Question

why does a heap of sand or a hill have a pyramidal shape
Please answer

Answer 1

because when sand falls down freely it forms a pyramid shape

Answer 2

I think to be stable because of a broader base. If you place a pyramid on the floor at its apex, it will fall, but if you place it at its base it will stand. When you pour something like wheat or rice it first attains a broad base and then narrows to the top.