  Active particles which are self-propelled by converting energy into
mechanical motion represent an expanding research realm in physics and
chemistry. For micron-sized particles moving in a liquid ("microswimmers"),
most of the basic features have been described by using the model of overdamped
active Brownian motion. However, for macroscopic particles or microparticles
moving in a gas, inertial effects become relevant such that the dynamics is
underdamped. Therefore, recently, active particles with inertia have been
described by extending the active Brownian motion model to active Langevin
dynamics which include inertia. In this perspective article recent developments
of active particles with inertia ("microflyers") are summarized both for single
particle properties and for collective effects of many particles. There
include: inertial delay effects between particle velocity and self-propulsion
direction, tuning of the long-time self-diffusion by the moment of inertia,
effects of fictitious forces in non-inertial frames, and the influence of
inertia on motility-induced phase separation. Possible future developments and
perspectives are also proposed and discussed.
