Fig. 1. Outline of the physical process, (the near-field region is enlarged and the radiative area has been shrunk to ease reading).

When an electromagnetic wave, (for example a monochromatic plane wave, as illustrated here), impinges on a body, charges are separated, thus inducing multipoles. The object feels a time-averaged Lorentz force, RLF, associated to the field (i.e., Poynting) momentum flux, RMST, flowing into a far-field surface, (e.g., spherical as shown). However, there also appears a flow, IMST, of imaginary field momentum, related to momentum flux going back and forth across a near-field surface, with zero time-average, which accumulates reactive strength of orbital momentum, ROM, stored both inside and in the near-field of the object, yielding a reactive force, ILF, on the body