All physical quantities, such as distance, speed, energy, among others, are related to some system of units, such as the International System of Units (SI), the MKS system (meter – kilogram – second), the Imperial system (used in countries such as the United Kingdom), among others.
Most physical quantities have a wide range of values - from very small to very high. We can cite as an example the mass physical greatness :
Electron mass : 9,109.10 -31 kg
Mass of the Sun : 1,989.10 30 kg
With this example, it is possible to notice that some quantities can easily differ by up to 60 decimal places.
SI prefix table
To simplify the writing and reading of values with so many digits, the International System of Units allows us to use several prefixes. Observe a table with the SI prefixes below:
| Name | Symbol | Base Power 10 | Decimal |
| Yotta | Y | 10 24 | 1000000000000000000000000 |
| Zetta | Z | 10 21 | 1000000000000000000000 |
| Exa | AND | 10 18 | 1000000000000000000 |
| Peta | P | 10 15 | 1000000000000000 |
| Will have | T | 10 12 | 1000000000000 |
| Giga | G | 10 9 | 1000000000 |
| Mega | M | 10 6 | 1000000 |
| Kilo | k | 10 3 | 1000 |
| Hecto | H | 10 2 | 100 |
| Deca | gives | 10 1 | 10 |
| none | none | 10 0 | 1 |
| Deci | d | 10 -1 | 0.1 |
| Centi | ç | 10 -2 | 0.01 |
| Mili | m | 10 -3 | 0.001 |
| Micro | μ | 10 -6
Don’t stop now … There’s more after the publicity;) |
0.00001 |
| Nano | n | 10 -9 | 0.000000001 |
| Peak | P | 10 -12 | 0.000000000001 |
| Femto | f | 10 -15 | 0.000000000000001 |
| Atto | The | 10 -18 | 0.000000000000000001 |
| Zepto | z | 10 -21 | 0.000000000000000000001 |
| Yocto | y | 10 -24 | 0.000000000000000000000001 |
SI unit prefixes
It is possible to notice that the comma shifts to the right in the decimal place for numbers greater than 1 and shifts to the left in numbers less than 1.
Examples of using unit prefixes
See some examples of using unit prefixes:
- 02 m= 2.10 -2 m 2 = c m – two centi meters
- 003 g= 3.10 -3 g = 3 m g – three milli grams
- 400 s= 4.10 2 seconds = 4 H s – four hectares in seconds
- 1000000 Hz= 1.10 6 Hertz = 1 G Hz – one gig hertz
- 1000 m= 1.10 3 m = 1 k m – 1 kilometer meter
- 1000000000 W= 1.10 9 W = 1 G W – 1 gig watts
- 000009 g= 9.10 -6 g = 9 μ g – nine micro grams
Conversion of fixed quantities – Examples
To carry out the conversion of some preset physical quantity , we must write it in scientific notation (referring to the table of prefixes) and then move the comma until we reach the power of 10 for the prefix to be converted.
We must always remember that:
- Movingthe comma to the left, we add one to the exponent of the power of 10;
- Movingthe comma to the right, we subtract one from the exponent of the power of 10.
Conversion examples
- Convert 1 cm to m m:
1.0 x 10 -2 m = 10 x 10 -3 m → 1 cm = 10 mm
→ c = 10 -2 and m = 10 -3
As we go from -2 to -3, we move the comma to the right.
- Convert 3 km to d m:
→ k = 10 3 and d = 10 1
As we go from 3 to 1, we move the comma to the right twice .
3.0 x 10 3 m = 300.0 x 10 1 dam → 3 km = 300 dam
