The SI Unit Change
Based on the 2018 Physics IPSGX Keynote Sharing by Dr Thomas Liew at Eunoia JC.
How do we measure? Most of us take measurements for granted, glancing at the clock to determine how much time we have left or stepping on the scale to figure if our new exercise regime is working. However, how have we determined what “how much” is, or means?
The working and progress of society is dependent on a uniform system of weights and measures, as such a system facilitates the exchanges of goods, regulates our daily affairs and much more. In order for such a system to work, the system of measures needs to be
Invariant
Stable in the long term
Able to be realised anywhere and anytime
The previous set of SI units was formalised in 1875 and partially based on physical quantities. This had its disadvantages. For example, the kilogram took reference from a single standard weight “the big K”. Replicas of this weight were taken and sent to various countries. However, the big K has been losing mass, while its replicas have been gaining and losing mass at different rates.
In comparison, the Kelvin was calibrated off the triple point of water– a state where vapour, water, and ice can coexist, and this experiment could be carried out by anyone with the correct expertise at anywhere, given the right equipment.
The variation of standards such as the big K led scientists to launch into a review of the SI unit, and the most drastic revision to the SI unit will be voted on in 16 November 2018. It is is expected to be approved and the new definitions will come into force on 20 May 2019.
The newest sets of SI units which will be based on defining constants such as speed of light c, Planck’s constant h, electron charge e and other SI units. Furthermore, all of these SI units will be realisable using experiments– meaning that calibration can be done, given the correct set of apparatus, and expertise– without the need from an external physical object. This may not affect us in daily life by much.
However, it will help make researchers and industries everywhere more certain of their measurements, bringing humanity one more step closer to a truly universal measurement system.
Some ideas about bringing this into your Physics classrooms include:
Asking your students to consider how measurement accuracy affects their daily life.
Have them do a mini-project/presentation on older units of measurement such as the English Imperial system or the Chinese and Japanese units of time.
You can also watch out for the CPDD-NMC video collaboration on SLS which will be coming up within the next year!
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