At the end of this lesson, students should be able to:

- Know the meaning of measurement, the metric system, length and time.
- Use current unit of measurement (metric system) in practical situations and express quantities in terms of larger or smaller unit.

Measurement is the assignment of a number to a characteristic of an object or event, which can be compared with other objects or events. The scope and application of a measurement is dependent on the context and discipline . Measurement has been important ever since man settled from his nomadic lifestyle and started using building materials; occupying land and trading with his neighbours. Hundreds of years ago; people in different countries had different system of measurement. They were often based on the human body, example, length of people’s hands, arm, palm and feet. One of the oldest units of length measurement used in the ancient world was the **‘cubit‘** which was the length of the arm from the tip of the finger to the elbow. This could then be subdivided into shorter units like the foot, hand (which at 4 inches is still used today for expressing the height of horses) or finger, or added together to make longer units like the stride. The cubit could vary considerably due to the different sizes of people.

Unit such as these caused confusion because people were **different sizes** and the measures they used **varied**. Consequently, standard units of measurement were developed. As society has become more technologically orientated much higher accuracies of measurement are required in an increasingly diverse set of fields, from micro-electronics to interplanetary ranging.

** Length Measurement Today **

Today length measurement is used in every sphere of life to enable fair trading conditions and to develop new and improved products and processes that enhance our standard of living.

This ranges from the production of microscopic electronic devices with circuit dimensions made to accuracies of some ten thousand millionths of a metre, to millimetre accuracy in distance measurement in construction over many kilometres, But this also extends to everyday life where we rely on accurate length.

__The Metric System (International System of Units: SI)__

The metric system is an internationally agreed system of measurement that was originally based on the **metre** for **length**, **gram** for **mass** and **litre **for** capacity** or **volume**. It is convenient and easy to use because it is a **decimal system**. Smaller units are always ^{1}/_{10}(deci), ^{1}/_{100}(centi) or ^{1}/_{1000} (milli) of the base unit. Larger units are 10 times (deca), 100 times (hector) or 1000 times (kilo) the base unit.

The metric system has been extended to incorporate many more units. The metric system of measurement is now in use in most countries of the world except for the United States. Here is a list of most common metric unit.

Quantity |
Base Unit |
Smaller Unit |
Larger Unit |

Length |
Metre (m) | Centimetre (cm) Millimetre (mm) | Kilometre (km) |

Area |
Square metre (m^{2}) |
Square centimetre (cm^{2}) Square millimetre (mm^{2}) |
Square kilometre (km^{2}) Hectare (ha) |

Volume |
Cubic metre (m^{3}) |
Cubic centimetre (cm^{3}) Cubic millimetre(mm^{3}) |
Cubic kilometre (km^{3}) |

Capacity |
Litre (l) | Milliliter (ml) | Kiloliter (kl) |

Mass |
Gram (g) | Milligram (mg) | Kilogram(kg) Tonne (t) |

Time |
Second (s) | Minute (min) Hour (h) | Day, week, month, year, decade, century, millennium |

Temperature |
Kelvin (K) | Degree Celsius ( ) |

__Example 1__

For each of the following, state what quantity is being measured (length, volume, mass, capacity or time) and the most appropriate unit of measurement.

- A bag of sugar.
- The height of a building.
- The amount of water in a fish tank.
- A spoonful of medicine.
- The distance from Athens to Vienna.

__Solution__

** **Quantity Appropriate unit

- A bag of sugar – mass kilogram
- The height of a building – length kilometer
- The amount of water in a fish tank – capacity litre
- A spoonful of medicine. – volume Millilitre
- The distance from Athens to Vienna – length Kilometre

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