While the emphasis on SI units in introductory physics textbooks has mercifully eliminated the use of English units, the exclusion of other systems of units is not necessary. For years physicists have simplified calculations by doing things like setting [h-bar] = c = 1. We could not imagine putting 4[pi][epsilon][subscript 0] into the formulas for…

The current use of two sets of units in the UK continues to be a source of muddle and confusion. Young people are taught metric (SI) units in school but, in the outside world, still have to contend with units such as inches, feet, pounds, stones and miles. Specialist teachers and practitioners of the sciences are not blameless. This paper…

Important changes were recently made to the International System of Units. The readers involved in chemistry and physics, either teachers or advanced students, should be aware of the new definitions of the kilogram, the mole, and more generally of the changes in International System of Units (SI, "Système International") recently…

On November 16, 2018, at the 26th meeting of the General Conference on Weights and Measures (CGPM), a resolution was adopted that introduced historical changes into the International System of Units (SI). This decision, effective from May 20, 2019, established that the SI units of measurement will be defined by means of a set of seven fixed…

The United States is one of only three countries in the world that remain uncommitted to the metric system. Perhaps to policymakers the decision to hang on to miles, pounds, and gallons is one of tradition. However, as a physics teacher I have seen firsthand how growing up with U.S. Customary Units (commonly called by the pseudonym "British…

The non-SI unit sverdrup, named to honor Norwegian oceanographer and meteorologist Harald Ulrik Sverdrup (1888-1957), is adopted for quantifying large-scale volume transport by oceanographers, meteorologists, and atmospheric physicists. The sverdrup is used to appraise the volumetric rate of evaporation, precipitation, runoff, transport of ocean…

Plans are under way to redefine the International System of Units (SI) around 2018. The new SI specifies the values of certain physical constants to define units. This article explains the new SI in order to provide a resource for high school teachers as well as for advanced students already familiar with the pre-2018 SI.

This study aims to determine the challenges faced by mathematics teacher-candidates on unit conversion and dimensional analysis. The research was conducted using content analysis method of qualitative research methods. The study group consists of 66 people, 50 females and 16 males, elected through appropriate sampling method, studying at state…

The definition of the kilogram, the unit of mass in the International System of Units (SI), has not changed in more than 125 years. The kilogram is still defined by the mass of a Pt-Ir cylinder conserved at the International Bureau of Weights and Measures. Science and technology have progressed to the point where it is likely the kilogram will be…

Since much of SI is based on physics and mathematics, physics teachers have the background to teach SI. We present this review and summary in a series of SI notes in order to help teachers answer many questions about the SI that often are, or should be, asked (for example, in workshops for teachers). SI should not be considered a jargon to set…

The proposed revision of SI units would embed Planck's constant into the definition of the kilogram, as a fixed constant of nature. Traditionally, Planck's constant is not readily interpreted as the size of something physical, and it is generally only encountered by students in the mathematics of quantum physics. Richard Feynman's…

Before discussing more details of SI, we will summarize the essentials in a few tables that can serve as ready references. If a unit isn't listed in Tables I-IV, it is not part of SI or specifically allowed for use with SI. The units and symbols that are sufficient for most everyday applications are given in bold.

The International System of Units (SI) is a coherent system based originally on measurements of properties of material objects. In more recent times, the adopted definitions depend on setting values of universal constants wherever possible. The last remaining human-made material object on which a standard is based is a platinum-iridium kilogram…

As all physicists know, all units are arbitrary. The numbering system is anthropocentric; for example, the Celsius scale of temperature has 100 degrees between the boiling point of water at STP and the freezing point of water. The number 100 is chosen because human beings have 10 fingers. The best units might be based on physical constants, for…

The covariant formulation of Maxwell's equations can be expressed in a form independent of the usual systems of units by introducing the constants alpha, beta and gamma into these equations. Maxwell's equations involving these constants are then specialized to the most commonly used systems of units: Gaussian, SI and Heaviside-Lorentz by giving…