Definition of kilogram set to change


Cat whisperer
Nov 23, 2011
Sitting in the sun (between the rain storms)
This is something I've been aware of in passing for some time - a move to change the way fundamental units are defined. Back in the dim and distant past, one of my lecturers was Prof Ian Mills, one of the people behind this change.

Definition of kilogram set to change

This is only dimly related, but two days ago I learned from my German chums that a German pound (ie unit of weight) is 500grams, as opposed to the imperial 454g we recognise in Blighty. Ain't life grand?
I thought the kilogram was defined as the mass of a litre of water, and because the litre is 10cm cubed, was therefore derived from the metre, which was defined (incorrectly, as it turned out) as a proportion of the Earth's circumference.

If that is the case, then why the existence of a particular block of metal that now needs to be updated?

And if it isn't the case, how wow of a coincidence is it that it also equals the mass of a litre of water?

ETA: bored of waiting two minutes for a response from you lot, I googled it.

Kilogram - Wikipedia
So does this mean that the value of a kilogram will depend on the strength of gravity wherever you're measuring it? Or is everyone going to have to know the exact gravitational acceleration wherever they make the measurement, and apply a fudge factor to compensate for variations?
I thought the kilogram was defined as the mass of a litre of water
Current definition: The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram.

2019 definition: The kilogram, symbol kg, is the SI unit of mass. It is defined by taking the fixed numerical value of the Planck constant h to be 6.62607015×(10 to the minus 34) when expressed in the unit J⋅s, which is equal to kg⋅m2⋅s−1, where the metre and the second are defined in terms of c and ΔνCs.

There's a Wiki article on all the new definitions.
I believe it's going to be the amount of electricity needed to power an electromagnet to pick up a kilo of, I think, platinum?

EDIT: Like they pick-up the kilo as it stands now, and from then on it will be the electrical definition that applies?
So will I gain or lose weight when this happens?
It will be a bonus if I shed a little bit without a diet.
Nature doesn't stand still. There is always movement in nature. Fixing this kilogram is obviously not so easy. Nature doesn't like fixed constants. They have to be defined by mathematical properties, when used in science measurements that can weigh a single atom, etc.

(Best way to lose weight: quit beer, lol. Imo)

EDIT: But then, as Kingsley Amis observed: No pleasure is worth giving up for the sake of two more years in a geriatric home in Weston Super Mare ...
Last edited:

Similar threads