## The Metric System

 Over the years people have used many different systems for measuring things such as length, volume, speed, etc. In many countries the metric system is used. The metric system was developed in France in the late 18th century. Some countries do not use metric units. For example in the United Kingdom, distances on road signs are given in miles, where a mile is about 1.6 kilometres. In the United States of America, weights are measured in pounds instead of kilograms. Under the metric system there are basic units for length, mass, capacity and time. Many other units are combinations of these.e.g. Areas can be measured using m2, volumes can use m3 and speed can be measured in m/s.

Because many measurements are too large or too small to be conveniently expressed in these basic units, other units are used with prefixes such as kilo- or milli-.

### Things to Measure

Length
Lengths such as distances between towns, perimeters of shapes and lengths of object are measured using the basic unit of the metre.

 Length Units Comparison Basic Unit metre (m) 1 metre = 100 cm1 metre = 1000 mm Other units millimetre (mm) 10 mm = 1 cm1000 mm = 1 m centimetre (cm) 10 cm = 1 dm100 cm = 1 m kilometre (km) 1 km = 1000 m1 km = 100 000 cm

Mass
Mass or as it is commonly known, weight, is a measure of how heavy an object is and is measured using the basic unit of the gram.

 Mass Units Comparison Basic Unit gram (g) 1 gram = 1000 mg Other units milligram (mg) 1000 mg = 1 g kilogram (km) 1 kg = 1000 g

Capacity
Capacity or volume is a measure of how much a container can hold or how much space an object takes up and is measured using the basic unit of the litre.

 Capacity Units Comparison Basic Unit litre (L) 1 litre = 1000 mL Other units millilitre (mL) 1000 mL = 1 L
 TimeTime is measured using the basic unit of the second. There are no other special metric units for time and the other units used include minutes, hours, days etc. Temperature
The basic unit of temperature is the degree centigrade (or degree Celsius).

The freezing point of water is 0°C and the boiling point of water is 100°C.

Converting Between Units
For measurements too big or too small for the basic units, the following prefixes can be used:

 Multiple of 10 Exponent Prefix Symbol Smaller than the basic unit × 1⁄1000 × 10-3 milli- m × 1⁄100 × 10-2 centi- c × 1⁄10 × 10-1 deci- d The basic unit × 10 × 10 deca- D or da × 100 × 102 hecto- h Bigger than the basic unit × 1000 × 103 kilo- k

There are other prefixes for even bigger and smaller units, such as mega − , which is a million times bigger than the basic unit and micro -, which is a million times smaller than the basic unit.

Examples

 What? How? Why? Example Change metres into centimetres Multiply by 100 1 m = 100 cm Change 3.4 m into cm. 3.4 m = 3.4 × 100 cm= 340 cm Change millilitres into litres Divide by 1000 1000 mL = 1 L Change 500 mL into L 500 mL = 500 ÷ 1000 L= 0.5 L Change kilograms into milligrams Multiply by 1 000 000 1 kg = 1 000 000 mg Change 0.6 kg into mg 0.6 kg = 0.6 × 1 000 000 mg= 600 000 mg

### Everyday Use of Units To give an idea of the size of some of the more commonly used units:

 Measurement Unit Examples (approximation) Length 1 metre m1 kilometre km1 centimetre cm The width of a doorThree laps of a running trackThe width of a \$1 coin Mass (weight) 1 gram g1 kilogram kg1 Tonne T A pinch of saltTwo packets of butterA small truck Capacity 1 litre L1 millilitre mL A carton of milk5 mL is a small teaspoonful of liquid