Just read somewhere that the shortest path between two locations is an arc and not a straight line! eli5 how an arc is the shortest path for planes.
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there’s no such thing as a straight line on a map. Any straight line on a map, if attempted in real life, would actually have to cut through the middle of the planet then come out on the other side.
So it has to be an arc since a straight line is impossible. Planes can’t plow through the earth’s mantle, they have to fly in an arc across the surface. Think of a fly going across the surface of a basketball.
You’ve misunderstood. The shortest path between 2 points is *always* a straight line. It’s just that on a flat map that represents a sphere, that line looks like an arc, and on the surface of the sphere, the line follows the curve of the sphere (but it’s still a straight line).
https://en.wikipedia.org/wiki/Great-circle_distance
https://www.greatcirclemap.com
Great Circles, which you asked about are a circles around the Earth whose center is in the Earth center. When ships/planes for example do long trips they follow a Great Circle route which is the shortest way. This means that you have to change the course repeatedly during the trip. This is clearly visible when you see a Great Circle represented on a 2D map.
If you have access to a physical (round) world globe map you can take a piece of yarn, place the ends on two locations (with yarn being tight). The yarn is then part of a great circle that goes through both locations and it is the shortest distance between those locations.
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