### Aims…

1.1 use the following units: kilogram (kg), metre (m), metre/second (m/s),metre/second^{2} (m/s^{2}), newton (N), second (s) and newton/kilogram (N/kg)

**1.2P use the following units: newton metre (Nm), kilogram metre/second****(kg m/s) (Triple)**

**General Ideas…**

A **physical quantity **is something that can be measured. For any measurement, the unit being used must be stated to give an understanding of the scale of the measurement.

For example, distance can be measured in **kilometres** or in miles. They are similar, but not the same and it is important to identify which was used for the measurement, to know how far the distance actually is.

**Système Internationale d’Unités**

The units that scientists use all over the world are standardised in the Système Internationale d’Unités – **SI units**. It is important to remember these **six fundamental **(or ‘base’) units of measurement:

**metre**(m) – unit of length**kilograms**(kg) – unit of mass**second**(s) – unit of time**ampere**(A) – unit of electrical current**kelvin**(K) – unit of temperature**mole**(mol) – unit of the amount of substance

There are many quantities scientists **measure** that come from the base units. These derived units are very useful to quote as **measurements**, but they are not **fundamental** as they come from **fundamental** units.

For example, **frequency** is the number of times something happens per unit of time.

This is a useful quantity, but it is a **division** into the **time unit**.

The standard unit for **frequency** is considering the number **‘per second**‘, which is called **‘hertz**, Hz’, but this comes from the **fundamental** unit **‘second**‘.

Name | Unit | Abbreviation |

Frequency | hertz | Hz |

Force | newton | N |

Energy | joule | J |

Power | watt | W |

Pressure | pascal | Pa |

Electric charge | coulomb | C |

Work Done or Work | Nm or J | W |

Gravity or acceleration | Nkg^{-1}ms^{-2} | g or a |

Momentum | kgms^{-1} | p |

### Resources….

Use this PowerPoint for a quick review… 1 Force and Motion Part A Units