The measure of all things

Hands-on at the exhibit

• Get involved in seven interactives representing each of the SI base units, including:
• Use a laser interferometer to measure length (SI unit: metre)
• Try a Kibble balance to weigh samples (SI unit: kilogram)

Find out more

Progress in science and engineering is often linked to progress in metrology – the science of measurement. If we cannot measure something then we cannot begin to understand it (science) or improve it (engineering).

Measurement is the quantitative comparison of an unknown quantity with a standard. In the International System of Units – the ‘SI’ – there are seven standard quantities called the ‘base units’: the second, metre, kilogram, ampere, kelvin, candela and mole.

From May 2019 there will be subtle but profound changes in the definitions of four of these base units – the kilogram, ampere, kelvin and mole. For example, we currently define ‘one kilogram’ as the mass of a unique object called the International Prototype of the Kilogram (IPK). Worryingly, studies have shown that the mass of the IPK might be changing, but because of the definition, we have no way of knowing for sure.

On our stand we will demonstrate a ‘Kibble balance’ which uses the new definition of the kilogram to weigh objects against an electromagnetic force rather than a gravitational force. We will also have interactive experiments which illustrate the other SI base units.

Presented by the National Physical Laboratory.