Talk:3090: Sail Physics - Revision history

162.158.216.191 at 15:00, 19 May 2025

2025-05-19T15:00:11Z

162.158.216.191 at 14:57, 19 May 2025

2025-05-19T14:57:55Z

StapleFreeBatteries at 23:47, 18 May 2025

2025-05-18T23:47:49Z

StapleFreeBatteries at 23:47, 18 May 2025

2025-05-18T23:47:25Z

StapleFreeBatteries at 23:21, 18 May 2025

2025-05-18T23:21:15Z

162.158.74.14 at 17:50, 18 May 2025

2025-05-18T17:50:08Z

RegularSizedGuy at 16:52, 18 May 2025

2025-05-18T16:52:52Z

JimJJewett: answered Qs about why the typical explanation is "wrong", and whether such sailboats exist

2025-05-18T06:41:01Z

answered Qs about why the typical explanation is "wrong", and whether such sailboats exist

172.68.205.187 at 00:24, 18 May 2025

2025-05-18T00:24:15Z

172.71.142.188: Solar sails, magnetic sails, sailing upwind with solar

2025-05-17T23:40:16Z

Solar sails, magnetic sails, sailing upwind with solar

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 After the last step, the sailors would then need to ground the boat to avoid being pushed in a circle, wouldn't they? [[User:Sophon|Sophon]] ([[User talk:Sophon|talk]]) 20:47, 16 May 2025 (UTC)
 Note that for eastward wind, the boat will be propelled upwards, while the opposite is true for westward winds. This provides a basis for the functioning of airships and planes (Helicopters are more complicated, and additionally rely on their own magnetic fields) [[Special:Contributions/162.158.217.45|162.158.217.45]] 21:21, 16 May 2025 (UTC)

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 Is this actually wrong? Wouldn't it still be ''a'' force on a sailboat, even if it's not the strongest? [[User:Smurfton|Smurfton]] ([[User talk:Smurfton|talk]]) 22:20, 16 May 2025 (UTC)
 : I added some explaination on direction and magnitude of the lorentz force, maybe that will help - sga {{unsigned ip|172.68.234.227|22:33, 16 May 2025 (UTC)}}
 : Yeah, is it more or less effective than the kedging cannon? [[User:StapleFreeBatteries|StapleFreeBatteries]] ([[User talk:StapleFreeBatteries|talk]]) 23:47, 18 May 2025 (UTC)
 The explanation states that of the four forces, only the electromagnetic force operates at the macro level. This is incorrect, as gravity is also directly observable by humans. There should also probably be a link to https://en.wikipedia.org/wiki/Airfoil to provide an explanation for how sails actually allow a boat to sail upwind. I recommend removing the remark about the poles potentially flipping in the future, as this is irrelevant. [[Special:Contributions/172.68.55.124|172.68.55.124]] 23:52, 16 May 2025 (UTC)
 : What i meant was, for 2 objects at scales of humans =, maybe did not prase it well. In this case, it is the wind and the sail. Wind does not have a "mass" (the atoms most certainly do, but) we essentially have a pressure force, or momentum of wind, where instead of using the energy of atoms (and hence the mass) as given by kinetic theory is not used (that is random (as given by boltzman maxwell statistics)) and uniform (in the sense that for any direction, number of particles going against and towards is equal) and what we have is just pressure applied by a effective "group velocity" of the wind atoms. The gravity interaction between wind and boat, or the local waves and boat is negligible, and planetary  gravity is not considered because that is not relavant for in plane motion. the pole fillping was added just for future proofing the article. I am sorry for the puns. I have rewwritten some parts, and reduced the part about pole flipping, and also added the average case scenario for the force, hope it is better now. - sga {{unsigned ip|172.70.143.75|02:37+, 17 May 2025}}
 ::That is one huge rambling paragraph, if it's (mostly) yours. I'm no stranger to ''writing'' huge rambling paragraphs, myself, but I gave up only a little way in on trying to make it read better. Grammatically, prosaically and with relevence.
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 In the example - somebody should recheck the math (I just copied what there, but in changing units to be more familiar, like km/h, I might have introduced errors).  I also changed the field strength to the right order of magnitude for Earth's surface, and multiplied the wind speed by 10 to compensate.
 As best I can figure the numbers for the example may have been chosen to get a force of 1 Newton.  (I can't see any other reason for the ludicrous wind speed of thousands of km/h.)  Might be better example to use a reasonable wind speed (e.g. dial it back to hurricane force) and a reasonable charge (something like what you could accumulate with an automobile, or when you zap yourself after getting out of a car seat) wind up with an even more negligible force.  Then we could dispense with the paragraph explaining why 1 Coulomb is silly. [[Special:Contributions/172.71.151.93|172.71.151.93]] 22:15, 17 May 2025 (UTC)
 :If anybody wants to restore parts of it or play with it, the version with the calculation of Lorentz forces is here [https://www.explainxkcd.com/wiki/index.php?title=3090:_Sail_Physics&oldid=378099]  I thought it somewhat interesting just as physics problem to show what the effect was.
 :I got curious about how much charge is involved when one zaps oneself on a car seat.  A lighting bolt is a few coulombs.  [[Special:Contributions/172.71.142.188|172.71.142.188]] 23:40, 17 May 2025 (UTC)
 Extreme apologies to an(other) IP editor who may have made several possibly great improvements to the article. I had ''so'' many problems with what was already there that I did a massive rewrite and set things up so differently that I'm not sure that (at a very long glance, but maybe not as long as it diserves) much of that effort is really worth feeding back in. Or even capable of being. Obviously, it's up to the rest of the you (including the person/people I overrode) to make your own judgement about that. I will also go back in to carefully check what I may have desecrated. [[Special:Contributions/162.158.74.68|162.158.74.68]] 22:37, 17 May 2025 (UTC)
 :No problem.  I remade a few tweaks.  The calculation is linked above is anybody wants to restore part of it.  [[Special:Contributions/172.71.142.188|172.71.142.188]] 23:40, 17 May 2025 (UTC)
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 I just mention here in case anybody thinks way makes sense in comic explanation.  [[Special:Contributions/172.71.142.188|172.71.142.188]] 23:40, 17 May 2025 (UTC)
 :Well, if you send charge along a long conductor (which might be what you do if you're sending/receiving the sail-charge through the thing that the sail is attached to the payload with), ''and'' pass through any magnetic fields (planetary, solar... galactic?) then you're into the territory of the {{w|Electrodynamic tether}} as ''also'' useful for propulsion. [[Special:Contributions/172.68.205.187|172.68.205.187]] 00:24, 18 May 2025 (UTC)
 Related to the question of how sails might work (against the wind), and the relationship to wing effects, I'm reminded of how a {{w|Cabin Pressure (radio series)|comedy radio sitcom}} dealt with the wings thing. In case it's not quickly obvious (and with some non-obvious info added), characters are Arthur ('simple' but questioning Air Steward), Carolyn (his mother, bossy owner of the airplane and chief Air Steward/everything else that's not actually flying), Martin (chief pilot/captain, knowledgable but inexperienced) and Douglas (second in command, but senior in years and experience and 'street smart'/air-smart to the point of (usually well-deserved) smugness).
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 {{cob}}
 ...just thought anyone who hadn't heard this (or had, but liked the comedy involved) might like to read it. [[Special:Contributions/172.68.205.187|172.68.205.187]] 00:24, 18 May 2025 (UTC)
 :Sounds like comic 803. [[User:StapleFreeBatteries|StapleFreeBatteries]] ([[User talk:StapleFreeBatteries|talk]]) 23:21, 18 May 2025 (UTC)

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 : I added some explaination on direction and magnitude of the lorentz force, maybe that will help - sga {{unsigned ip|172.68.234.227|22:33, 16 May 2025 (UTC)}}
-: Yeah, is it more or less effective than the kedging cannon?
+: Yeah, is it more or less effective than the kedging cannon? [[User:StapleFreeBatteries|StapleFreeBatteries]] ([[User talk:StapleFreeBatteries|talk]]) 23:47, 18 May 2025 (UTC)
 The explanation states that of the four forces, only the electromagnetic force operates at the macro level. This is incorrect, as gravity is also directly observable by humans. There should also probably be a link to https://en.wikipedia.org/wiki/Airfoil to provide an explanation for how sails actually allow a boat to sail upwind. I recommend removing the remark about the poles potentially flipping in the future, as this is irrelevant. [[Special:Contributions/172.68.55.124|172.68.55.124]] 23:52, 16 May 2025 (UTC)

@@ Line 8: / Line 8: @@
 : I added some explaination on direction and magnitude of the lorentz force, maybe that will help - sga {{unsigned ip|172.68.234.227|22:33, 16 May 2025 (UTC)}}
 The explanation states that of the four forces, only the electromagnetic force operates at the macro level. This is incorrect, as gravity is also directly observable by humans. There should also probably be a link to https://en.wikipedia.org/wiki/Airfoil to provide an explanation for how sails actually allow a boat to sail upwind. I recommend removing the remark about the poles potentially flipping in the future, as this is irrelevant. [[Special:Contributions/172.68.55.124|172.68.55.124]] 23:52, 16 May 2025 (UTC)
@@ Line 125: / Line 127: @@
 ...just thought anyone who hadn't heard this (or had, but liked the comedy involved) might like to read it. [[Special:Contributions/172.68.205.187|172.68.205.187]] 00:24, 18 May 2025 (UTC)
-:Sounds like comic 803
+:Sounds like comic 803. [[User:StapleFreeBatteries|StapleFreeBatteries]] ([[User talk:StapleFreeBatteries|talk]]) 23:21, 18 May 2025 (UTC)

← Older revision		Revision as of 23:21, 18 May 2025
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	...just thought anyone who hadn't heard this (or had, but liked the comedy involved) might like to read it. [[Special:Contributions/172.68.205.187\|172.68.205.187]] 00:24, 18 May 2025 (UTC)		...just thought anyone who hadn't heard this (or had, but liked the comedy involved) might like to read it. [[Special:Contributions/172.68.205.187\|172.68.205.187]] 00:24, 18 May 2025 (UTC)
		+
		+	:Sounds like comic 803
		+	[[User:StapleFreeBatteries\|StapleFreeBatteries]] ([[User talk:StapleFreeBatteries\|talk]]) 23:21, 18 May 2025 (UTC)

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 The picture seems to show an axis of rotation (the mast) for the sail being on the end of the sail. Is that correct for a certain class of sailing vessel?~~ {{unsigned ip|162.158.146.128|15:57, 17 May 2025}}
 :Yes.  Though offhand, I can't think of a ''good'' sailboat ''with only 1 sail'' where it was true beyond a first approximation. [[User:JimJJewett|JimJJewett]] ([[User talk:JimJJewett|talk]]) 06:41, 18 May 2025 (UTC)
 Currently the explanation says "most interaction of physical things at macro scale (humans and boat sized objects) are electromagnetic in nature"  I have certainly read that, and have seen examples of electromagnetic interactions between atoms.  However, I also encounter explanations that describe interactions in terms of Pauli exclusion principle (see for instance {{w|Contact force}}).  This makes me question the view presented in the first sentence.  Since my physics is a bit rusty I haven't tried to fix it, but I think it may need clarification.  [[Special:Contributions/172.71.150.33|172.71.150.33]] 20:28, 17 May 2025 (UTC)

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 :You aren't alone - I think I was an adult before I understood tacking in the sailboat sense of the word. [[Special:Contributions/162.158.174.127|162.158.174.127]] 02:45, 17 May 2025 (UTC)
 : I'm wanting to add in some wisdom about "science-y" explanations that appear to be sensible but are completely wrong, segueing into how generative language models appear to be far more reliable than they are. However this margin is too narrow [[User:Kev|Kev]] ([[User talk:Kev|talk]]) 03:09, 17 May 2025 (UTC)
 I've been really annoyed with ExplainXKCD in the last few months ever since the initial posting has always been LLM generated. It requires more brain power to make sense of AI slop and edit it, than to contribute to a blank page. [[Special:Contributions/162.158.162.103|162.158.162.103]] {{unsigned ip|162.158.162.103|15:44, 17 May 2025|...yes, probably signed with just three tildes, by accident, but the intended message is the same...}}

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 The joke is that the most commonly used explanation for why flow over a foil generates lift - particles going one way have a longer way to travel than the other, which generates a difference in speed and therefore a pressure differential - is wrong. {{unsigned ip|172.69.109.91|10:36, 17 May 2025}}
 :What is wrong with the explanation which you say is wrong?  What is the more correct explanation?  [[Special:Contributions/172.71.150.33|172.71.150.33]] 20:28, 17 May 2025 (UTC)
 The picture seems to show an axis of rotation (the mast) for the sail being on the end of the sail. Is that correct for a certain class of sailing vessel?~~ {{unsigned ip|162.158.146.128|15:57, 17 May 2025}}
 Currently the explanation says "most interaction of physical things at macro scale (humans and boat sized objects) are electromagnetic in nature"  I have certainly read that, and have seen examples of electromagnetic interactions between atoms.  However, I also encounter explanations that describe interactions in terms of Pauli exclusion principle (see for instance {{w|Contact force}}).  This makes me question the view presented in the first sentence.  Since my physics is a bit rusty I haven't tried to fix it, but I think it may need clarification.  [[Special:Contributions/172.71.150.33|172.71.150.33]] 20:28, 17 May 2025 (UTC)

← Older revision		Revision as of 00:24, 18 May 2025
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	One question I haven't found anything about is do solar sails (conventional ones, not electric) accumulate charge, and what effects that might have.		One question I haven't found anything about is do solar sails (conventional ones, not electric) accumulate charge, and what effects that might have.
	I just mention here in case anybody thinks way makes sense in comic explanation. [[Special:Contributions/172.71.142.188\|172.71.142.188]] 23:40, 17 May 2025 (UTC)		I just mention here in case anybody thinks way makes sense in comic explanation. [[Special:Contributions/172.71.142.188\|172.71.142.188]] 23:40, 17 May 2025 (UTC)
		+	:Well, if you send charge along a long conductor (which might be what you do if you're sending/receiving the sail-charge through the thing that the sail is attached to the payload with), ''and'' pass through any magnetic fields (planetary, solar... galactic?) then you're into the territory of the {{w\|Electrodynamic tether}} as ''also'' useful for propulsion. [[Special:Contributions/172.68.205.187\|172.68.205.187]] 00:24, 18 May 2025 (UTC)
		+
		+
		+
		+	Related to the question of how sails might work (against the wind), and the relationship to wing effects, I'm reminded of how a {{w\|Cabin Pressure (radio series)\|comedy radio sitcom}} dealt with the wings thing. In case it's not quickly obvious (and with some non-obvious info added), characters are Arthur ('simple' but questioning Air Steward), Carolyn (his mother, bossy owner of the airplane and chief Air Steward/everything else that's not actually flying), Martin (chief pilot/captain, knowledgable but inexperienced) and Douglas (second in command, but senior in years and experience and 'street smart'/air-smart to the point of (usually well-deserved) smugness).
		+
		+	{{cot\|Excerpt dialogues from Cabin Pressure, series(/season) 1, episode 1}}
		+	:[Arthur:] No, never! It’s just always exciting! That amazing moment when twelve tons of metal leaves the earth – and no-one knows why!
		+	:[Carolyn:] Yes, we do.
		+	:[Arthur:] Yeah, but ...you know, not really. I mean, we know you need wings and engines and a ...sticky-up bit on the end for some reason, but it’s not like we actually know why a plane stays in the air.
		+	:[Carolyn:] No, no, Arthur, we really do. We-we do, we do know that.
		+	:[Arthur:] Oh! How, then?
		+	:[Carolyn:] Well ...er, because...
		+	:[...some minor diversionary tactics break the conversation all too briefly...]
		+	:[Carolyn:] Because there are four forces acting on the plane, and so long as two of them are bigger than the other two, the plane flies.
		+	:[Arthur:] ...Mum, I don’t mind that no-one knows.
		+	:[Carolyn:] But we do! We do! That’s it! What I said: that’s how.
		+	:[Arthur:] Well, what are the four forces, then?
		+	:[Carolyn:] Yes! Well, I will tell you what they are. Lift ...weight ...er...
		+	:[Arthur:] Up and down?
		+	:[Carolyn:] No, no, no, no, no. Tho-Those are up and down. No, it’s lift, weight...
		+	:[Arthur:] Left and right.
		+	:[Carolyn:] No, no, no, no. Lift, weight...
		+	:[Arthur:] En...gines?
		+	:[Carolyn:] No, no ...well, yes, yes, yes, sort of. Um, thrust, thrust. Lift, weight, thrust and...
		+	:[Arthur:] Time.
		+	:[Carolyn:] Drag. Lift, weight, thrust and drag. So, the weight and drag are overcome because the engines give the plane thrust, and the wings give it lift. And that’s how a plane flies.
		+	:[Arthur:] How do the wings give it lift?
		+	:[Carolyn:] What?
		+	:[Arthur:] The wings are really heavy. How does bolting two ginormous lumps of metal to a ginormous lump of metal give it lift?
		+	:[Carolyn:] Well, because they are wings. Well, they’re like birds’ wings.
		+	:[Arthur:] Yeah, but birds’ wings flap. Ours don’t flap. They’ve got flaps, but I once watched the flaps all the way to Stockholm and, take it from me, they are seriously mis-named. So-so why does having wings make a plane leave the runway?
		+	:[conveniently timed distraction occurs to take Carolyn away...]
		+	:[Arthur:] Yeah, but how do the wings...
		+	:[...letting the conversation and action move on, until...]
		+
		+	:[Douglas:] And now it’s back to the boring old plane flying.
		+	:[Arthur:] Oh, yes. About that. Um, I wanted to ask you something, Skipper. Mum was telling me this morning that planes fly because they’ve got wings.
		+	:[Douglas:] Is there anything that woman doesn’t know?
		+	:[Arthur:] But she didn’t really explain – why do wings lift us up?
		+	:[Douglas:] Ah, well. Essentially...
		+	:[Martin:] Uh, Douglas, he asked me. Listen carefully, Arthur. The wing is curved on top but flat on the bottom. When it meets the air, it splits it in two. The air that goes over the top has further to go, so it has to go faster to keep up with the air underneath. That reduces the pressure above the wing, giving us lift.
		+	:[Arthur:] Ah, fantastic! Thanks, Skipper! I totally get it now.
		+	:[Martin:] You’re welcome.
		+	:[Arthur:] Except ...why does it have to?
		+	:[Martin:] Why does what what?
		+	:[Arthur:] Why does the air on the top have to keep up with the air on the bottom? Why don’t they just split up?
		+	:[pause]
		+	:[Douglas:] ...for the sake of the kids?
		+	:[action moves on again, until...]
		+
		+	:[...they need to distract Arthur from ''something else'']
		+	:[Douglas:] Arthur, you were asking why the air over the wing has to keep up with the air underneath.
		+	:[Arthur:] Ooh, yes. Do you know?
		+	:[Douglas:] Indeed I do. Attend: the air is not passing over the wing; the wing is passing through the air, so the curved upper side stretches the air forced over it apart, reducing pressure, producing lift. The lift pushes up; the weight pushes down – so as long as the lift is more than the weight, up we go. And that, my friend, is how an aeroplane flies.
		+	:[Arthur:] Got it! Right, yes! Cracking! I completely get it now.
		+	:[Douglas:] Good. You see, it’s actually quite easy to grasp when it’s explained properly by someone who understands...
		+	:[Arthur:] So that’s why planes can’t fly upside down.
		+	:[Douglas:] Er, yes they can.
		+	:[Arthur:] Can they?
		+	:[Douglas:] Well, of course they can. Haven’t you seen the Red Arrows?
		+	:[Arthur:] But ...doesn’t that mean the curved side of the wing is on the bottom, so the lift is pushing down as well as the weight? How does that work?
		+	:[Martin:] Yes, Douglas. How does that work?
		+	:[Douglas:] Well, Arthur, there’s a very simple explanation; but just to finish what we were saying, Martin...
		+	[...the ''something else'' is raised as a distraction from the question]
		+	:[Douglas:] No-one wants to hear the explanation. What a shame.
		+	{{cob}}
		+	...just thought anyone who hadn't heard this (or had, but liked the comedy involved) might like to read it. [[Special:Contributions/172.68.205.187\|172.68.205.187]] 00:24, 18 May 2025 (UTC)