Can you start a process before Shabbat that continues on its own during Shabbat?
Permissible: start before Shabbat, let it finish passively on Shabbat. The key is no active participation on Shabbat itself.
Question 2
Why might running a noisy mill on Shabbat be prohibited even if started before?
Marit ayin: it appears to observers that you're performing forbidden labor on Shabbat. Public perception matters in halachah.
Question 3
What is "shehiyah" in the context of Shabbat food preparation?
Shehiyah: leaving food on a heat source from before Shabbat. The food must be at least partially cooked (or the fire covered/reduced) to prevent the concern that you might stoke the fire on Shabbat.
Question 4
Can you place raw food on a fire right before Shabbat and let it cook?
Raw food on an open flame risks you stirring or adjusting it on Shabbat. It must be at least partially cooked, or the fire must be covered/diminished (chazarah/shehiyah rules).
Question 5
What is the key principle distinguishing permitted pre-Shabbat setup from prohibited action?
The distinction is active vs. passive: you may not actively do or continue labor on Shabbat. But a process set up before that runs on its own is permitted.