Devised by French
scientists in the late 18th
century to replace the chaotic collection of units then in use. The goal of this effort was to produce a system that did not rely on a miscellany of separate standards, and to use the decimal system rather than fractions.
To obtain a standard of length a
quadrant of the earth (one-fourth of a
circumference) was surveyed (actually only in part) along the
meridian that passes through
Paris. This distance was divided into ten million parts to become the meter (spelled metre in some countries - including France (mètre)). The definition of the meter has become more and more
precise through the years since. Currently the meter is the distance light travels in a
vacuum in 1/299 792 458 second.
The
nautical mile used in modern
navigation, in relation to which boat speeds and wind
velocities are measured (one
knot is one nautical-mile-per-hour), is defined as one minute of
latitude. A degree of latitude therefore is 60 nautical miles. The quadrant of the earth measured by the
French, being 90 degrees, measures 90x60 or 5400 nautical miles. Therefore: 5400 nautical miles exactly equal 10-million meters, or 10 000 kilometers.
The
units most commonly used from the metric system are listed below:
- m - meter/metre, for length.
- kg - kilogram, for mass/weight.
- t - ton, 1000 kg.
- s - second, for time.
- °C - degrees Celsius, for temperature. Water freezes at 0°C and boils at 100°C.
- m2 square metre, for area.
- ha - hectare, 10,000 m2.
- l - liter/litre, for volume. 1 l of water at 4°C weighs 1 kg.
- m3 - cubic metre, 1,000 litres.
- m/s - metres per second - for wind speeds.
- km/h - kilometres per hour - 3.6 metres per second - for velocities of
cars/planes/bicycles/joggers
- N - newton, for force (the force of a 1 kg weight lifted form the ground (on Earth) is about 9.82 N .. BUGGER!!)
- kPa - kilopascal, for pressure.
- J - joule, for energy. J=N*m.
- W - watt, for power. 1 W = 1 J/s.
See also -
English units / Metric conversion factors