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Guess I'll km/s (lemmy.dbzer0.com)
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[-] TheIvoryTower@lemmy.world 84 points 4 months ago

In a parallel universe, someone is memeing about how teachers waste our time on useless stuff and never taught us to convert between units.

[-] mkwt@lemmy.world 68 points 4 months ago

This is actually pretty important to being able to solve engineering problems in the real world. Invariably, every little sub industry has its own cursed unit system. And dimensional analysis is great for solving real problems on its own.

And if you get to a high enough physics level, they start setting hbar = c = 1 or G = c = 1, and you never have to worry about it again.

I'm the mean time, it's worthwhile to learn the trick to do this stuff fast-ish.

[-] bitfucker@programming.dev 10 points 4 months ago

I would like to introduce everyone to this video about cursed unit (youtube link warning)

[-] Randelung@lemmy.world 5 points 4 months ago

kWh has an intuitive reason. Watts are so small that you'd always calculate consumption in MJ and whatnot, and seconds are so short that you'd always be expressing time in ks. Using kWh will reduce the numbers to useful ranges and makes cancelling M and k unnecessary.

[-] bitfucker@programming.dev 2 points 4 months ago

Yeah, he elaborated it in his second video about the cursed unit that cursed ≠ useless.

[-] JackbyDev@programming.dev 1 points 4 months ago

I have a soft spot for units like watt hours and foot pounds. I find them very intuitive to explain.

[-] MisterFrog@lemmy.world 6 points 4 months ago

I dislike that my highschool never once gave me the concept that units can simply be treated like constants to be cancelled out.

I used to do the conversions for each variable before putting them in the equation like a fool.

Now I'm slapping all of the conversions alongside the original values/units in a single expression like god intended.

[-] LodeMike@lemmy.today 47 points 4 months ago

Just divide by 3.6

Example:

10 km /h * 1000 m / km = 10,000 m /h

10,000 m/h * 1h/3600s = 10,000/ 3,6000 m/s = 10/3.6 m/s

[-] Psythik@lemmy.world 25 points 4 months ago

Shit like this is why we need metric time.

[-] sparkle@lemm.ee 8 points 4 months ago

don't speak like the french

[-] the_crotch@sh.itjust.works 2 points 4 months ago

Shit like this is why metric needs to be replaced with a base12 system. Base10 is for children who still count on their fingers.

[-] BlueMagma@sh.itjust.works 2 points 4 months ago

Dozenal for the win !!! It will never happen though, but dreaming is allowed

[-] GoodEye8@lemm.ee 1 points 4 months ago

If at could start at blank slate then base 12 would make a better foundation, but base 10 is far too ingrained into every aspect of our life. It's much easier to convert time into base 10 than it would be to convert the world into base 12.

[-] MisterFrog@lemmy.world 2 points 4 months ago

I used to do it this way in highschool, but could never remember if it was divide by or multiply by 3.6

Instead I now do it as you have shown, except it all goes in the same expression.

10 km/h * 1000 m/km * 1h/3600s = 2.778 m/s

No need for the extra steps. Slap it all in the same expression and put it in the calculator (being careful to check that the units cancel as intended)

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[-] SnokenKeekaGuard@lemmy.dbzer0.com 27 points 4 months ago

I'll be pissed if the comments are about metric units

[-] renzev@lemmy.world 73 points 4 months ago
[-] bleistift2@sopuli.xyz 23 points 4 months ago* (last edited 4 months ago)

That’s interesting. Obviously, you’d put a center dot to disambiguate millihertz from meter-hertz, but I can’t recall ever having learned a rule about that. So some combinations of units are inherently ambiguous?

Also: Hz/dpt.

[-] renzev@lemmy.world 17 points 4 months ago* (last edited 4 months ago)

I can't tell which unit is more cursed: millihertz or meter hertz. Surely, anything that could be measured in millihertz is more natural to measure as a period, or as revolutions per minute or something, right?

EDIT: Also, TIL about dpt. Thanks!

A dioptre (British spelling) or diopter (American spelling), symbol dpt, is a unit of measurement with dimension of reciprocal length, equivalent to one reciprocal metre, 1 dpt = 1 m^−1.

[-] Technus@lemmy.zip 7 points 4 months ago

Something that occurs once a hour has a frequency of 277.777... μHz

[-] Technus@lemmy.zip 5 points 4 months ago

You know, I always figured optometry involved like, super complicated math and shit.

Turns out it's just basic arithmetic.

Kinda like programming, in a way.

[-] rockerface@lemm.ee 1 points 4 months ago

Yeah, from my experience ordering glasses, it's mostly about making sure the lenses are aligned with my retinas to focus the light in the right spots. All the numbers are just a way to formalize those measurements so that the lens maker gets it right

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[-] Eheran@lemmy.world 3 points 4 months ago

Speed as meter per hertz is a rather odd case, like with a machine that goes in discrete steps.

In any case, I never use implied multiplication (and others) and always simply put everything where it should be.

[-] Skua@kbin.earth 6 points 4 months ago

Speed is metre hertz rather than metre per hertz. Metres per hertz would measure absement, which is a measure of how far away something is from a start point and for how long. So being twice as far away for half the time would be the same amount of absement.

[-] Eheran@lemmy.world 2 points 4 months ago

Yes, sorry for the little error, my point is that m*Hz it is not generally speed but only in specific cases. Hz is not just "per time" but "something occurring x times per time", like a frequency or revolutions. You can not use it for regular speed, it has to be a periodic event. That is how it is defined:

The hertz is defined as one per second for periodic events.

This is why we have Becquerels to count decay events, which are random and not periodic, but the unit is also 1/s. And for the same reason you can not use m*Bq as speed.

[-] bleistift2@sopuli.xyz 2 points 4 months ago

I never knew that Hertz requires a periodic event. Thanks for that and the Becquerel explanation!

[-] bleistift2@sopuli.xyz 3 points 4 months ago* (last edited 4 months ago)

TIL about dpt

Tell me you don’t [Edit: need] glasses without telling me you don’t need glasses :D

[-] renzev@lemmy.world 2 points 4 months ago

I actually do have glasses, I just never bothered learning about any of the technical details behind my lenses. Optometrist measured my eyes, I chose the cheapest frame the store offered, came back a week later to pick up the glasses and that's about it.

[-] rockerface@lemm.ee 11 points 4 months ago

Thanks, I hate it

[-] perviouslyiner@lemmy.world 8 points 4 months ago* (last edited 4 months ago)

Saw a video using mHz recently and it took way too long to realise the readout was correct and not a typo of MHz ..

[-] 0x0@lemmy.dbzer0.com 8 points 4 months ago* (last edited 4 months ago)

✋ 1 bit

🖖 125 millibytes

[-] JackbyDev@programming.dev 2 points 4 months ago

mbps, milli bits per second

[-] stupidcasey@lemmy.world 7 points 4 months ago
[-] lauha@lemmy.one 2 points 4 months ago
[-] L0rdMathias@sh.itjust.works 19 points 4 months ago

Wait what, jow many kilominutes per hour is one mile per stone?

[-] Entropywins@lemmy.world 9 points 4 months ago

African or European swallow?

[-] lauha@lemmy.one 2 points 4 months ago

Unladen or not?

[-] Lemminary@lemmy.world 14 points 4 months ago* (last edited 4 months ago)

Just multiply by (1000m/1km)(1h/3600s) and cancel out the units, kids

[-] roguetrick@lemmy.world 12 points 4 months ago

Don't ky/s over unit conversions OP. It's not that hard.

[-] orcrist@lemm.ee 9 points 4 months ago

Same order of magnitude, don't bother with the trivial details.

[-] amda@feddit.nl 4 points 4 months ago

Is it really tho? log(3.6) ≈ 0.55 so 1 km/h is really closer to 10m/s than 1m/s

[-] NorthWestWind@lemmy.world 9 points 4 months ago

It isn't even that much of a time waste you just multiply 1000/3600

[-] Plopp@lemmy.world 10 points 4 months ago

But it would take me a couple of hours to figure that out.

[-] deepfriedchril@lemmy.world 14 points 4 months ago

Have you tried converting those hours to seconds?

[-] deadbeef79000@lemmy.nz 3 points 4 months ago
[-] Singh@lemmy.world 2 points 4 months ago

I hate it when they do it !

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this post was submitted on 13 Aug 2024
690 points (97.9% liked)

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