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In this work, the mechanism behind motion in closed systems is investigated by studying two simple mechanical systems. Firstly, a simple “ballistic” car system introduces the subject of propulsion as a function of a parameter that modulates the amount of ejected mass, thus allowing a transition between a closed to an open system. The second example provides a physically realizable (and optimizable) system, in which a mass sliding on the internal surface of a mechanical wheeled cavity is shown to produce a net movement, provided that dissipation is present. Several additional ways are discussed by which to ‘open’ a system whilst keeping the mass constant. As a function of strict momentum conservation, it is concluded that both internal mass motion and dissipation are key factors in the only way a mechanical system can move itself in a weak sense, in contrast to a strong meaning of ‘self-propulsion’.

Dissipation and mass redistribution as a mechanism of propulsion in closed systems