We will consider them equal in magnitude, since this result and the interest (and does not change the generality of the arguments). Then, the internal connection between these bodies begin to compensate for these interaction, all of this long and difficult. Without loss of generality, one body will be regarded as a charged particle A. Another body of D, as the two raznozaryazhennye particles B and C, which act on A – in fact they eletroneytalny for each other (and the number of particles was reduced to the limit). Arising from the interaction of speed and strength will assign a single particle A, since only interested in finite resultant force acting on A. Now we find 2).

Yet without clarifying the nature of the velocity: a slow speed u in D relative to a fixed A. Fixed position of a particle A (if there is no electrical interaction) is characterized by a certain point in space, which we call the expectation of A. In particle A may be the speed + v or separately-v (due to electrical interaction) relative to the stationary matrix. standby position A. If we now consider fixed D, then by the addition of velocities of STR obtain the velocity of A relative to D: w = (v + u) / (1 + vu / c ) is now in the formula for power (the expression of force through the momentum) we have an additional term: F = dP / dt, where P = P (w) – dependence pulse velocity w – we are interested only version of speed change in magnitude (see, for example, Landau and Lifshitz "Classical Theory of Fields" section: "The energy and momentum).