141–150 of 155 posts
Reading about standard kilogram always reminds me 2014 movie "1001 grams" [0]. Not sure how accurate it reflects how the things are actually run there, but was interesting to watch it nevertheless. [0] https://www.imdb.com/title/tt3346824/
Is there a reason why this took so long?
But here is the answer [1]: "The new definition only became possible when instruments were devised to measure the Planck constant with sufficient accuracy based on the IPK definition of the kilogram."
Earlier quoted context omitted.
As a scientist I've gotta say...how are metric prefixes bad? I couldn't do my job without them every day.
As a scientist, use scientific notation off the base units; you eliminate opportunities for confusion. The prefixes don't really add anything. The Sun is 1.5 x 10^11 meters from the Earth. Calling it 1.5 x 10^8 kilometers doesn't help you visualize the distance better, nor calling it 150 gigameters. Now you have three numbers that mean the same thing floating around, and if you accidentally write 1.5 x 10^8 m somewhe…
Earlier quoted context omitted.
As a scientist, use scientific notation off the base units; you eliminate opportunities for confusion. The prefixes don't really add anything. The Sun is 1.5 x 10^11 meters from the Earth. Calling it 1.5 x 10^8 kilometers doesn't help you visualize the distance better, nor calling it 150 gigameters. Now you have three numbers that mean the same thing floating around, and if you accidentally write 1.5 x 10^8 m somewhe…
Personally, I find the prefixes helpful when memorizing approximate values, eg for back-of-the-envelope estimates (proton mass is 1GeV, electron mass is .5MeV, room temperature is 25meV, h_bar c is 197 MeV fm, ...)
Why 1 GeV instead of 160 picojoules?
Earlier quoted context omitted.
You were also never going to test your scale with a weight that is stored in a vault in Paris. So far you would test with a replica of a replica of that weight, in the best case (getting a copy directly from the local standards body). With the new definition in principle anybody can create an object that weighs exactly one kg and sell it to you.
will this increase the probability of adoption of the SI system? I have often had the impression that some nations avoided transitioning to SI out of principle, not wanting to depend on the maintenance and cooperation of another nation?
Earlier quoted context omitted.
> Aside, are the mega and giga prefixes ever used for anything except bits and bytes? Sure, few examples of the top of my head: - Megatons, as in yield of nuclear weapons. Which is a bit odd unit, should be in J, goddammit! - Similarly, energy consumption/production. Commonly used units MWh, GWh, TWh. Again, the proper unit would be J, not Wh. Or Mtoe, for Million tons of oil equivalent.
> Megatons, as in yield of nuclear weapons. Which is a bit odd unit, should be in J, goddammit! That’s what is odd about it? It should be teragrams.
Earlier quoted context omitted.
It's hard to say because the mechanisms for the mass loss are not fully known. In fact, we are just guessing that mass loss actually occurred, and how much did occur. How would we have measured the mass change of the reference kilogram? By definition the reference kilogram was the most stable quantity of mass we could have generated at the time, and the most well protected quantity of mass for the duration of it's se…
Is the concept of a half-life similarly crazy to you?
This article sounds like it got written by a scientist but got butchered through a PR department. It talks about the "Mass of a photon" and weighing them directly, rather than the energy-equivalent mass, which is presumably what they are intending to talk about?
Earlier quoted context omitted.
Is the concept of a half-life similarly crazy to you?
No, and radioactive decay doesn't account for the variances between the reference kilogram and it's sister kilograms we've observed.
>Despite the greatest of precautions, every time the standard kilo was handled — for example, to compare it to another unit that could then be used to calibrate instruments — it would shed some atoms and its mass would be slightly changed. Over its lifetime, that standard kilo is estimated to have lost about 50 micrograms. Why did the standard kilo ever need to be handled? Just store it on a balance and only handle t…
I think they needed to take the replicas from other countries like the US to the master one in Paris for comparison every year. Edit: see this Veritasium episode https://youtu.be/SmSJXC6_qQ8