Talk:2073: Kilogram

Explain xkcd: It's 'cause you're dumb.
Revision as of 18:19, 16 November 2018 by Fabian42 (talk | contribs)
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I didn't know that weights and currencies could be converted 1:1, that's cool! Fabian42 (talk) 16:37, 16 November 2018 (UTC)

I wish they had redefined the kilogram a little bit. It would have been neat if 1 kg was exactly the weight of 1 dm^3 (1 litre) of water under one atmosphere of pressure. Right now it's soooo close. It's a good enough estimate for simple maths, but whenever you tell people that a litre of water weighs one kilogram the pedants comes out of the woodworks... Kapten-N (talk) 16:50, 16 November 2018 (UTC)

Up until 1964 a litre (and therefore actually the metre too) used to be defined as the volume that water with mass 1kg takes. But this is not good for exact measurements not only because you need exactly reproducable temperature, pressure (not so problematic, because you can measure them and then calculate the divergence) and gravity (not so easy to measure, because you need an exact mass and exact masses are impossible to keep the same), but also because you need pure water free of any polutions of other stuff (hard and expensive) and even free of tiny amounts of isotopes which are deuterium and tritium (even way more expensive). Because the water that was used then was never close to pure the actual weight of water nowadays is 0.99997kg at 4°C and 1.013bar and I don't know which value for g. There is also another definition which I like, but is hard to measure in real life scenarios: E=mc². A kilogramm should be 1/c² of the mass which anything becomes heavier that you accelerate by the energy of one Joule. -- 17:11, 16 November 2018 (UTC)

But how do you define/measure a Joule then? Fabian42 (talk) 18:19, 16 November 2018 (UTC)

Actually, for the new definition of the kilo using the Kibble balance you need to measure the gravity... 17:34, 16 November 2018 (UTC)

Welp, looks like 1 kg, a.k.a. 1 lb, a.k.a 2.2 lb, is now officially defined to have zero mass. 16:56, 16 November 2018 (UTC)

…or infinite. Fabian42 (talk) 16:59, 16 November 2018 (UTC)
What I understand: the joke is not (only) about 1 (old) kg = 1 (old) lb, but (also) about 1 new kg = 1 old lb... or 1 new lb = 1 old kg :^) Or about a ring of positive characteristic -- 17:08, 16 November 2018 (UTC)