- #36

dRic2

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I naively think that if you have a system of particles Newton's 2nd law says ##\sum_i \dot p_i = F_{tot}## so, assuming the system to be isolated, you get that the total momentum is conserved. In a scattering event this implies ##(m_1v_1 + m_2v_2)_1 = (m_2v_2 + m_2v_2)_2##. Do I have some terrible misconception ?vanhees71 said:How so? You have to make an assumption about the forces to get momentum conservation. The 1st and 2nd law don't tell anything about the forces!