# 8 Astrophysics – Part A “Units”

### Aims…

8.1 use the following units: kilogram (kg), metre (m), metre/second (m/s),
metre/ second2 (m/s2), newton (N), second (s), newton/kilogram (N/kg)

### General Ideas…

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:

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.

 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-1ms-2 g or a Momentum kgms-1 p

### Resources…

Use this powerpoint for a quick review…  8 Astrophysics Part A Units

https://www.youtu.be/DTv_eI9Hlro