h i g h l i g h t s • We investigate the dynamics of a positive mass and a negative mass chain, which shows the two bodies may be self-accelerated in same direction. • We examine the self-accelerated motion of equivalent two-mass chain in experiment. • We show that the Hamilton's principle is applicable when the energy of the negative mass unit is properly characterized. a b s t r a c t We investigate the interaction between a positive mass and a negative effective mass through a threemass

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... connected with elastic springs, a pair of masses is designed to have an effective negative mass, and it interacts with the third positive one as if an equivalent two-mass chain. The dynamics of the equivalent two-mass chain shows that the two bodies may be self-accelerated in same direction when the effective mass becomes negative, the experiment is also conducted to demonstrate this type of motion. We further show that the energy principle (Hamilton's principle) is applicable if the energy of the negative mass unit is properly characterized. The result may be relevant to composite with cells of effective negative mass, their interaction with matrix may lead to more richer unexpected macroscopic responses.