The name "helicity" is because the trajectory of a fluid particle in a fluid with velocity v and vorticity ω ω = ∇ ∇ × × v forms a helix in regions where the kinetic helicity H K = ∫ ∫ v ⋅ ⋅ ω ω ≠ ≠ 0 . When H K > 0 , the resulting helix is right-handed and when H K < 0 it is left-handed. This behavior is very similar to that found concerning magnetic field lines.