Actual agents go towards one thing as opposed to another, and so their action is toward an end.
We should never overestimate our powers to know what this end is- in most cases we do not know it, and we probably never will know it. We can only know that there is some end, not what the end is in particular.
In the case of the sorts of motions considered most “scientific”; i.e. inertial motions, chemical changes, energy conversions, etc, we have no idea what exactly the end is, and we perhaps never will. The reason for this is that inanimate things perform no action for their own sake, since such action is proper to living things. It is therefore unnecessary, and perhaps impossible, to say (for example) that some radioactive substance gives off isotopes for the sake of the radioactive substance, or that an inanimate object floating by in space is attaining some good for the floating object itself. Inanimate things have no selves, and therefore cannot act for themselves. See Questio disputata de anima a. 13 co. in inanimate things what happens is from some extrinsic agent, in living things, it is from some interior agent. The sense here is not that inanimate things are totally inert: St. Thomas knew about fire, lightening, magnets and falling stones. The sense is that the action of the inanimate does not constitute a self motion, which no one disagrees with. For an account of life as self motion, see Summa theologiae I q. 18 a. 3 co.