Swirlet

Meet Swirlet, a cloud who tries to drift straight but keeps curving, because the Earth turns beneath him.

On a spinning planet, anything moving across the surface seems to be pushed sideways. Nothing is really shoving it. The ground underneath is turning while the cloud keeps moving in a straight line through space. In the Northern Hemisphere the path bends to the right, and in the Southern Hemisphere to the left.

The size of the sideways acceleration is a = 2Ωv sinφ, where Ω = 7.29 × 10⁻⁵ rad/s is the Earth's spin rate and φ is the latitude. Air moving at 10 m/s at 45° latitude gets a ≈ 1.0 × 10⁻³ m/s².

That is tiny, but over an hour it would bend a path by several kilometres. At the equator sinφ = 0 and the effect vanishes.

Over thousands of kilometres it sets the giant spin of hurricanes and the great ocean currents. It is far too weak to decide which way your sink drains.