  A simplistic model, based on the concept of anankeon, is proposed to predict
the value of the viscosity of a material in its liquid phase. As a result,
within the simplifications and hypothesis made to define the model, it is
possible to predict (a) the existence of a difference between strong and
fragile liquids, (b) a fast variation of the viscosity near the glass
transition temperature for fragile liquids. The model is a mechanical analog of
the Drude model for the electric transport in metal.
