For F = (y, −x, 0), compute divergence and curl. ∇·F = ∂(y)/∂x + ∂(−x)/∂y + ∂(0)/∂z = 0 + 0 + 0 = 0. ∇×F = (∂(0)/∂y − ∂(−x)/∂z, ∂(y)/∂z − ∂(0)/∂x, ∂(−x)/∂x − ∂(y)/∂y) = (0, 0, −1 − 1) = (0, 0, −2). Zero divergence (no source), nonzero curl (rotation about z-axis) — like a whirlpool.