A LEGO Watt Balance: An apparatus to determine a mass based on the new SI

TL;DR

This paper describes the design and construction of a LEGO-based watt balance that demonstrates the measurement of mass and the realization of the kilogram in the new SI system, suitable for educational purposes.

Contribution

It introduces a novel, accessible LEGO watt balance for educational demonstration of the kilogram realization based on the Planck constant.

Findings

Achieved 1% relative uncertainty in measuring a gram mass.

Demonstrated the principle of the watt balance using a LEGO model.

Showcased an educational tool for understanding SI base units.

Abstract

A global effort to redefine our International System of Units (SI) is underway and the change to the new system is expected to occur in 2018. Within the newly redefined SI, the present base units will still exist but be derived from fixed numerical values of seven reference constants. More specifically, the unit of mass, the kilogram, will be realized through a fixed value of the Planck constant $h$. For instance, a watt balance can be used to realize the kilogram unit of mass within a few parts in $10^8$. Such a balance has been designed and constructed at the National Institute of Standards and Technology. For educational outreach and to demonstrate the principle, we have constructed a LEGO tabletop watt balance capable of measuring a gram size mass to 1 % relative uncertainty. This article presents the design, construction, and performance of the LEGO watt balance and its ability to determine $h$