Q&A: Physics
Originally published:
This is an English translation (via GPT-5.4). Read the original Hebrew version.
Physics
Question
In several places in the Mishnah, a rule is brought that any vessel that lets liquid in also lets liquid out, but a vessel that lets liquid out does not necessarily let liquid in.
Why is that? (The amoraim disagreed about how this is tested, whether with the vessel upright or upside down, etc.)
Answer
Do you mean, for example, in Niddah 6b? It seems to me that, as a matter of fact, it is harder to get water in from the outside than to get it out. You don’t line up exactly with the hole, and so on. If you fill a vessel with water and it has a hole, the water will always leak out. But try filling a vessel with water through a small hole.
Discussion on Answer
It really is strange. I don’t know.
Page 49 there: Mishnah: Any earthenware vessel that lets liquid in lets liquid out. And there are some that let liquid out but do not let liquid in.
Our Rabbis taught: How does one test an earthenware vessel to know whether it was perforated enough to admit liquid or not? He should bring a tub full of water and place the pot inside it. If it takes in water, it is known that it admits liquid; if not, it is known that it lets liquid out.
Rabbi Judah says: He bends the handles of the pot into it and floats water over it, and if it takes in water, it is known that it admits liquid; if not, it is known that it lets liquid out. Or he places it on top of the fire: if the fire sustains it, it is known that it lets liquid out; if not, it is known that it admits liquid.
Rabbi Yose says: Not even by placing it on top of the fire, because the fire sustains it; rather, on top of hot ashes…
I’d be happy for an explanation.