Why do prevailing winds turn north in the hemisphere and South in the hemisphere?

Question

Why do prevailing winds turn north in the hemisphere and South in the hemisphere?

Answer 1

Because of the direction of the earth's rotation, and the earth's curvature.

The same thing affects the direction water takes when it forms a whirlpool going down the drain.

Basically any piece of ground is not flat. If you imagine a plane where you're standing, the ground will drop away from that plane on all sides. But there is an asymmetric difference. When the earth spins it is kind of like a centrifuge with the equator the outside. Newtonian inertia pushes an object directly outward in the plane of earth's rotation; in the northern hemisphere, this is also slightly to the south, because the ground there is not perpendicular to the plane of earth's rotation. In the southern hemisphere, it's to the north. This has an asymmetric effect on the motion of objects in each hemisphere. The only place newtonian inertia pushes an object in a direction perpendicular to the ground is at the equator.

btw you didn't specify which hemisphere trade winds go north in, and which one they go south in. But I was always under the impression that they all go north and south both, at various times. Maybe you mean clockwise, and counter-clockwise.