Academic journal article Teaching Science

Metric versus Imperial Units of Measurement: Relevance to Science, Agriculture and Our Daily Lives

Academic journal article Teaching Science

Metric versus Imperial Units of Measurement: Relevance to Science, Agriculture and Our Daily Lives

Article excerpt

Despite some decades of metrication in many countries, strong influences from non-metric countries (especially USA and UK) motivate students to understand non-metric units. A series of studies is offered on the nature and equivalence of metric and imperial (US) units of measurement, including historic aspects of the systems and some specific units. Sections may be used in classes from time-to-time as 'bight-sized' segments, or the full story may be used as a whole lesson.


Student motivation

We need to have a common language if we are to communicate. That will be evident to any students who have travelled to countries where they have not understood the language. Likewise, we need a common 'language' of standard units of measurement for coherent dialogue to proceed in trade and science.

Although students now live in a metric environment 'at home', they are exposed to the US and UK environment of imperial units via movies, books, travel and the internet. They are thus motivated to understand the relationships between the metric and imperial systems.

An understanding of units of measurement is essential to all quantitative aspects of science and technology. Ideally, this system of units should be uniform, but the world still struggles internationally with two major systems of weights and measures. Meaningful interactions risk break down if there is no general agreement about what those units are and the size of each unit of measurement, whatever the parameter being described.

The International System of Units (SI System)

During the 1960s, Australia went metric. At about that time and since, many other countries also transferred from imperial to metric (particularly former British colonies), anticipating a world-wide adoption of the SI system of metric units (Le systeme international d'unites). However, the USA has hardly proceeded with genuine adoption, and metrication is proceeding slowly in the UK. For example, British people currently buy petrol in litres and drive in miles. The US still uses imperial units, although some of these US units differ from those (e.g., the gallon) used in the UK.

The SI system of metric units has developed as a result of successive General Conferences on Weights and Measures, starting in 1889 and continuing about four-yearly to the present, with world-wide representation. At the 10th such conference (in 1954), seven base units were adopted: the metre, the kilogram, the second, the ampere, the Kelvin (for temperature), the mole, and the candela (for luminous intensity). All other metric units are derived from these. At the 11 th such conference in 1960, the official symbol 'SI' was allocated for the Systeme International d'Unites as the 'modernised metric system' providing a practical system of units for unifying techniques for measurement used in industry, commerce research and education (reviewed by Lentner, 1981). The 11th conference also confirmed prefixes (pico-, nano-, micro-, mega-, giga-and tera-) to indicate powers of ten as prefixes to the SI units (see further detail below).

Translation still needed from one system to another

Despite the lack of general adoption of the metric system in the USA, its limited use there has also involved spelling changes that further confound the possibility of international standardization. Specifically, the tonne, litre, metre and gramme of the SI Metric System have become the metric ton, the liter, the meter and the gram, respectively, in U.S, spelling and terminology.

The U.S. is 'officially' on the metric system. All U.S. units are defined in terms of SI units. The use of 'Customary U.S. Units' continues to be permitted in trade, but they are not mandated. In many cases, including consumer foods, such as canned foods and packaged baking mixes, there is dual-labelling-in U.S. Customary Units as well as in the metric equivalent. …

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