Scientists must cope with lots of different units, and if many formulae are to be used correctly, then quantities must be put into SI units. What approach should we take to change the units that have been given into the units we need to use to find a solution to a problem? For example, a sample of material may be said to have a density of 2.7 g cm–3, but what is that in kgm–3, kgdm–3, or mg ml –1?
If you are going to use the gas equation PV = nRT then all quantities must be in SI units. Taking another example, we have been told that a force exerted is in newtons (N), but the area over which it acts is in millimetres squared (mm2). How do we confidently change that area into m2, which we need to do to know the value of the pressure in pascals (1 Pa = 1Nm–2)? Some people find these things straight-forward, but how can we be sure that we have not made a mistake when doing the conversion? Here is a simple method of changing units and checking that we have not made a mistake.
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