On what basis can it be argued that a body composed of two identical parts has a mass twice the mass of each part?

Human experience has proven that mass is an additive quantity, that is, the mass of a body composed of two bodies is equal to the sum of the masses of these bodies.
Let us denote by m – the mass of the component, M – the mass of the body, then:
M = m + m = 2m.
Let’s find their relationship:
M / m = 2m / m = 2.



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