Why do we use knots as a speed measurement unit for air and water travel?
In: Engineering
Nowadays mostly for historical reasons. Converting everything to metric would require changing a ton of infrastructure.
Why nautical miles and knots were defined differently from land miles: 1 nautical mile is 1 minute of equatorial latitude, so it’s very handy for estimating distances, travel times, etc. from coordinates without any computing tools other than your brain. Vital for seafarers well into mid-20th century and still used as backup nowadays, GPS navigation is very recent and can be disrupted.
The world is not flat. The world is round and this is how we properly account for the curvature of the earth. When you travel short distances ( a few miles) you don’t really need to account for the curvature but when you travel long distance, you have to.
It is also kinda useful, since 1 knot is 1/60th of a degree of latitude. For things that travel far enough where you cross the lines on the globe, it can be handy.
More than anything though, it’s one of those things that’s just hard to change because it started so long ago. It goes back to ships in the 17th century. It was the unit of measure for some of the only things that went fast or far enough for us to care about how fast they were going. Pre cars, pre trains, pre airplanes. It has been engrained in aviation and boating industry since before America was a country.
The nautical mile makes calculating distance traveled at sea comparatively easy. Mariners in the age of sail could figure their latitude and longitude well enough (eventually), which makes it straightforward to figure distance in degrees. The NM sets an easy conversion for that, defining a mile as being one arc minute latitude, so 60 nm to a degree.
That we still use it is as much to tradition as anything.
In olden times, sailors had a rope with knots tied in it every 47ish feet. And they tossed the rope off the side of the boat, and then measured how many “knots” a point of the boat passed in a given period of time. And that was how they measured boat speed in the age of sail, is by counting knots on a rope.
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