The Halakhah recognizes the effects of one’s actions (kocho) as well as the effects of those effects (koach kocho). The Ohr Sameach asserts that in several areas of Halakhah, koach kocho is not equivalent to kocho, to thus attach to the original action. He includes Shabbat in this category; although one is liable for throwing an object into a public domain (kocho), this would not hold true in a situation of koach kocho.

One gets a different impression from Tosafot (Shabbat 99b, s.v. oh). There, the Talmud inquires as to the liability of one who throws an object onto a (10x4) pillar from a reshut ha-rabbim. Perhaps, since it passed through a m’kom p’tur, the thrower is exempt. Tosafot, quoting Rabbeinu Tam, explain that the scenario is such that the object paused in the m’kom p’tur, interrupting the original koach. The implication is that the potential exemption stems from the interruption; had the “koach” led right into a “koach kocho” there would have been liability.

The Rashash, however, notes based on Sanhedrin 77b that such a process would actually be called “kocho”. The intent of Tosafot, then, was not to address the issue of kocho or koach kocho, but to note that the “koach” would be considered to have emanated from the m’kom p’tur only if the item paused there. (See also R. Shlomo Fisher’s Beit Yishai, 78, for a lengthy analysis of this topic, and also Resp. Eretz Tzvi, I, 112.)