The metric system is a decimal-based system of measurement that has become the standard for most of the world. It is based on seven base units and uses prefixes to denote multiples and submultiples of these units[1]. Here’s a comprehensive overview of the metric system:
Base Units
The International System of Units (SI), the current standard for the metric system, is built on seven base units:
- Metre (m) for length
- Kilogram (kg) for mass
- Second (s) for time
- Ampere (A) for electric current
- Kelvin (K) for temperature
- Mole (mol) for amount of substance
- Candela (cd) for luminous intensity
All other units in the metric system are derived from these base units[1].
Prefixes
The metric system uses standardized prefixes to denote multiples and submultiples of units. Here’s a table of common prefixes:
| Prefix | Symbol | Factor | Power |
|---|---|---|---|
| tera | T | 1,000,000,000,000 | 10^12 |
| giga | G | 1,000,000,000 | 10^9 |
| mega | M | 1,000,000 | 10^6 |
| kilo | k | 1,000 | 10^3 |
| hecto | h | 100 | 10^2 |
| deca | da | 10 | 10^1 |
| (none) | (none) | 1 | 10^0 |
| deci | d | 0.1 | 10^-1 |
| centi | c | 0.01 | 10^-2 |
| milli | m | 0.001 | 10^-3 |
| micro | μ | 0.000001 | 10^-6 |
| nano | n | 0.000000001 | 10^-9 |
| pico | p | 0.000000000001 | 10^-12 |
These prefixes allow for easy conversion between units and provide a consistent way to express very large or very small quantities[1].
Derived Units
Derived units are formed by combining base units. Some examples include:
- Hertz (Hz) for frequency: 1/s
- Newton (N) for force: kgâ‹…m/s^2
- Joule (J) for energy: Nâ‹…m
- Watt (W) for power: J/s
- Volt (V) for electric potential: W/A
- Tesla (T) for magnetic flux density: kgâ‹…s^-2â‹…A^-1
Historical Development
The metric system originated during the French Revolution in the late 18th century. Key milestones include:
- 1790: Charles Maurice de Talleyrand-Périgord proposed a new system based on natural units to the French National Assembly
- 1799: The new system was launched in France
- 19th century: The system evolved and gained international adoption
- 1960: The International System of Units (SI) was established
Advantages of the Metric System
- Decimal-based, making calculations and conversions easier
- Coherent system where derived units are logically related to base units
- Universally adopted by the scientific community
- Used by most countries worldwide, facilitating international trade and communication
Realisation of Units
Modern definitions of base units are based on fundamental physical constants. For example:
- The metre is defined as the distance light travels in 1/299,792,458 of a second
- The kilogram is defined in terms of the Planck constant
This approach ensures greater precision and stability in measurements[1].
Everyday Applications
The metric system is used in various aspects of daily life:
- Weather reports (temperature in °C, rainfall in mm)
- Food packaging (mass in g or kg, volume in ml or l)
- Road signs in most countries (distances in km, speed limits in km/h)
- Scientific and medical measurements
Metric System Variants
Several variants of the metric system have existed:
- CGS (centimetre-gram-second) system
- MKS (metre-kilogram-second) system
- MKSA (metre-kilogram-second-ampere) system
- Gaussian system
The SI system has largely superseded these variants in most applications[1].
Global Adoption
The metric system has been adopted as the official system of weights and measures by nearly all nations worldwide. Notable exceptions include the United States, which still primarily uses the US customary system for everyday measurements[1].
In conclusion, the metric system provides a coherent, decimal-based framework for measurement that has become the global standard. Its logical structure, ease of use, and universal applicability have made it an essential tool in science, commerce, and everyday life.
[glossary_wikipedia]
The metric system is a decimal-based system of measurement. The current international standard for the metric system is the International System of Units (Système international d'unités or SI), in which all units can be expressed in terms of seven base units: the metre (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol), and candela (cd). These can be made into larger or smaller units with the use of metric prefixes.
SI derived units are named combinations – such as the hertz (cycles per second), newton (kg⋅m/s2), and tesla (1 kg⋅s−2⋅A−1) – or a shifted scale, in the case of degrees Celsius. Certain units have been officially accepted for use with the SI. Some of these are decimalised, like the litre and electronvolt, and are considered "metric". Others, like the astronomical unit are not. Ancient non-metric but SI-accepted multiples of time (minute and hour) and angle (degree, arcminute, and arcsecond) are sexagesimal (base 60).
The "metric system" has been formulated in a number of different ways over the centuries. The SI system originally derived its terminology from the metre, kilogram, second system of units, though the definitions of the fundamental SI units have been changed to depend only on constants of nature. Other metric system variants include the centimetre–gram–second system of units, the metre–tonne–second system of units, and the gravitational metric system. Each of these has some unique named units (in addition to unaffiliated metric units) and some are still in use in certain fields.