Difference between revisions of "Talk:3087: Pascal's Law"

Explain xkcd: It's 'cause you're dumb.
Jump to: navigation, search
(Counterexample: an oversimplified law of physics that leads to a counterfactual conclusion by similar reasoning)
Line 11: Line 11:
  
 
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)
 
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)

Revision as of 01:01, 10 May 2025

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 Randal challenged people to fold a paper too small? This hand-makeable device could get farther on that! 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. - Vaedez (talk) 23:37, 9 May 2025 (UTC)

As someone old enough to remember the 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. 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. 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. 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. Cphoenix (talk) 01:01, 10 May 2025 (UTC)