Negative mass and elasticity

The paper introduces the concept of equivalent mass and elasticity. The physical sense of their negative values is explained, and it is demonstrated that they do not contradict the laws of conservation of energy and impulse. Formulas are introduced to calculate the energy of equivalent mass and elasticity. The limits on the character of their frequency dependences are formulated. In particular, it is noted that it is impossible for negative mass and elasticity to be independent of frequency.