  If there were nothing in bodies but extended mass and nothing in  motion but change of place and if everything should and could be  deduced solely from these definitions by geometrical necessity, it  would follow … that upon contact the smallest body would  impart its own speed to the largest body without losing any of this  speed; and we would have to accept a number of such rules which are  completely contrary to the formation of a system. (DM 21/AG 53–54)