Internal Friction—is the friction between the fluid elements and in principle it can either laminar or turbulent though for all practical purposes friction in the ocean is due the interaction of turbulent eddies. In laminar flow (movie in class) friction arises due to the actual rubbing of molecules— and the frictional force is equal to the density times the kinematic viscosity times the vertical

τ=ρν ∂ v∂ z

where is the molecular kinematic viscosity of sea water where has a value of 1*10-6 m2/s (note those units—we’ll talk about them later). We’ll see later that turbulent friction, while considerably more complicated can be expressed in an identical form expect is replaced with the turbulent eddy viscosity (Av) also with unites of m2/s--what makes turbulent friction more complicated is that Av varies by orders of magnitude in the ocean depending on the state of the flow. This then requires a closure

τ=ρA v∂ v∂ z