Video: How we measure distance
Hello again. I’m Doctor Bruce Warrington, Australia’s Chief Metrologist.
Today I’m talking about the metre, one of the seven basic units of measurement. It took a long time to get an agreed measure of length.
The Egyptian cubit was the length of a man’s arm –depending on the man. The English inch was three pieces of barley end to end. And in the 1700’s every town in France measured length differently, a real problem for trade between towns and between countries.
France proposed a new metre tied to the Earth, one ten-millionth of the distance from the North Pole to the Equator. In 1875 seventeen countries adopted the metre, and made a special bar made out of platinum alloy to keep as the international reference standard.
Today pretty much the whole world uses the metre, but since 1983 it is defined as the distance light travels in 1/299 792 458 of a second. This definition uses the speed of light, a fixed constant of nature, and lets us measure precisely from the very big to the very small.
Here at the National Measurement Institute we can measure down to a nanometre, that’s a billionth of a metre, almost a hundred thousand times smaller than a human hair. This means we can measure nanomaterials, and help Australian manufacturers make new nanotechnology products.
Thanks for listening, and stay tuned to hear about the other units of measurement!
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