From the yoctogram to the grave

Nanotechnologists in Spain have used the world’s most sensitive scales to measure the smallest unit of mass — the yoctogram — according to New Scientist. One yoctogram (yg), at just one septillionth of a gram, is a hundred times less than the previous smallest mass ever measured (a 10th of a zeptogram).

This tiny mass was measured using nanotubes, which vibrate at different frequencies depending on the mass of the particles or molecules on them. The sensor was able to weigh an atom of xenon to the nearest yoctogram, or 10–24 grams, making it the first scale capable of measuring a single proton, which weighs 1.7yg. This could enable the diagnosis of health conditions by identifying the proton-scale differences in molecular mass that are markers of disease.

But how did people weigh stuff before they discovered nanotubes? Before the kilogram was adopted as a standard unit, one could equate a bag of sugar to one grave. The size of a gram was defined in 1795 as “the absolute weight of a volume of pure water equal to a cube of one hundredth of a metre, and at the temperature of the melting ice”. A more practical unit of mass a thousand times larger — the grave — had been in use since 1793.

But by the time a metallic reference standard had been manufactured in 1799 (see “Prospector”, PJ 2011;287:67), the government of the new French Republic decided that the name grave was politically incorrect as it resembled the aristocratic German title of Graf, or count. Hence the kilogram replaced one of the shortest lived units of measurement in 1799.

If you prefer imperial measures, the slug is a unit of mass equivalent to around 15kg. The blob, or slinch, is equal to 12 slugs.

If you have something a little heavier to measure, palaeontologists use elephants to measure dinosaur mass (one elephant is around six tons).

And if you are working on a galactic scale, you might want to use the solar mass, which is around 2x1030kg. In case you were wondering, the Milky Way weighs in at around 6x1011 solar mass.

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