  This paper provides a new perspective to understand existing controversy on
the social force model. These issues include that the social force disobeys
Newton 3rd Law, oscillation phenomenon when one agent is approaching another as
well as some questions on the faster-is-slower effect. From the perspective of
physics these problems seems difficult to explain. This paper provides a new
perspective to understand these issues. We introduce a new concept of desired
interpersonal distance to explain how the social force is generated from
conscious mind of human. Although the social force disobeys Newton 3rd Law, the
whole model is exactly within the Newton Laws to characterize pedestrian
motion. The oscillation phenomenon may exist in non-physics entity (i.e.,
desired velocity and desired interpersonal distance) rather than physics entity
(i.e., actual velocity and actual distance), and such oscillation is mitigated
by treating non-physics entity as variable rather than constant. Very
interestingly, the desired velocity represents the motivation level of
pedestrian motion, and the faster-is-slower effect is thus explained by
Yerkes-Dodson law, explaining how motivation level could improve or impair
human performances in a collective sense. This inverted-U effect is further
studied with a falling-down model and the numerical testing is exhibited by
using FDS+Evac.
