The kilogram is a strange unit, yes? An SI mass unit referenced to a certain arbitrary physical object [the International Prototype Kilogram, funnily also known as Le Grand K] whose mass is actually fluctuating? Yes.
I read though, today, that if and when the coulomb is absolutely defined at [6.241 509 629 152 65 ×10 to the power of 18] elementary charges [an elementary charge is the charge carried by a single proton, although the absolute value of the charge of a single electron is the same], which has been proposed, the kilogram will become an SI derived unit, a much more respectable status.
If the coulomb had an exact numerical value based on a natural unit such as the elementary charge, this value could be combined with the definition of an ampere:
"the constant current which will produce an attractive force of [2×10 to the power of –7] newton per metre of length between two straight, parallel conductors of infinite length and negligible circular cross section placed one metre apart in a vacuum.", which must also be equal to a charge of one coulomb per second flowing past a fixed point.
Since force in newtons must equal [mass in kg times acceleration in metres per second squared]
one kilogram could be defined as the mass which will accelerate [2 x 10 to the power of -7] metres per second squared if subjected to the [2 x 10 to the power of -7] newton force which defines the ampere and therefore the coulomb.
Tell me whether or not this was remotely intellible. I want to get better at it.
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1 comment:
I only understood that through what parallels I could draw to chemistry. That is not, however, a reflection on your understanding of the subject, just my inability to comprehend physics. It seems quite logical to me.
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