Mar 2017

Types of SI Units

March 9, 2017

The international system of units [or Système international d’unités in the original French that is the acronym SI units] has simplified and revolutionized the world of science, enabling scientists of all sorts of backgrounds to be able to clearly and effectively communicate. Here’s a little bit more about the SI units that aren’t covered in physics tuition in Singapore.

SI Units are systems of measurement, aren’t they?

Yes, they are. The concept of a measurement is very simple- you are going to take your unknown quantity of a physical or chemical product, and compare it to a system of regularized reference quantities appropriate for the substance or concept being measured.
It gets clumsy and awkward to talk like this, however, and that is where units come into the picture. They are the reference framework for different substances/quantities. Obviously, as scientific principles evolved in different locations worldwide, people invented their own names for these ‘units’ of different substances and energies.
Take a moment to imagine how confusing that could be, especially as we have moved into an era where scientific research is collaborative across countries and continents. If each involved party isn’t working with the same reference system, how can you know that results are consistent? You can’t. Many of these original unit systems had nothing to do with each other, and in fact were rather arbitrary- perhaps based on a certain length of someone’s palm or the distance between two arbitrary points on the body.

So how did SI units evolve?

It was during the French revolution that first saw the rise of a standardized system- the metric system we still use today- in 1875, it was until 1960 at the eleventh Conférence Générale des Poids et Mesures (CGPM) for the SI system we know today to begin appearing. Now scientists could truly talk each other’s languages.

What are the SI Units?

SI units consist of the 7 base units, each selected to represent a predictable, repeatable sample:

  • The ampere (A)
  • The kelvin (K)
  • The candela (cd)
  • The second (s)
  • The mole (mol)
  • The meter (m)
  • The kilogram (kg)

And then the units derived from them. These are complementary and are expressed in terms of the base units [even if the names appear different]. These can then have prefixes [we are most familiar with centi and milli, although the prefix system covers 10-24 times the units].
The derived units are worthy of their own article, but these cover units of electricity and magnetism [units such as the joule and volt], mass [newton and pascal], length [radian and metre], luminous intensity [lux and lumen], Energy flow [watt], time and temperature/radiation.
It is critically important during your JC physics tuition that you have a good base understanding of the SI units for each equation, and why this system of units simplified and made possible modern scientific research. Remember the system is not stagnant, adjustments and new units can be added as scientific progress is made.

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