The book tells about the state of weightlessness from a physical point of view. Previously, in order to give a sufficiently deep (but also quite popular explanation available to a layman), questions are considered about the essence of the force of inertia and forces of gravity, and their equivalence. The book can be seen as an interesting introduction to mechanics. The question of the state of weightlessness as one of the aspects of the problem of space flights will undoubtedly interest the widest circle of readers - from schoolchildren who have become classes to university students, teachers.