= Сообщение: 12227 из 12492 ===================================== ENET.SYSOP = От : Michiel van der Vlist 2:280/5555 28 May 23 14:10:30 Кому : Vincent Coen 28 May 23 14:10:30 Тема : Metric vs archaic (was: A computer I can recommend) FGHI : area://ENET.SYSOP?msgid=2:280/5555+64734b2a На : area://ENET.SYSOP?msgid=2:250/1@fidonet+646e3d7b = Кодировка сообщения определена как: CP850 ================================== ============================================================================== Hello Vincent,
On Wednesday May 24 2023 17:15, you wrote to me:
>> Ah Gallons... US vs Imperial. Even more more confusion. :(
VC> You have to remember that the majority of a/c both commercial and VC> G.A. are American made, yes there are the odd manufacturer outside but VC> if memory serves they specify fuel burn if not by weight then by VC> gallons (US) as the piston engines are made by only two primary VC> companies and both as yes, you guessed it, American.
The world of measuring volumes is bigger that that of measuring fule for piston engines used in aircraft...
VC> Now for turbine they do not use gallons or litres but by weight and VC> that changes on temperature i.e.,
The physicist here says it is the other way around. It is the volume that changes with temperature while the wight, or mora accuarately the mass does not change with temperature.
>> A "UK litre"? Is that diffenet from an ISO litre?
VC> The is only the one standard for Litre - same as kilometer and this VC> is based on the length of arc around the world from east to west or VC> the opposite.
Th meter, and hence the kilometer WAS based on the size of the earth, but no more.
VC> Don't know where a litre came from or don't remember.
It is directly derived from the meter. 1 liter is 1/1000 kubic meter.
Nowadays the basic units of the SI system are no longer based on astronimical fenomena or man made objects. They are all defined in terms of the natural constants. Accurate to the quantum level en reproducible in any lab on earth. Any lab in the unviverse actuallly. *1)
It starts with the second. Used to be 1/86400 part of e mean solar day. Now it is:
> The second, symbol s, is the SI unit of time. It is defined by taking > the fixed numerical value of the caesium frequency, deltaVCs, the > unperturbed ground-state hyperfine transition frequency of the caesium > 133 atom, to be 9 192 631 770 when expressed in the unit Hz, which is > equal to s-1.
The meter once was 1/1 0.000.000 of the length of the Paris meridian from Pole to Equater. Later is was the lenght of a platinum irridium bar saved in Sévres near Paris. Now it is:
> 1/299.792.458 of the distance that light travels in a vacuum in one > second.
The kg. Originally the mass of a liter of water at 4 centigrade. Later the mass of a platiunum irridium cylinder saved in Sevres near Paris. The present definition is derived by defining the Planck constsant as exactly 6,626 070 15 × 10-34 kg·m2·s-1.
This may become a bit technical but now the kg is defined in terms of the mass equivalent of a set of fotons with a certain frequency.
*1) Or so we think. Ity is based on the assumption that the natural constants sucg als the speed of light and the Planck constant are the same all over the universe (space & time). There are good reasons for this assumption but nature has surprised us before...
