Small ε ε implies the collisional term C ^ ^ f dominates the streaming term v ⋅ ⋅ ∂ ∂ f ∂ ∂ r + F m ⋅ ⋅ ∂ ∂ f ∂ ∂ v , which is the same as saying the Knudsen number is small. Thus, the appropriate form for the Chapman–Enskog expansion is