6.79 mobility. Analogous mobilities are defined as the ratios of the following complex amplitudes:
- mechanical mobility ZM =velocity across/force through;
- rotational mobility ZR =angular velocity across/torque through;
- acoustic mobility ZA =volume velocity across/sound pressure through;
- electric impedance Z =voltage across/current through.
- The real part of each mobility is called responsiveness and the imaginary part the excitability. The reciprocal on any mobility is an immobility whose real part is unresponsiveness and imaginary part is unexcitability.