Question

you are on a sailboat in the ocean and watch other boats sailing away from you. eventually, the other boats seem to disappear completely past the horizon, but you know that they havent actually disappeared. how does this prove that earth is round?
type your answer here.

Explanation:

When a boat moves away, the curved surface of the Earth blocks the line of sight gradually. The bottom of the boat disappears first, then the rest, until it seems gone over the horizon. If Earth were flat, the boat would just shrink in size but remain fully visible as it moved away, rather than seeming to sink below a horizon line. This gradual occlusion matches the behavior expected from a spherical (round) planet.

Answer:

This proves Earth is round because the curved surface of the Earth blocks the line of sight to the boat gradually (the lower parts disappear first) as it moves away. On a flat Earth, the boat would only appear smaller but stay fully visible, rather than seeming to sink below the horizon.