The glob of mass starts off in motion at T0, there is no time prior to T0 in which a glob of mass exists waiting to be nudged.
Think of it like a particle decaying - at some point it just happens with no trigger or internal mechanism, and now you suddenly have the decay products wizzing about with some energy and momentum that they just start with.
Think of it like a particle decaying - at some point it just happens with no trigger or internal mechanism, and now you suddenly have the decay products wizzing about with some energy and momentum that they just start with.