Search This Blog


Saturday, June 1, 2019

redefining the kilogramme !!

How much do you buy ~ and how is that quantified ? – in Kilogrammes ??

One is bound to ask – ‘what’s in a name ?’ ~ a rose by anyother name would smell as sweet !  .. .. before you proceed further – have you heard of ‘Saint-cloud’ ?-  it is a commune in the western suburbs of Paris, France. It is known to be one of the wealthiest towns in France. The town is named after Clodoald, grandson of Clovis, who is supposed to have sought refuge in a hamlet on the Seine near Paris, then named Novigentum .. .. wonder what its relevance here !!

Do you love travel by train ? - ~ Railways, the Nationalised Career has a statue and does carries animals too .. .. the Railways responsibility as a carrier is as per Indian Railways Act 1989.  For loss or damage to goods carried as cargo – Railways is responsible – however, where the value of the cargo is not declared to carrier and  %age charge is not paid; the monetary liability of the railway has been limited to a measly Rs.50/- per kilogramme. 

The kilogram or kilogramme (symbol: kg) is the base unit of mass in the International System of Units (SI). Since 20 May 2019, it has undergone a quantum change is the subject matter of this post ! The kilogram is a unit of mass, a property corresponding to the common perception of how "heavy" an object is. Mass is an inertial property; that is, it is related to the tendency of an object at rest to remain at rest, or if in motion to remain in motion at a constant velocity, unless acted upon by a force.While the weight of an object is dependent on the strength of the local gravitational field, the mass of an object is independent of gravity, as mass is a measure of the quantity of matter. Because at any given point on Earth the weight of an object is proportional to its mass, the mass of an object in kilograms is usually measured by comparing its weight to the weight of a standard mass, whose mass is known in kilograms, using a device called a weighing scale. The ratio of the force of gravity on the two objects, measured by the scale, is equal to the ratio of their masses.

The gram, 1/1000 of a kilogram, was provisionally defined in 1795 as the mass of one cubic centimetre of water at the melting point of ice. The final kilogram, manufactured as a prototype in 1799 and from which the International Prototype Kilogram (IPK) was derived in 1875, had a mass equal to the mass of 1 dm3 of water under atmospheric pressure and at the temperature of its maximum density, which is approximately 4 °C.The kilogram is the only named SI unit with an SI prefix (kilo) as part of its name. Until the 2019 redefinition of SI base units, it was also the last SI unit that was still directly defined by an artefact rather than a fundamental physical property that could be independently reproduced in different laboratories. The IPK is rarely used or handled. Copies of the IPK kept by national metrology laboratories around the world were compared with the IPK in 1889, 1948, and 1989 to provide traceability of measurements of mass anywhere in the world back to the IPK.

With the definition of the ‘kilogram’ getting a global, technical makeover, textbooks — from those used in schools to ones recommended by engineering colleges in India — are set to undergo an update.Until Monday [20.5.2019], the kilogram derived its provenance from the weight of a block of a platinum-iridium alloy housed at the International Bureau of Weights and Measures in France. All other prototypes that served as national reference standards, including the one at New Delhi’s CSIR-National Physical Laboratory (NPL), were calibrated to it. No longer.On May 20, the kilogram joined other standard units of measure such as the second, metre, ampere, Kelvin, mole and candela that would no longer be defined by physical objects.

The measures are all now defined on the basis of unchanging universal, physics constants. The kilogram now hinges on the definition of the Planck Constant, a constant of nature that relates to how matter releases energy.The kilogram isn't a thing anymore. Instead, it's an abstract idea about light and energy.As of today (after May 20), physicists have replaced the old kilogram — a 130-year-old, platinum-iridium cylinder weighing 2.2 pounds (1 kilogram) sitting in a room in France —— with an abstract, unchanging measurement based on quadrillions of light particles and Planck's constant (a fundamental feature of our universe).

In one sense, this is a grand (and surprisingly difficult) achievement. The kilogram is fixed forever now. It can't change over time as the cylinder loses an atom here or an atom there. That means humans could communicate this unit of mass, in terms of raw science, to space aliens. The kilogram is now a simple truth, an idea that can be carried anywhere in the universe without bothering to bring a cylinder with you.And what? Practically speaking, the new kilogram weighs, to within a few parts per billion, exactly as much as the old kilogram did. If you weighed 93 kilograms (204 pounds) yesterday, you'll weigh 93 kilograms today and tomorrow. Only in a few narrow scientific applications will the new definition make any difference.

That cylinder in France would weigh much less if you brought it to the moon, and even a tiny bit more or tiny bit less if you brought it to other parts of the Earth. Not that reference any longer !It's not the easiest thing to stick on a scale. But, as an idea, it's a lot more portable than a cylinder of platinum-iridium alloy.What was 1 kg earlier is still 1 kg today.  If you had weighed 80 kgs a week before, you would not otherwise weight less or more than that.  You would be buying the same amount of brinjals @ 1 kg or 1 kg or rice.  All that has changed is the definition, for the sake of accuracy. A  mass measured as 1 kg earlier would have meant 1 kg, plus or minus 15-20 micrograms. Using the new definition, a mass measured as 1 kg will mean “1 kg, plus or minus 1 or 2 nanograms”.

For commoners like us, life has not changed at all – so we would continue to buy or measure anything with the same kilogram though there appears a quantum change in its definition.

Interesting or irrelevant or unable to make anything out of this !

With regards – S. Sampathkumar
21st May 2o19.

No comments:

Post a Comment