What about by network effects? Many less grains qualify as a heap by some threshold of heap-like behavior, by particulate physics, but otherwise isn't a heap.
A single grain can't interact with another grain, so it's not a heap. Two grains on a platform the size of one could slump, so maybe two make a heap:
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[ 3.3 ms ] story [ 11.7 ms ] threadA single grain can't interact with another grain, so it's not a heap. Two grains on a platform the size of one could slump, so maybe two make a heap:
https://en.wikipedia.org/wiki/Angle_of_repose