A normal adult-size figure and three metres divided into centimetres
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Physics -- Units and Concepts: Space |
The most basic space measure is distance or length. The unit is the metre, or m.
A normal adult-size figure and three metres divided into centimetres
One hundredth of a metre is a centimeter, cm, used only for convenience. The normal smaller unit is 1/1'000 of a metre, called a millimetre, mm. Again 1'000 times smaller is a micrometre or micron, µm. There are a million microns in a metre.
The larger unit is 1'000 m or 1 kilometre, km.
An aerial view north of Geneva, showing the airport's runway, 4km long.
The bright green line marks a length of 1km. (photo CERN, European Organization for Nuclear Research)
Again larger is 1'000 km, which we should call a megametre, 1Mm, but somehow nobody does that. Perhaps because the Earth is not large enough. The length of the metre was derived from the size of the Earth though: it was defined as the ten-millionth part of a quarter of the circumference.
The red segment shows one quarter of a meridian.
Dividing its length by ten million gives you one metre.
If one quarter is 10'000'000 m, that is 10'000 km. Then the circumference of the Earth should be 40'000 km, by definition. Unfortunately, the brave people who went out to actually measure the Earth used a meridian. Later it was found that the Earth is slightly flattened because it turns around. The equator is therefore a bit larger than expected: 40'072 km around.
If we want to measure surface, we use square metres or m2. A few units used in land surveying are:
For volume we use cubic metres or m3. But that is a rather large quantity, we want something smaller.
A virtual cubic metre in my living room
Take a cube of one metre side. Divide each side by ten and cut the cube up like that, forming 1'000 smaller cubes, each of side 10cm:
One such smaller cube is a litre. There are a thousand litres in a cubic metre. Milk is sold in 1litre packs, but they are not cubes.
A 1litre milk pack.
