explain xkcd - User contributions [en]

3087: Pascal's Law

2025-05-10T02:01:33Z

172.71.178.143: /* Explanation */

{{comic
| number = 3087
| date = May 9, 2025
| title = Pascal's Law
| image = pascals_law_2x.png
| imagesize = 400x459px
| noexpand = true
| titletext = Reductio ad absurdum fails when reality is absurd.
}}

==Explanation==
{{incomplete|This page was created by PASCAL’S HYDRAULIC PRESS. Don't remove this notice too soon.}}

{{w|Pascal's law}} is a principle of fluid mechanics that states that when a change in pressure occurs in confined incompressible fluid, it is transmitted throughout the fluid and the same change occurs everywhere. It was discovered by mathematician {{w|Blaise Pascal}} in 1653 and published a decade later. This is the principle underlying {{w|hydraulics}}, and the diagram shows a hydraulic lift that allows a heavy weight to be lifted (on the right) by pressing on a small amount of fluid in the vessel on the left.

''{{w|Ruina montium}}'' ("wrecking of mountains" in Latin) was an ancient Roman mining technique in which small tunnels would be dug into the side of a mountain. When the tunnels were filled with high-pressure water, the rock adjacent to the tunnels would fracture, making it significantly easier to remove.

''{{w|Reductio ad absurdum}}'' ("reduction to absurdity" in Latin) is a form of argument in which something is assumed to be true and then this is shown to lead on to absurdity or falsehood, such that the original premise can't be true after all. In mathematics it's called {{w|proof by contradiction}}. For the title text, however, it is pointed out that some truly real things already ''are'' 'absurd', so it would be wrong to rely upon this method to {{tvtropes|AluminumChristmasTrees|conclude that they don't occur}}.

==Transcript==
{{incomplete transcript|Don't remove this notice too soon.}}

[At the left, a teacher is holding a pointer, pointing at a picture on the screen.]

[The picture shows a hydraulic lift, with a small fluid vessel on the left connected to a tube at the bottom, which connects to a large vessel on the right. On top of the large vessel is a weight labeled 1000 and a Cueball. The fluid in the large vessel is labeled with an upward arrow. Megan's hand is over the small vessel, with a downward arrow indicating that she's pressing on it.]

[Cueball, Hairbun, and Blondie are sitting at school desks going right to left.]

Cueball: No, that can't be right.

Cueball: If hydrostatic pressure worked that way, then you could use it to make machines that exert near-infinite force.

Cueball: And ancient people could have demolished entire mountains just by drilling small tunnels and filling them with water.

[Caption below comic:]

When I first learned about Pascal's law, I tried to disprove it by showing that it would lead to absurd consequences, but it turns out hydraulic presses and ''ruina montium'' are both real things.

{{comic discussion}}<noinclude>

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Jill]]
[[Category:Comics featuring Blondie]]

Talk:3086: Globe Safety

2025-05-08T06:49:49Z

172.71.178.143:

Hello! First time i got to a comic first --[[Special:Contributions/172.69.176.76|172.69.176.76]] 06:17, 8 May 2025 (UTC){{unsigned ip|104.23.175.202}}
:Well [[269: TCM|first of all]] remember to sign your comments :-). But congratz... --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 05:42, 8 May 2025 (UTC)
::Sorry.
::I now realize that that was an extremely trollish thing to do. ٠ـ٠

I believe he indicates that a globe is made by making a copy of the Earth, and then compressing it until it fits on a desktop. Hence having the same mass and thus the same Schwarzschild radius as Earth. I have changed the explanation a bit because of this observation.--[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 05:42, 8 May 2025 (UTC)

Gotta wonder what kind of a desk could support a desktop globe that weighs as much as the Earth
--[[User:StumbleRunner|StumbleRunner]]

Radius. {{strikethrough|Is there a typo in the comic where 7/10" should be 7/20", i.e., 0.35" as later written? Or would a 7/10" Earth collapse into a black hole nonetheless?}}[[Special:Contributions/172.71.154.129|172.71.154.129]] 06:40, 8 May 2025 (UTC)
:Nope… the Schwarzchild radius is 0.35", which is indeed 7/20", but the measurement shown on the globe is the diameter, not the radius, so 7/10" is correct. [[Special:Contributions/172.71.178.143|172.71.178.143]] 06:49, 8 May 2025 (UTC)

3067: SawStart

2025-03-24T22:09:07Z

172.71.178.143: /* Explanation */

{{comic
| number = 3067
| date = March 24, 2025
| title = SawStart
| image = sawstart.png
| imagesize = 290x313px
| noexpand = true
| titletext = Unfortunately, SawStart is one-use-only. Once started, the blade cannot be stopped, and must be replaced with a fresh blade while the running one is carefully disposed of.
}}

==Explanation==
{{incomplete|Created by a SawBOT - - Language is too informal and convoluted.}}
{{w|SawStop}} is an American {{w|table saw}} manufacturer whose product is designed to increase safety. Table saws can be highly dangerous if not used properly, because they feature a rapidly spinning {{w|circular saw}} protruding from the surface. If any part of someone's body comes into contact with the blade while it's spinning, it can cause severe injury or death. SawStop products feature an automatic brake, designed to detect when flesh comes into contact with the blade. According to manufacturer claims, the brake (an aluminum block) will stop the blade within 5 milliseconds of detecting contact, followed by the blade retracting into the table. This is intended to prevent major injuries in the event of contact.

Black Hat here takes the notion of a product designed to increase safety, and changes the design to do the opposite, making it much more dangerous. Like the SawStop design, his product ostensibly detects contact with skin and reacts within milliseconds, but rather than stopping the blade, his product uses an explosive charge to ''start'' a stationary blade. It's unknown whether the blade would be faster than normal, and actually make it more dangerous (ordinary speeds of a table saw are more than capable of destroying living tissue), but setting off an explosive charge while in contact with such a blade is probably not a particularly good idea. It is not wise, in general, to touch even a normal stopped blade (without being absolutely certain that the power cannot be turned on, or even just through the stationary sharpness), but in this case it specifically is designed to make one that theoretically could be touched run up to significantly damaging speeds the moment it is. There is no benefit to such a system, and it exists solely to be malicious (which is likely why it's "less popular").

The title text refers to the fact that the braking feature on the SawStop is single use. Because of the very fast response time, both the braking cartridge and the saw blade will be badly damaged in the process, and both will need to be replaced (this being considered preferable to the kinds of permanent injuries that can result from a spinning blade). The SawStart is also single use, but in its case, it somehow makes the blade impossible to stop, violating the second law of thermodynamics and probably several other laws.{{Citation needed}} Hence, the SawStart blade must also be replaced, but this apparently has to be done while the blade is spinning. To attempt to remove a spinning blade is incredibly dangerous, and this simply adds to the unnecessary harm this product could do.

A similar thing was done in [[2876: Range Safety]], but that time was with a rocket.

==Transcript==
:[A table with a table saw stands behind Black Hat who gestures to the table while facing Megan and Cueball. There is a label on the side of the table, a logo of a circular saw blade, with the first part of a word inside the blade:]
:SawStart
:Black Hat: When the saw detects contact with skin, an explosive charge starts the blade spinning at full speed within a few milliseconds.

:[Caption below the panel:]
:SawStop's less-popular competitor

{{comic discussion}}

[[Category:Comics featuring Black Hat]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Cueball]]