3 ms·
Boat speed is measured in knots. Knots are non-SI, since they're based on the non-SI nautical mile (1 knot = 1nm/hr). But they are a good example of why contex
by ubernostrum 14y ago
Boat speed is measured in knots.
Knots are non-SI, since they're based on the non-SI nautical mile (1 knot = 1nm/hr). But they are a good example of why context is important; the nautical mile is absolutely superior to the kilometer for use in navigation (at sea or in the air). Forcing the SI unit there would actually make the relevant tasks more complex and more difficult.
- guard-of-terra 14y ago"the nautical mile is absolutely superior to the kilometer for use in navigation (at sea or in the air)." Why is that?
- ubernostrum 14y agoIt solves headaches that come from trying to project the not-flat earth onto flat charts. As Wikipedia puts it: "In most projections, scale varies with latitude, so on small scale maps, covering large areas and a wide range of latitudes, the linear scale must show the scale for the range of latitudes covered by the map." "Mariners generally use the nautical mile, which, because a nautical mile is approximately equal to a minute of latitude, can be measured against the latitude scale at the sides of the chart."
- cygx 14y agoOn earth, the meridian has an approximate length of 20,003.93m. 20,003.93km / 180 / 60 ≈ 1,852.22m ≈ 1,852m = 1NM Note, however, that 20,003.93km / 200 / 100 ≈ 1,000.20m ≈ 1,000m = 1km so if we used gradians/gon where the full turn corresponds to 400 instead of 360, the kilometer would be an approximation as good as the (international) nautical mile.