The main aim of the present paper is to prove the possibility of the phenomenon of antigravity. As is shown by the example of plane curvilinear motion, the material bodies moving by inertia can repel each other. According to the criterion of antigravity obtained, the necessary condition for antigravity is the motion of a body by inertia along such a curvilinear trajectory on which the energy of the body is transferred from the rotational degree of freedom to the translational one. A control parameter with the change of which the character of particles motion changes is introduced. When the control parameter passes through some critical value, the force of attraction between particles is replaced by the repulsive force. Thus, the possibility to control the character of interaction between the particles of a physical system by redistributing the energy of the system between its degrees of freedom is unclosed. It is shown that the extension of the Newtonian scheme of mechanics by taking into consideration a broad class of curvilinear motions by inertia demands the refinement of the standard notion of inertia of the material body. The concept of inertia property should reflect the presence of dialectically opposite components of motion, associated with conservation of two characteristics of body motion - momentum and kinetic energy representing, accordingly, the force and energy measures of motion, mutually supplementing each other. The inertia property of body is that any body opposes to changing both momentum and kinetic energy. The tendency of the body to conservation of momentum leads to the uniform and rectilinear motion (i.e. to translational inertia), and the tendency to the kinetic energy conservation – to the curvilinear (accelerated) motion by inertia. Both types of inertial motion have a general feature - they can continue unrestrictedly long. The material bodies, moving along a curvilinear trajectory by inertia, are shown to generate electromagnetic field in environment. This field can be considered as a special physical medium which is created by bodies when they move with acceleration by inertia and is capable to exert back action upon bodies. The results of the investigation presented in this paper allow one to make a guess that electromagnetism, as well as gravitation, is not a special kind of interaction. Electromagnetism is the interaction of material particles with mass that are in such states of curvilinear motion by inertia in which energy is transferred from some degrees of freedom to others.