system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do planes and boats use the same unit for distance. Maybe the question would be why do they both use knots?
gpt
Knot is not a unit of distance but a unit of speed (Distance divided by time).

A knot is a short way of saying one nautical mile per hour.

A nautical mile is how ships (and aircraft) measure the distance they travel. One nautical mile is exactly 1852 meter.

Nautical miles are conceptually related to meters and kilometers as one nautical mile is the distance of one minute of latitude. A minute of latitude is a 60th of a degree (the same as a minute of time is one 60th of an hour) and there are 360 degree in a circle.

Thus a nautical mile was originally defined as being one (60 x 90) part of the distance between the equator and a pole, while a kilometer was originally defined as 1/10000 of the distance between the equator and the pole.

The name knot originally comes from ships measuring their speed through the water by having a rope with literal knots on it unspool into the water to see how fast they are going.

Today it is used to mostly describe the speed of a vessel though a medium like water or air, but in theory since it is just a measure of speed you can also use it to describe how fast your car is going (but nobody does that).

It use today is mostly down to tradition rather than any practical use. The navigation equipment and other modern devices used to measure speed of ships and planes etc today could just as easily display the result in any other value, but knots and nautical miles is what we have gotten used to.