Editing Quantum turbulence (section)

=== Superfluidity ===
Superfluidity arises as a consequence of the [[dispersion relation]] of elementary excitations, and fluids that exhibit this behaviour flow without [[viscosity]]. This is a vital property for quantum turbulence as viscosity in classical fluids causes dissipation of kinetic energy into heat, damping out motion of the fluid. [[Lev Landau|Landau]] predicted that if a superfluid flows faster than a certain critical velocity <math>v_c</math> (or alternatively an object moves faster than <math>v_c</math> in a static fluid) thermal excitations (rotons) are emitted as it becomes energetically favourable to generate quasiparticles, resulting in the fluid no longer exhibiting superfluid properties. For helium II, this critical velocity is <math>v_c \approx 60 \text{m/s}</math>.