I wonder whether there is a material which consists from individual molecules (that is, fluid), which has its angle of repose thus exhibiting propertes of a powder?


2 Answers 2


A liquid by definition has no fixed shape and therefore can have no angle of repose. I have noticed you have asked a similar question on Physics.SE; the presence or absence of this kind of property can be used as a means to classify powders versus fluids.

Note also that the conical "fixed shape" observed in powders is due to frictional forces between the particles, whereas any surface curvature in liquids from surface tension (e.g., a meniscus) is due to intermolecular forces between individual molecules.

Furthermore, take into account the melting point of the substance: it's a powder if the temperature of interest is below the melting point, and a liquid if it is above.


Such materials are called Bingham plastics. An angle of repose means that the material must withstand a non-zero shear stress (from its own weight) while still exhibiting zero shear rate.

Examples include toothpaste, ketchup, mayonnaise, latex paint, and concentrated suspensions of coal particles in a otherwise newtonian liquid. I'm not sure if any of these materials meets your requirement that it consist "of individual molecules". I don't think a single-component, single-phase, non-polymeric substance will ever exhibit Bingham plastic behavior, although (I might be wrong and) I can't cite any theoretical reason why this is so.

  • $\begingroup$ Do they really have angle of repose? $\endgroup$
    – Anixx
    Jul 9, 2015 at 17:24
  • $\begingroup$ Imagine a large tank of ketchup. You stick a one end of a long pipe straight into the surface of the ketchup, and let the other end be a large height above the bulk surface. Fill the pipe with ketchup, and after it is full, remove the pipe. The large column of ketchup will collapse into the bulk, but not completely. There will be a small pile left that will have some maximum angle w.r.t. the bulk surface normal. Isn't that an angle of repose? $\endgroup$
    – Curt F.
    Jul 9, 2015 at 18:09

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