# Derived Unit

### SI unit

1. The International System of Units (abbreviated SI from the French language name Système International d’Unités) is the modern form of the metric system.
2. It is the world’s most widely used system of units, both in everyday commerce and in science.

### Derived Unit

1. The derived unit is a combination of base units through multiplying and/or dividing them.
2. For instance,  Speed is defined as the rate of distance change, and can be written in the mathematic form

Example:
Find the derived unit of density.

### Conversion of the Unit of Speed, Density and Pressure

1. When doing the conversion of unit such as speed and density, we are advised to write the quantity in the fraction form.
2. For example, to convert 5km/h to m/s, we write 5km/h as
3. After that, we convert the km to m and h (hour) to s (second)

Example

Complete the following unit conversion of speed.

1. 90 kmh-1 = __________ ms-1
2. 8.12 ms-1 = __________ kmh-1

Example
Complete the following unit conversion of density and pressure.

1. 760 kgm-3 = __________ gcm-3
2. 5.1 gcm-3 = __________ kgm-3
3. 3600 Nm-2 = __________ Ncm-2
4. 3.16×10-5 Ncm-2= __________ Nm-2