Depth 1 · 39 s
A piece of the Earth
In 1791 France took a new unit of length from the Earth itself - the distance from the North Pole to the equator, split into ten million parts. One part is a metre. Then 100 centimetres, 10 millimetres in each, and 1,000 metres in a kilometre - which is why the Earth is about 40,000 km around.
About this video
Why is a metre the length it is? In 1791, during the French Revolution, scientists in France decided that the new unit of length should come from something that belongs to everyone: the Earth itself. They defined the metre as one ten-millionth of the distance from the North Pole to the equator, along the line through Paris. One metre is about as long as a guitar.
This animation follows that idea and the units built from it. A metre has 100 centimetres and a centimetre has 10 millimetres, while 1,000 metres make a kilometre, about ten football pitches end to end. Because of how the metre was made, the distance from the pole to the equator is about 10,000 km, and the whole way round the Earth is about 40,000 km. That is no coincidence: a metre is a piece of the Earth. (Today the metre is defined by the speed of light, but it has kept the same length.)
This video shows depth 1 of Length.
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- 0:00Who decided how long a metre is?
- 0:04In 1791, France chose something everyone shares: the Earth.
- 0:09Pole to equator, split into ten million equal parts.
- 0:13One part is one metre, about as long as a guitar.
- 0:17A metre is 100 centimetres. A centimetre is 10 millimetres.
- 0:21And 1,000 metres make a kilometre: about ten football pitches.
- 0:25So pole to equator is 10,000 kilometres. Round the Earth: 40,000.
- 0:30Not luck. That's how the metre was made.
- 0:34A metre is a piece of the Earth.