Talk:3087: Pascal's Law

2025-05-12T23:35:32Z

162.158.62.109:

I remember learning about this and thinking it was intuitive, but I didn't really think of these consequences. Maybe everybody is making powerful lifting machines for lifting cars and houses with your bare hands, rather than explaining the article, that there isn't one yet. Pascal's law basically says that if you make one end of a container of fluid X times larger, then any force exerted on the small end is multiplied by X on the large end, so you can make it near-infinite by making the small end very small. But you'll need a little more machinery added (like a gear system) if you want the distance actually moved to be higher. Actually I think that might undo the gains in force entirely. That might be how it happens, it might swap distance for force so the same work is performed.

Hey, remember that comic where Randall challenged people to fold a paper too small? This hand-makeable device could get farther on that!
[[Special:Contributions/172.70.111.110|172.70.111.110]] 21:46, 9 May 2025 (UTC)
: yes, that's how it works; the total work is constant and the hydraulic system is converting a small force over a long distance to a large force over a small distance. if you additionally want the force to be over a larger distance, you need to put more energy into the system or else you could push this machine with its own output and get free energy from nothing. really though hydraulics are just smoother, backlashless, equivalents to a gear train in the first place so you generally wouldnt need to use both. - [[User:Vaedez|Vaedez]] ([[User talk:Vaedez|talk]]) 23:37, 9 May 2025 (UTC)
:: Small tube needs to be X times as long to get same displacement. Good for linear force rather than torque. Fluid's own pressure can be the force if tube is long enough. [[Special:Contributions/172.68.55.33|172.68.55.33]] 11:41, 10 May 2025 (UTC)

As someone old enough to remember the [https://en.m.wikipedia.org/wiki/Slashdot_effect slashdot effect], I wonder if XKCD comics generate a similar effect on search engines. Though I doubt they would buckle under the weight these days. [[Special:Contributions/172.69.60.148|172.69.60.148]] 22:00, 9 May 2025 (UTC)

To whoever wrote the initial transcript, remember that we don't include the title text. [[User:Barmar|Barmar]] ([[User talk:Barmar|talk]]) 22:06, 9 May 2025 (UTC)

I have to wonder whether he has the same disbelief of, say, levers... which allow one to move the Earth. [[User:Jordan Brown|Jordan Brown]] ([[User talk:Jordan Brown|talk]]) 23:34, 9 May 2025 (UTC)

Although some laws of physics are absolute and lead to extreme consequences, others are taught in a simplified form that can lead to wrong conclusions. For example, "Light and heavy objects fall at the same rate" can be used to prove that objects fall at the same rate on the Earth and the Moon - which is far from correct. If the Moon were somehow dropped onto the Earth, it would fall at a certain rate. The Earth dropped on the Moon would necessarily fall at the same rate. So if the Moon falling on the Earth fell at the same rate as a bowling ball, then the bowling ball would have to fall at the same rate on the Moon. When I read Heinlein's _The Rolling Stones_ as a pre-teen, where he describes things falling slower on the Moon, I applied this reasoning and concluded that Heinlein must have made a mistake. The solution to this paradox is that something as big as the Moon will not only accelerate toward the Earth, it will significantly accelerate the Earth toward it, so the Moon does not actually fall at the same rate as a bowling ball. [[User:Cphoenix|Cphoenix]] ([[User talk:Cphoenix|talk]]) 01:01, 10 May 2025 (UTC)
: I think if you stand at the shared center of mass of the Earth and Moon, that then you see the Moon falling toward the Earth according to its constant field of gravitational acceleration, as well as the Earth falling toward the Moon according to its constant field of acceleration. It was indeed confusing for me to realize this, involving visit to pages such as https://en.wikipedia.org/wiki/Gravitational_acceleration . F=Gm1m2/r^2 so if m1 is taken out you get a constant F=m1 a2 and vice versa. But I think the page says this only holds if the masses are far enough from each other to be treatable as points. [[Special:Contributions/172.68.55.47|172.68.55.47]] 11:57, 10 May 2025 (UTC)

Besides, isn't it better to just ''believe'' in Pascal's Law if it offers a reward of near-infinite force?
[[User:StapleFreeBatteries|StapleFreeBatteries]] ([[User talk:StapleFreeBatteries|talk]]) 04:58, 10 May 2025 (UTC)
:I'll wager that you're pleased with that reference... ;) (Whether or not you actually were!) [[Special:Contributions/172.71.26.43|172.71.26.43]] 15:58, 10 May 2025 (UTC)

Could this be referencing or inspired by this recent paper talking about the use of hydraulics to build pyramids? https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0306690 [[Special:Contributions/172.68.234.169|172.68.234.169]] 08:52, 10 May 2025 (UTC)

It could be noted that simple machines can multiply forces more or less arbitrarily, but only up to what the machine itself can withstand. Many "why didn't the ancients do that?" can be answered with "bronze kind of sucks". [[Special:Contributions/172.69.246.149|172.69.246.149]] 14:19, 10 May 2025 (UTC)
:Right. Archimedes's "Give me a lever long enough..." assumes that the lever is made of a material that won't buckle or snap under the weight of the Earth. If there were a material like that it would make building long bridges much simpler. [[User:Barmar|Barmar]] ([[User talk:Barmar|talk]]) 16:58, 10 May 2025 (UTC)
:It is also quite difficult to efficiently contain a fluid under pressure in a moving system. All considerations of innovation-stiffling aside, the same problem hindered the use of the Stirling engine untill very recently. Force applied to a rigid mediom is much easier to predict / monitor (a solid either holds or doesn't, but it doesnt leak -not in a way that would have been hindering the use in everyday life by "the ancients" anyway). To a certain extent it is also the reason why most common bikes still use cable brakes : sure it't less efficient but it's much cheaper and you can repair them in no time with common garden-shed-grade equipment.{{unsigned ip|172.71.232.101|22:07, 11 May 2025 (UTC)}}
:I think the hydraulic press is different from the lever in that the material only needs to withstand the pressure of the fluid, not the total force exerted by the press. The force is spread over the large area of the pressing end, such that the entire surface area holds the same pressure as the smaller end at every point. [[Special:Contributions/162.158.63.90|162.158.63.90]] 23:33, 12 May 2025 (UTC)

;Donald Knuth?
Is there a name for the teacher character (a cueball with tufts of hair on the sides of his head)? [[User:Barmar|Barmar]] ([[User talk:Barmar|talk]]) 16:58, 10 May 2025 (UTC)

:The teacher appears to be Donald Knuth, though not sure why Randall has used him.--[[User:Darth Vader|Darth Vader]] ([[User talk:Darth Vader|talk]]) 09:14, 11 May 2025 (UTC)

::We should add the comic to [[:Category:Comics featuring Donald Knuth]] then. --[[User:FaviFake|FaviFake]] ([[User talk:FaviFake|talk]]) 10:09, 11 May 2025 (UTC)

----

Here's a reference that claims that water hammer, rather than just depth pressure, was the major effect used in ''ruina montium'': https://blog.ferrovial.com/en/2022/08/ruina-montium-use-water-for-digging-romans/ -- [[User:Dtgriscom|Dtgriscom]] ([[User talk:Dtgriscom|talk]]) 00:04, 11 May 2025 (UTC)

A few years back I posted a question on Stack Exchange (https://history.stackexchange.com/questions/60189/which-mountain-collapsed-in-france-in-1820-21) about a report, in a 19th-century biblical commentary, of a mountain collapsing due to just this kind of thing - fluid pressure building up. First thought when I saw the reference to ''ruina montium'' in the comic was that maybe that's it - but no. So, just curious: anyone have any thoughts on what event is being referred to in that commentary? (The one suggestion that someone made there, about a glacier advancing, doesn't seem to fit.) Thanks! [[Special:Contributions/172.71.23.87|172.71.23.87]] 03:38, 11 May 2025 (UTC)
:No idea, but I gotta say, that font or scan is unreadable. Some words are decipherable like הר גבוה and ובמקומו but damn, about half of it is just splotches. No idea how you could read that. --[[User:NeatNit|NeatNit]] ([[User talk:NeatNit|talk]]) 05:12, 11 May 2025 (UTC)
::I hear. There's a transcript of it (though without the diagram) at https://he.wikisource.org/wiki/%D7%9E%D7%9C%D7%91%D7%99%22%D7%9D_%D7%A2%D7%9C_%D7%90%D7%99%D7%95%D7%91_%D7%9E%D7%91_%D7%99%D7%93. [[Special:Contributions/172.70.175.208|172.70.175.208]] 18:50, 11 May 2025 (UTC)

Should there be a goofs section here, because the white board is drawn with perspective, but the picture on it is not. It will look odd, like the whole contraption is tilted, to the students[[User:Drkaii|Drkaii]] ([[User talk:Drkaii|talk]]) 09:10, 11 May 2025 (UTC)

I don't know how to write it, but someone should probably write the actual *point* of the comic: Randall coming up with ridiculous scenarios to disprove the theory, only to be informed that those scenarios actually happened.{{unsigned ip|172.69.70.145|23:57, 11 May 2025 (UTC)}}

Also don't forget that there was a Mythbusters episode to this effect (well, in reverse and with air, but same principle), it's possible to lift a car with a single household vacuum-cleaner just by splitting the hose into a few dozen rather large suction cups. More surface area = more force for the same pressure.{{unsigned ip|162.158.3.106|07:06, 12 May 2025 (UTC)}}

I'm sure there must be a name for the belief of absurdity (or counterintuitiveness) due to ignorance or failure/refusal to understand the entirety of a circumstance, or overgeneralization of known outcomes that only partially match the circumstance in question. If there is, that should probably be mentioned in the explanation. Does anyone here know what that might be? [[User:SammyChips|SammyChips]] ([[User talk:SammyChips|talk]]) 16:17, 12 May 2025 (UTC)
:Maybe not entirely congruous with what you describe, but the "{{w|Argument from incredulity}}" is still somewhat similar. [[Special:Contributions/141.101.99.94|141.101.99.94]] 22:13, 12 May 2025 (UTC)
:Do you mean forming incorrect inferences by leaving out some of the facts? [[Special:Contributions/162.158.62.109|162.158.62.109]] 23:35, 12 May 2025 (UTC)

2434: Vaccine Guidance

2021-03-09T19:01:00Z

162.158.62.109: /* Explanation */

{{comic
| number = 2434
| date = March 8, 2021
| title = Vaccine Guidance
| image = vaccine_guidance.png
| titletext = I can't wait until I'm fully vaccinated and can safely send chat messages in all caps again.
}}

==Explanation==

On the day this comic was published, the CDC released [https://www.cdc.gov/coronavirus/2019-ncov/vaccines/fully-vaccinated-guidance.html new guidelines] relating to COVID-19, lifting many of the existing restrictions for people who have been fully vaccinated for two weeks. [[Megan]], speaking as a CDC announcer, is introducing these new guidelines over video conference. However, the other participants in the conference quickly start asking about [[2238: Flu Shot|actions that have little or nothing to do with the vaccine, some of which would be dangerous whether COVID-19 was a risk or not.]]

Blondie asks whether it would be okay to visit neighbors and drink milk directly from the carton. In most Western cultures, drinking directly from a container that could be shared with others (such as a milk carton) is considered unsafe, due to the risk of diseases being transmitted, and generally gross, as saliva and other biological material is passed that way. To drink directly from your own milk carton is considered crass, to do so with someone else's carton would be seen as unacceptable. While these risks are arguably worse during the pandemic, it was unacceptable before the pandemic and will presumably be so afterward.

Science Girl asks whether it would be okay to ride a bike down the stairs of a family member's house, which has a severe risk of injury{{Citation needed}} (and could damage the wheels of the bicycle, although modern bicycle wheels are [https://www.youtube.com/watch?v=VfjjiHGuHoc surprisingly resilient]).

[[White Hat]] follows up asking whether he can get a horse, and whether it would help for both him and the horse to wear masks. In typical White Hat fashion this has basically no relation to anything else that was said (perhaps he was [[1086: Eyelash Wish Log|promised a pony]] when he got vaccinated). The CDC still recommends masks for humans when in public; however, face masks are not generally made for horses. Instead of answering, Megan hangs up.

In the title text, Randall mentions that when he is fully vaccinated, he will be able to text people in ALL CAPS. This is generally used to indicate that the typer is shouting, which can spread Covid-19 aerosol particles and cause infection when done in person. However, when texting, there is no risk of spreading diseases via the computer, so this is an unnecessary precaution{{Citation needed}} (although it could be a good idea to get in the habit of not responding to others angrily, both to be polite and to not spread respiratory diseases by shouting when meeting in person).

==Transcript==

:[Megan is seen at the bottom of the panel with the CDC-logo slightly above her and to the left]
:Megan: Our new guidance: Fully vaccinated people can gather privately with no masks or distancing, and can visit with unvaccinated low-risk people in one household. Any questions?
:[Blondie, Hairy and Megan are seen at the bottom of the panel in separate rectangular panels with Blondie and Hairy's panels being more squarish and smaller then Megan's. Blondie is directly above Hairy and both are to the right of Megan]
:Blondie: If my neighbors and I are all vaccinated, can I visit them unmasked and drink milk straight from the jug in there frigde?
:Megan: I...You can visit, yes.
:Blondie: And the jug thing?
:Megan: ...Next question?
:[Hairbun and Megan are at the bottom of the panel in rectangular boxes, similar to in a video call.]
:Hairbun: I'm fully vaccinated. Can I ride my bike in my sister-in-law's house?
:Megan: In her <i>house?</i>
:Hairbun: Like, down the stairs.
:Megan: I guess? You should at least wear a helmet.
:Hairbun: Even if she's not high-risk?
:Megan: Any <i>other</i> questions?
:[Megan is off-panel; White Hat is in a rectangular box at the bottom of the panel.]
:White Hat: I'm two weeks past my second dose.
:White Hat: Can I get a horse?
:Megan: Thank you all for coming.
:White Hat: What if I wear a mask?
:White Hat: What if the horse does?
:SFX: Meeting ended by host.

{{comic discussion}}
[[Category:COVID-19]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Science Girl]]
[[Category:Comics featuring White Hat]]

explain xkcd - User contributions [en]

Talk:3087: Pascal's Law

2434: Vaccine Guidance