\frac{dL⃗}{dt} = τ⃗

dL⃗ = τ⃗ dt (L⃗_{f} − L⃗_{i}) = τ⃗ dt L⃗_{f} = L⃗_{i} + τ⃗ dt

|dL| = ( radius )( angle )

= (|L_{i}|) (dϕ)

|τ dt| = (|L_{i}|)  (dϕ)

|\frac{dϕ}{dt}| =