Up to Units


The magnitude of a measurement is the size of that quantity. Have a look at the following table of physical constants that you may be familiar with. It has been split up to clearly show the difference between the magnitude and the units in each measurement.

Quantity Magnitude Units
Acceleration at the Earth's surface due to gravity9.8m / s^2
Absolute Zero-273.15degrees Celsius
Freezing point of Silver960.8degrees Celsius
Speed of light299792458m / s
Density of Mercury at room temperature13.6g / ml

All of these quantites are measured in units that permit an arbitrary degree of precision. For example. just as we can measure one metre, we can measure 0.1 metres, 0.01 metres and so on, being as accurate as we would wish.

It may seem that this is true of all quantities, but this is not the case. Sometimes we can "measure" something exactly --- as on the next page.

More about magnitudes
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