# Tag Archives: Physical Quantities

## Common SI prefixes

* Physical Quantity* is a quantity that

**can be measure**

**d**and it consists of a

**numerical magnitude**(size) and a

**unit**. (e.g. 5m where 5 is the numerical magnitude and m is the unit)

**1) The seven base quantities and their SI units**

Base Quantity |
Name of SI unit |
Symbol for SI unit |

Length | metre | m |

Mass | kilogram | kg |

Time | second | s |

Electric Current | ampere | A |

Thermodynamic temperature | kelvin | K |

Luminous intensity | candela | cd |

Amount of substance | mole | mol |

Out of the seven, for O level Physics, you are required to learn the first 5 *(length, mass, time, current and temperature)*.

**2) Some common derived quantities and units**

Physical Quantity |
How it is derived from base quantities |
Symbol for SI unit |

Area | length x width | m^{2} |

Volume | length x width x height | m^{3} |

Speed | length/time | m/s |

Acceleration | velocity/time | m/s^{2} |

Density | mass/volume | kg/m^{3} |

You can think of base quantities as the smallest building blocks (like Lego bricks). When you combined any base quantities to ‘build’ into something else, they becomes a derived quantity.The derived quantity is ‘derived’ or ‘gotten from’ when 2 or more quantities are combined together.

**3) Prefixes for SI units**Prefixes are used to represent very large or small quantities.For example, instead of writing 1000000 m, it will be more convenient to write 1Mm, which means the same thing!

Factor |
Prefix |
Symbol |

10^{9} |
giga- | G |

10^{6} |
mega- | M |

10^{3} |
kilo- | k |

10^{-1} |
deci- | d |

10^{-2} |
centi- | c |

10^{-3} |
milli- | m |

10^{-6} |
micro- | µ |

10^{-9} |
nano- | n |