We review six different physical mechanisms that lead to alternating electric field induced flows in ferroelectric liquid crystals. Linear electromechanical effects are mainly caused by director rotation induced flows and by electroclinic induced variation of the layer spacing. Transient vibrations occur at fast field reversal due to "inverse electroclinic" which attracts the plates before the collective director rotation is activated. During full rotation of the director around a cone the pressure varies yielding vertical vibrations with higher harmonic components. Periodic fields also induce "pumping" effects. A pumping can be caused either by a flow parallel to the plates, or by an increase of the sample thickness. The unidirectional flow reflects the chirality of the system, whereas the increase of the sample thickness cannot be connected to the chirality.