Scientific data is collected, presented and then analysed. It is important to evaluate the quality of data before drawing a conclusion.

Scientists use Standard International (SI) units. The table shows some common units.

Quantity | Unit name | Unit symbol |
---|---|---|

Length | metre | m |

Mass | kilogram | kg |

Time | second | s |

Temperature | degree Celsius | °C |

Pressure | pascal | Pa |

Energy | joule | J |

Scientists measure a wide range of quantities, some very large and some very small. Measurements for different orders of magnitude have specific prefixes:

Prefix name | Prefix symbol | Factor | Power |
---|---|---|---|

tera | T | 1,000,000,000,000 | × 10^{12} |

giga | G | 1,000,000,000 | ×10^{9} |

mega | M | 1,000,000 | ×10^{6} |

kilo | k | 1,000 | × 10^{3} |

centi | c | 0.01 | ×10^{-2} |

milli | m | 0.001 | ×10^{-3} |

micro | μ | 0.000,001 | ×10^{-6} |

nano | n | 0.000,000,001 | × 10^{-9} |

Chemists also use the prefix deci (d, power 10^{-1}) when discussing volume:

- 1 dm = 10 cm
^{3} - 1 dm
^{3}= 10 × 10 × 10 = 1,000 cm^{3}

To convert between a unit with difference prefixes, multiplication or division of the right factor of ten (10, 100, 1000) is used.

Always do a sense check when multiplying or dividing and ask "is the answer expected to be larger or smaller?"

- Question
Convert 5 cm into mm.

1 cm = 10 mm so the conversion is × 10

5 × 10 = 50 mm

This is what would be expected because millimetres are smaller than centimetres.

Time is dealt with differently if it is recorded in minutes, as this is not an SI unit:

- 1 minute = 60 s

- Question
Convert 2 minutes 40 s into seconds.

2 minutes = 2 × 60 = 120 s

2 minutes 40 s = 120 + 40

= 160 s