Talk:620: Wings - Revision history

Conjuncts: Commentary on belay equipment

2025-07-24T04:03:13Z

Commentary on belay equipment

42.book.addict at 18:29, 5 November 2024

2024-11-05T18:29:49Z

172.70.111.34: Just some niggling thoughts I had.

2024-10-05T16:18:04Z

Just some niggling thoughts I had.

Obscure xkcd reference at 13:47, 13 November 2021

2021-11-13T13:47:50Z

141.101.104.44 at 17:00, 8 September 2016

2016-09-08T17:00:27Z

Weatherlawyer at 01:21, 29 January 2015

2015-01-29T01:21:04Z

Jimbob: Created page with "Cueball's physics has a mistake on this one (or at least assumes we've managed to heat the atmosphere of Titan to Earth's temperature). The temperature of Titan is roughly 1/..."

2013-06-08T05:44:16Z

Created page with "Cueball's physics has a mistake on this one (or at least assumes we've managed to heat the atmosphere of Titan to Earth's temperature). The temperature of Titan is roughly 1/..."

New page

Cueball's physics has a mistake on this one (or at least assumes we've managed to heat the atmosphere of Titan to Earth's temperature). The temperature of Titan is roughly 1/3 the temperature of Earth on an absolute scale. Starting with the Ideal Gas Law, PV = NkT (k is Boltzmann's constant, N is # of molecules, P is pressure, V is volume, T is temperature), its easy to define the density of a gas, ρ as:

ρ = m/V = (m P)/(N k T) = P (m/N) / (k T)

Titan's atmosphere is 98.4% molecular nitrogen (N2) and on Earth only 78.1% molecular nitrogen (by volume), but for simplicity we'll assume 100% for both. The weight of one molecule of Nitrogen is (m/N) ~ 2 × 14 × 1.67x10-27 (kg/molecule) (there are 28 nucleons per molecule with a mass of about 1.67x10^-27 kg.

The pressure on Titan is PTitan=146.7 kPa, and TTitan = 93.7 K, while on Earth PEarth=101.3 kPa and TEarth = 287 K.

Plugging in numbers, we get ρTitan = 5.3 kg/m3 and ρEarth = 1.2 kg/m3 (note the measured surface density of air on Earth is 1.2 kg/m3 at Earth's mean temperature even without the simplifying assumption of 100% N2).

Hence Titan's atmosphere is 4.4 = (5.3/1.2) times denser than Earth's (or 340% denser); not 50% denser as stated in the comic.

You will get the 50% denser if you assume the same planetary temperature on Titan as on Earth. Titan at 287 K would have a density of ρTitan at 287K ~ 1.73 kg/m3 which is about 50% greater than Earth's.

For the second calculation (panel 2), note {{w|Lift_(force)|lift}} is proportional to the density of air. If your action on Earth creates a lift of L0 and you weigh W0, on Titan you'd have a lift of 4.4 L0 (Cueball calculated 1.5 L0) due to the greater air density. Your weight would only be 0.14 W0, due to Titan's lower surface gravity. If lift balances weight, you would be able to fly on Titan, that is if 4.4 L0 = 0.14 W0. That means to fly on Titan you need a lift on Earth of L0 = 0.03 W0, that is 3% of your Earth weight. Substituting Cueball's Titan density you would get the critical value from the comic: L0 = 0.14 W0/(1.5) = 9% W0.

PS: I largely adapted this [http://forums.xkcd.com/viewtopic.php?f=7&t=43578&hilit=620+wings&start=120#p1726506 my writeup on xkcd forums from 2009 when the comic was made]. [[User:Jimbob|Jimbob]] ([[User talk:Jimbob|talk]]) 05:44, 8 June 2013 (UTC)

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	Okay so maybe I just don't know enough about the physics, but... shouldn't the bricks be dangling? In the illustration, it looks like the rope should have a little slack in it. With nothing keeping it taught, I don't see how it would cancel out any of a person's weight. It also seems like you'd have to account for the friction of the pulleys, which I think would both increase the force required to get off the ground and slow the fall back down. Idk maybe I'm just overthinking this. [[Special:Contributions/172.70.111.34\|172.70.111.34]] 16:18, 5 October 2024 (UTC)		Okay so maybe I just don't know enough about the physics, but... shouldn't the bricks be dangling? In the illustration, it looks like the rope should have a little slack in it. With nothing keeping it taught, I don't see how it would cancel out any of a person's weight. It also seems like you'd have to account for the friction of the pulleys, which I think would both increase the force required to get off the ground and slow the fall back down. Idk maybe I'm just overthinking this. [[Special:Contributions/172.70.111.34\|172.70.111.34]] 16:18, 5 October 2024 (UTC)
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		+	:I agree completely. [[User:Conjuncts\|Conjuncts]] ([[User talk:Conjuncts\|talk]]) 04:03, 24 July 2025 (UTC)
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		+	It occurred to me that you could probably recreate this safely using rock climbing/belay equipment. Clip the flyer into the pulley system; on the other end, set up a harness weighing 91% that person's body weight. Also clip the harness to an active belayer. The belayer's job is to keep the rope only slightly slack, in case of sudden falls. However, you'll need to find a pulley with sufficiently low friction (although that problem is also present in Randall's original setup.) [[User:Conjuncts\|Conjuncts]] ([[User talk:Conjuncts\|talk]]) 04:03, 24 July 2025 (UTC)

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 PS:  I largely adapted this [http://forums.xkcd.com/viewtopic.php?f=7&t=43578&hilit=620+wings&start=120#p1726506 my writeup on xkcd forums from 2009 when the comic was made].  [[User:Jimbob|Jimbob]] ([[User talk:Jimbob|talk]]) 05:44, 8 June 2013 (UTC)
 :That was the whole point of Blackhat's presence. He was there to make sure Rob (AKA Cueball) wasn't hurt.
-:Fortunately, Blackhat couldn't care less about the outcome. So he's got that going for him, which is nice.
+:Fortunately, Blackhat couldn't care less about the outcome. So he's got that going for him, which is nice. [[User:Weatherlawyer| I used Google News BEFORE it was clickbait]] ([[User talk:Weatherlawyer|talk]]) 01:21, 29 January 2015 (UTC)
 Why is this not a thing you can do in amusement parks or places like that?[[Special:Contributions/141.101.104.44|141.101.104.44]] 17:00, 8 September 2016 (UTC)

← Older revision		Revision as of 16:18, 5 October 2024
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	I think that the bridge to which Cueball attached his wings is inspiration for the bridge in [[Click and Drag]].--[[User:Obscure xkcd reference\|Obscure xkcd reference]] ([[User talk:Obscure xkcd reference\|talk]]) 13:47, 13 November 2021 (UTC)		I think that the bridge to which Cueball attached his wings is inspiration for the bridge in [[Click and Drag]].--[[User:Obscure xkcd reference\|Obscure xkcd reference]] ([[User talk:Obscure xkcd reference\|talk]]) 13:47, 13 November 2021 (UTC)
		+
		+	Okay so maybe I just don't know enough about the physics, but... shouldn't the bricks be dangling? In the illustration, it looks like the rope should have a little slack in it. With nothing keeping it taught, I don't see how it would cancel out any of a person's weight. It also seems like you'd have to account for the friction of the pulleys, which I think would both increase the force required to get off the ground and slow the fall back down. Idk maybe I'm just overthinking this. [[Special:Contributions/172.70.111.34\|172.70.111.34]] 16:18, 5 October 2024 (UTC)

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	Why is this not a thing you can do in amusement parks or places like that?[[Special:Contributions/141.101.104.44\|141.101.104.44]] 17:00, 8 September 2016 (UTC)		Why is this not a thing you can do in amusement parks or places like that?[[Special:Contributions/141.101.104.44\|141.101.104.44]] 17:00, 8 September 2016 (UTC)
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		+	I think that the bridge to which Cueball attached his wings is inspiration for the bridge in [[Click and Drag]].--[[User:Obscure xkcd reference\|Obscure xkcd reference]] ([[User talk:Obscure xkcd reference\|talk]]) 13:47, 13 November 2021 (UTC)

← Older revision		Revision as of 17:00, 8 September 2016
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	[[User:Weatherlawyer\| I used Google News BEFORE it was clickbait]] ([[User talk:Weatherlawyer\|talk]]) 01:21, 29 January 2015 (UTC)		[[User:Weatherlawyer\| I used Google News BEFORE it was clickbait]] ([[User talk:Weatherlawyer\|talk]]) 01:21, 29 January 2015 (UTC)
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		+	Why is this not a thing you can do in amusement parks or places like that?[[Special:Contributions/141.101.104.44\|141.101.104.44]] 17:00, 8 September 2016 (UTC)

← Older revision		Revision as of 01:21, 29 January 2015
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	PS: I largely adapted this [http://forums.xkcd.com/viewtopic.php?f=7&t=43578&hilit=620+wings&start=120#p1726506 my writeup on xkcd forums from 2009 when the comic was made]. [[User:Jimbob\|Jimbob]] ([[User talk:Jimbob\|talk]]) 05:44, 8 June 2013 (UTC)		PS: I largely adapted this [http://forums.xkcd.com/viewtopic.php?f=7&t=43578&hilit=620+wings&start=120#p1726506 my writeup on xkcd forums from 2009 when the comic was made]. [[User:Jimbob\|Jimbob]] ([[User talk:Jimbob\|talk]]) 05:44, 8 June 2013 (UTC)
		+	:That was the whole point of Blackhat's presence. He was there to make sure Rob (AKA Cueball) wasn't hurt.
		+	:Fortunately, Blackhat couldn't care less about the outcome. So he's got that going for him, which is nice.
		+
		+	[[User:Weatherlawyer\| I used Google News BEFORE it was clickbait]] ([[User talk:Weatherlawyer\|talk]]) 01:21, 29 January 2015 (UTC)