Definition:Metric System/Mass
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Definition
Various metric units of mass which have specific names are as follows:
Milligram
- $1$ milligram is defined as $= \dfrac 1 {1 \, 000}$ of a gram.
Gram
The gram is the CGS base unit of mass.
It is defined as the mass of a cubic centimetre water at the temperature of melting ice.
\(\ds \) | \(\) | \(\ds 1\) | gram | |||||||||||
\(\ds \) | \(=\) | \(\ds 10^{-3}\) | kilogram |
Kilogram
The kilogram is the SI base unit of mass.
It is defined as follows:
- $1$ kilogram is the quantity of mass that would make the fixed numerical value of the Planck constant $h$ to be $6 \cdotp 62607015 \times 10^{-34}$ when expressed in the unit Joule seconds.
The Joule second is equal to $1 \, \mathrm {kg} \, \mathrm m^2 \, \mathrm s^{−1}$, where the metre and the second are defined in terms of:
- the speed of light $c$
- the time of transition between the two hyperfine levels of the ground state of the caesium $133$ atom at rest at $0 \, \mathrm K$.
\(\ds \) | \(\) | \(\ds 1\) | kilogram | |||||||||||
\(\ds \) | \(=\) | \(\ds 1000\) | grams | |||||||||||
\(\ds \) | \(\approx\) | \(\ds 2 \cdotp 20462\) | pounds avoirdupois |
Tonne
- $1$ tonne is defined as $= 1000$ kilograms.
\(\ds \) | \(\) | \(\ds 1\) | tonne | |||||||||||
\(\ds \) | \(=\) | \(\ds 1000\) | kilogram | |||||||||||
\(\ds \) | \(=\) | \(\ds 2204 \cdotp 62\) | pounds avoirdupois | |||||||||||
\(\ds \) | \(\approx\) | \(\ds 0 \cdotp 9842\) | tons |