Explaining to different audiences the new definition and experimental realizations of the kilogram

Abstract

Abstract. Different options were discussed before reaching the final agreement on the new definitions of the SI units, effective from 20 May 2019, especially with regard to the kilogram, now defined in terms of the numerical value of the Planck constant ( h ). Replacing the artefact definition of the kilogram with a new one based on the mass of a particle, or the atomic mass constant ( mu ), would have been preferable for ease of understanding, among other reasons. In this paper we discuss some limitations of teaching to different audiences what a kilogram is in the redefined International System of Units (SI), including realizations of the new definition.