Question

when does substance flow?
please answer it...​

Answer 1

$\sf\red{Answer:-}$Material flow analysis (MFA), also referred to as substance flow analysis (SFA), is an analytical method to quantify flows and stocks of materials or substances in a well-defined system.

Answer 2

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Most of the materials flow because its particles and molecules do not form a rigid and definite arrangement at normal temperature and pressure. This is the basic property of materials that allow it to flow as against the solids where the particles and molecules are strongly and rigidly bounded together