how is basic quantity calibrated?

Question

Let's say the calibration of length, mass and weight

Answer 1

Units are arbitrary, but once chosen need to be kept as a constant reference to allow comparison of results over time. This is a challenge, because even things like measurement precision change.

The original metre for instance was a reference bar of platinum held in Sevres, France - its length was originally chosen to be one ten millionth of the distance from the Equator to the North Pole on a line through Paris. Similarly for all other units.

These days, most units have been redefined in terms of unchanging physical phenomena that can be reproduced in any standards lab without the need for a special reference bit of metal. So the metre is now defined as the distance travelled by light in 1/299,792,458 seconds. This means it is a tiny bit different to the original metre but will never change.

The notable exception is mass. The kilogram is defined as being equal to the mass of the international prototype of the kilogram. This prototype is a lump of platinum iridium alloy held in Paris. The kilogram is the only SI unit based on a reference prototype.

Answer 2

Do you mean how are the SI units defined? {i.e. What does 1 kilogram mean?}

For mass: The kilogram {a weight equal to a metal weight kept under 3 bell jars on the basement of a museum in Paris}

Meter: The distance between a certain number of wave peaks of a very specific type of lazer.

Weight: Weight is simple mass {kg} mulitplied by acceleration due to gravity {m/s^2}. Weight is the force an object exerts downwards. It is simply a force {measured in Newtons}

Answer 3

The International System of Units (abbreviated SI from the French language name Système International d'Unités) is the modern form of the metric system. It is the world's most widely used system of units, both in everyday commerce and in science.

Answer 4

The International System of Units (abbreviated SI from the French language name Système International d'Unités) is the modern form of the metric system. It is the world's most widely used system of units, both in everyday commerce and in science.