33 The metric system
Many ancient measurements were loosely based on the human body.
Cubits, hand spans and feet are well known examples. The problem is that they’re not accurate for most people.
Online research
- What exactly is the metric system? Could you explain to a child what is so special about it?
- Where does the metre originally come from (Wikipedia can help with this)?
- If it’s so great, why does the USA still use imperial units ?
- How would you build a measurement system from scratch?
The metric system
The key to the usefulness of the metric system is that it is based on the decimal system, which makes conversion between units particularly convenient. For example 1 kilometre is 1000 m, 1 metre is 100 centimetres and so 1 kilometre is [latex]1000 \times 100 cm = 10,000 cm[/latex]. We will focus on the following:
| Prefix | Symbol | Meaning | Length | Mass | Capacity |
| mega | M | million | Mm | Mg | Ml |
| kilo | k | thousand | km | kg | kl |
| hecto | h | hundred | hm | hg | hl |
| deka | dk | ten | dkm | dkg | dkl |
| Benchmark unit | one | m | g | L | |
| deci | d | tenth | dm | dg | dl |
| centi | c | hundredth | cm | cg | cl |
| milli | m | thousandth | mm | mg | ml |
The prefixes meaning 1000 (kilo-), 100 (hecto-) , 10 (deka-) come from Greek, while 1/1000 (milli-), 1/100 (centi-) and 1/10 (deci-) come from Latin, however there are also prefixes that derive their names from Italian (pico- means a trillionth) and Danish (femto- and atto- are respectively a quadrillionth, quintillionth).
Online research
In the table on this page, we’ve shown units in the metric system for length, mass and capacity. There are many other things that we could measure that also work using the metric system. Spend up to 15 minutes finding out a little bit more about one of the units of measurements below that is unfamiliar to you.
- Newtons
- Joules
- Watts
- Hertz
How small are microchips?
 |
We sometimes hear about measurements in nanometres.
A nanometre is a billionth of a metre (I.e., 1 000 000 000 nm = 1 m). Small microchips in computers can be small as 10 nm, and the average is 14nm. What would these measurements be in millimetres? |
