279

submitted 1 month ago* (last edited 1 month ago) by xkcdbot@lemmy.world to c/xkcd@lemmy.world

79 comments fedilink hide all child comments

Title text:

'This HAZMAT container contains radioactive material with activity of one becquerel.' 'So, like, a single banana slice?'

Transcript:

[Cueball holds a stick while talking with Megan and White Hat.]
Cueball: This stick is one meter long.
Megan: Cool.
White Hat: That's a nice stick.

[Cueball holds a smallish rock.]
Cueball: This rock weighs one pound.
Megan: I'd believe it.
White Hat: Looks like a normal rock.

[Cueball holds a small battery.]
Cueball: This battery is one volt.
Megan: Seems fine.
White Hat: Might need a recharge.

[Cueball holds a capacitor while Megan and White Hat panic.]
Cueball: This capacitor is one farad.
Megan: Aaaaa! Be careful!!
White Hat: Put it down!!

Source: https://xkcd.com/3106/

explainxkcd for #3106

top 50 comments

sorted by: hot top controversial new old

[-] ryannathans@aussie.zone 95 points 1 month ago

Haha that's a good one

Capacitors are usually in the realm of pico to micro farads

A one farad capacitor charged to a respectable voltage would feel like a doomsday device in your hand

[-] HakFoo@lemmy.sdf.org 21 points 1 month ago

You see low voltage ones for things like memory backup on hi-fi gear. I have some 3F/5v capacitors in an old Technics tiner.

[-] SalamenceFury@lemmy.world 10 points 1 month ago

Wait so this is like one mistake away from turning that stickman into a fried stickman?

[-] ricecake@sh.itjust.works 20 points 1 month ago

Depends on the voltage it's charged with, but household current would give it more energy than a shotgun has.

Realistically one would not do that unless you were dealing with something industrial. You would use them otherwise for things like dampening lower voltage systems that need a lot of current.

Closer to the danger level of someone holding two exposed wires plugged into the wall.

[-] bizarroland@fedia.io 5 points 1 month ago

Household current pumped through a full bridge rectifier, that is.

Capacitors don't seem to do very much with AC Other than attenuate it a bit

[-] EpicFailGuy@lemmy.world 5 points 1 month ago

Read in electroboom's voice: FULL BRIDGE RECTIFIER!!!!

[-] AI_toothbrush@lemmy.zip 2 points 1 month ago

Well by attenuate it a bit you mean they pretty much filter ac out if you have the right capacitance and resistance values as capacitors act like low pass filters.

load more comments (5 replies)

[-] ricecake@sh.itjust.works 2 points 1 month ago

Technically correct. The best kind of correct. :)

I basically solved for shotgun, confirmed in was in the ~100V range and disregarded every other consideration for actually doing it.
I'm pretty sure most hand sized capacitors would just pop if you actually tried to put that much in them.

[-] kaidezee@lemmy.ml 2 points 1 month ago* (last edited 1 month ago)

Actually, they act like a short circuit to high-frequency AC, so it is more like "blow up" (in general case).

load more comments (1 replies)

[-] ByteJunk@lemmy.world 2 points 1 month ago

AC units have beefy capacitors, right? Do you know in what range, for comparison?

load more comments (5 replies)

load more comments (2 replies)

[-] kaidezee@lemmy.ml 4 points 1 month ago

That is why I like supercapacitors.

[-] DarkCloud@lemmy.world 3 points 1 month ago

Operation Sundial 2.0, electric boogaloo.

load more comments (3 replies)

[-] ch00f@lemmy.world 37 points 1 month ago

I used to teach AP physics to kids on the weekends. One asked me why Farads were so big. I had to explain that there’s a fixed ratio between Farads, Volts, and Joules. One of them had to be crazy big or crazy small.

See also Coulombs.

Caps are especially scary because they can develop their own charge through static electricity, so large value caps are often shipped with their terminals tied together.

[-] ViatorOmnium@piefed.social 20 points 1 month ago

There's nothing in the SI system that says ratios have to be between base units. Units that involve mass are defined against the kilogram not the gram.

[-] bizarroland@fedia.io 11 points 1 month ago

The kilogram is just a thousand grams, so if they're tied together, they would still be tied together.

[-] bisby@lemmy.world 18 points 1 month ago

Right. 1F = 1C/1V .. they could have just as easily said 1kF = 1C/1V. Many things use kg instead of g. You can tie together things other than the unscaled base units. Then they are still tied together but 1F is a more reasonable amount.

[-] Scipitie@lemmy.dbzer0.com 3 points 1 month ago

You sent me down a freaking rabbit hole, thanks! :)

From what I found is that there is the simple reason that the weird ones are distance, time and weight - the rest I looked into are based on formal non-normalized definitions (including lumen, which surprised me).

My guess is that in depends on where the unit comes from: science or day to day use.

I learned about the Siemens, the Weber and the Gray on the way.

Thanks again!

[-] ViatorOmnium@piefed.social 4 points 1 month ago* (last edited 1 month ago)

They were all done by scientists or engineers.

The meter was defined based on what they calculated as 1 millionth of the length of Paris' meridian.

The second was 1/86400 of a day, which makes sense with the angle/circle nomenclature on the clock.

The gram was initially set to be the mass of 1cm³ of water at 4°C - which is why 1l of water ≈ 1kg.

load more comments (3 replies)

load more comments (1 replies)

[-] _Cid_@lemmy.world 29 points 1 month ago

"This magnet has one tesla"

[-] Treczoks@lemmy.world 7 points 1 month ago

That stucks ;-)

[-] kaidezee@lemmy.ml 4 points 1 month ago* (last edited 1 month ago)

It is not that much though. You could easily make an electromagnet with magnetic flux density of multiple tesla in it's core.

load more comments (1 replies)

[-] Treczoks@lemmy.world 22 points 1 month ago

Only criticism is the use of non-metric weight units when everything else is SI-based.

[-] captain_aggravated@sh.itjust.works 2 points 1 month ago

The joke wouldn't have worked as well.

A gram is actually a pretty small unit of weight, and the joke relies on the base units. It's actually a weird little abberation in the metric system that the "base" unit is considered the kilo gram. so a 1 gram rock would be a little pebble, strangely small.

[-] palordrolap@fedia.io 2 points 1 month ago

Wikipedia currently says:

the international avoirdupois pound, [...] is legally* defined as exactly 0.45359237 kilograms

So, technically, a pound is a metric weight, only a niche one whose use may or may not be permitted by local regulations.

Similar is true* of the inch, which is defined as precisely 25.4 millimetres.

* The US, UK and a handful of others collectively signed this into their respective laws in 1959. You might think we don't use the pound in the UK any more but it still shows up often in informal situations. Ditto inches and feet.

load more comments (4 replies)

[-] freijon@lemmings.world 18 points 1 month ago

This capacitor will cost around one Bitcoin

[-] sxan@midwest.social 2 points 1 month ago

We use it to ignite the tokamak.

[-] Deebster@infosec.pub 15 points 1 month ago

Ah, Randall is alive! I kept thinking my bot had broken as it's so rare for him to miss an upload.

[-] LodeMike@lemmy.today 12 points 1 month ago

However, 1 farad is really goddamn big.

Lol, explainXKCD

[-] Hamartiogonic@sopuli.xyz 12 points 1 month ago

But why pick one pound? The are so many fun units to choose from, only some of which are conveniently sized. How about a stick 1 mile long, or a rock that weights 1 grain?

[-] Simplicity@lemmy.world 21 points 1 month ago

A rock that weighs one stone (14 lbs).

[-] modeler@lemmy.world 7 points 1 month ago

Or a barleycorn that's one barleycorn long? Or a really large foot that's a foot long. Or a chain that's a chain long?

load more comments (2 replies)

[-] SteveTech@programming.dev 9 points 1 month ago

Guys you're not gonna believe this:

50F Super capacitor

[-] Kratzkopf@discuss.tchncs.de 2 points 4 weeks ago

Yes, I do not believe it. It must be a misprint, right?

[-] SteveTech@programming.dev 3 points 4 weeks ago* (last edited 4 weeks ago)

No it's real! I can't verify the exact rating since it OL's my meter, but with some circuitry it can power my Pi for a few minutes. I got them from element14, so it's unlikely to be a fake product.

load more comments (1 replies)

[-] magnetosphere@fedia.io 5 points 1 month ago

I’d be the clueless guy in the room. “I’m not familiar with that unit of measurement.”

[-] pelya@lemmy.world 6 points 1 month ago

A capacitor of 1 farad at standard American 120 volts has the energy between 7.62×54 and .50 BMG, and will discharge just as violently.

[-] spizzat2@lemmy.zip 10 points 1 month ago* (last edited 1 month ago)

Great. Now I get to be the "I’m not familiar with that unit of measurement." guy.

7.62x54

3,291 J (2,427 ft⋅lbf) to 3,400 J (2,508 ft⋅lbf)

.50 BMG

The .50 BMG round can produce between 10,000 and 15,000 foot-pounds force (14,000 and 20,000 J), depending on its powder and bullet type, as well as the weapon it is fired from

[-] Quazatron@lemmy.world 13 points 1 month ago

foot-pounds

Oh, you Americans and your silly made-up units.

[-] Ragnor@feddit.dk 4 points 1 month ago

All units are made up.

I totally agree that imperial units are silly, though. Base 10 is the way things should be.

load more comments (1 replies)

load more comments (2 replies)

[-] udon@lemmy.world 3 points 1 month ago

🚲

[-] Zoomboingding@lemmy.world 3 points 1 month ago

Their names are Cueball, Megan, and White Hat?

[-] captain_aggravated@sh.itjust.works 3 points 1 month ago

It is my understanding that XKCD's "characters" are somewhere between an actual character and an archetype. It isn't clear...and kind of doesn't matter, if Black Hat is the same guy in every comic or if he's a different devious schemer in each. Randall hasn't bothered to name any of them so the community has given them unofficial nicknames.

load more comments (1 replies)

load more comments

this post was submitted on 25 Jun 2025

279 points (98.3% liked)

xkcd

12304 readers

135 users here now

A community for a webcomic of romance, sarcasm, math, and language.

founded 2 years ago

MODERATORS

koraro@lemmy.world