Changing Units
It is very important that you are aware that different systems of units exist. Furthermore, you must be able to convert between units. Being able to change between units (for example, converting from millimetres to metres) is a useful skill in Science. The follow...
How to Change Units
It is very important that you are aware that different systems of units exist. Furthermore, you must be able to convert between units. Being able to change between units (for example, converting from millimetres to metres) is a useful skill in Science.
The following conversion diagrams will help you change from one unit to another.
The distance conversion table
If you want to change millimetre to metre, you divide by \(\text{1 000}\) (follow the arrow from \(\text{mm}\) to \(\text{m}\)); or if you want to change kilometre to millimetre, you multiply by \(\text{1 000}\) × \(\text{1 000}\).
The same method can be used to change millilitre to litre or kilolitre. Use the figure below to change volumes:
The volume conversion table
Example:
Question:
Express \(\text{3 800}\) \(\text{mm}\) in metres.
Step 1: Use the conversion table
Use the distance conversion table figure above. Millimetre is on the left and metre in the middle.
Step 2: Decide which direction you are moving
You need to go from \(\text{mm}\) to \(\text{m}\), so you are moving from left to right.
Step 3: Write the answer
\(\text{3 800}\text{ mm} \div \text{1 000} = \text{3,8}\text{ m}\)
Example:
Question:
Convert \(\text{4.56}\) \(\text{kg}\) to \(\text{g}\).
Step 1: Find the two units on the conversion diagram.
Use distance conversion table figure. Kilogram is the same as kilometre and gram is the same as metre.
Step 2: Decide whether you are moving to the left or to the right.
You need to go from \(\text{kg}\) to \(\text{g}\), so it is from right to left.
Step 3: Read from the diagram what you must do and find the answer.
\(\text{4,56}\text{ kg} \times \text{1 000} = \text{4 560}\text{ g}\)
Two Other Useful Conversions
Very often in science you need to convert speed and temperature. The following two rules will help you do this:
Converting speed
When converting \(\text{km·h$^{-1}$}\) to \(\text{m·s$^{-1}$}\) you multiply by \(\text{1 000}\) and divide by \(\text{3 600}\) \(\left(\frac{\text{1 000}\text{ m}}{\text{3 600}\text{ s}}\right)\). For example \(\text{72}\text{ km·h$^{-1}$} \div \text{3.6} = \text{20}\text{ m·s$^{-1}$}\).
When converting \(\text{m·s$^{-1}$}\) to \(\text{km·h$^{-1}$}\), you multiply by \(\text{3 600}\) and divide by \(\text{1 000}\) \(\left(\frac{\text{3 600}\text{ s}}{\text{1 000}\text{ m}}\right)\). For example \(\text{30}\text{ m·s$^{-1}$} \times \text{3.6} = \text{108}\text{ km·h$^{-1}$}\)
Converting temperature
Converting between the Kelvin and Celsius temperature scales is simple. To convert from Celsius to Kelvin add \(\text{273}\). To convert from Kelvin to Celsius subtract \(\text{273}\). Representing the Kelvin temperature by \({T}_{K}\) and the Celcius temperature by \({T}_{℃}\):
\({T}_{K} = {T}_{℃} + 273\)
This lesson is part of:
Skills for Science