. Dolphin (t) 14:40, 21 September 2024 (UTC)[reply]

1) I'll replace the comma with a period in the draft.

2) Agree that the boundary layer is small and that the momentum change is mostly due to the air outside the boundary layer. I 'll try to come up with simply-worded alternative language that avoids this issue.

3) I didn't know what to make of that sentence so I left it as-is. Agree that it is problematic. I'll take a look at refining it, or perhaps just removing it.

Thanks for your helpful comments. Mr. Swordfish (talk) 15:15, 21 September 2024 (UTC)[reply]

Since you kindly pasted my draft "Magnus effect in potential flow" I have made 7 edits to the draft (in my sandbox) - the first one on 19 September at 23:55 hours. They are useful but not Earth shattering. I recommend you peruse the changes and update the text in your sandbox.

Thanks for preparing your draft and offering it for comment. I have no further suggestions so I'm happy if you launch your version into mainspace. Dolphin (t) 13:43, 22 September 2024 (UTC)[reply]

I've updated that section to include your recent changes, and will update the main space article. There's still a bit or work to do on the article, but this seems to be a step forward. Mr. Swordfish (talk) 14:21, 22 September 2024 (UTC)[reply]