2 ms·
How Did The Meter Get Its Length?
- ColinWright 12y agoRoughly ... They were going to use a length such that a pendulum would have a 1 second half period, or 2 second full period. That varies according to where you are, but it's pretty good. This means that g=(pi)^2, because the period of a pendulum T is given by 2(pi)sqrt(L/g). Since that varies according to the local value of g, they then used one ten-millionth ( 10^-7 ) of the distance from the North Pole to the Equator running through Paris. They actually did that by extrapolating a shorter distance, but it means the Earth is, "by definition", 40 million metres circumference. They created a platinum bar of the right length and declared that to be the answer. Turns out it's wrong, but they never bothered to fix it. However, in 1960 the eleventh CGPM defined the metre to be 1,650,763.73 wavelengths of the orange-red emission line in the electromagnetic spectrum of the krypton-86 atom in a vacuum. Obviously much easier to use.