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This is freshly ground pepper on water.

Why is there a triangular configuration of the water around the pepper fragment? Surely all these pepper fragments have different shapes? You can clearly see one of these triangles on the lower left edge of the reflection of the kitchen light.


(source: maresh.info)

With pepper, this configuration doesn't last long, the fragments clump.

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    $\begingroup$ Sorry, for me it is not really obvious what you mean from the picture. I think I need more zoomed/better focussed picture... $\endgroup$ – Bernhard May 30 '14 at 7:18
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    $\begingroup$ The particles of a ground pepper definitely aren't spherical or in any way symmetric. It's possible that after reorientation under gravity, three-faced corner vertices are the most common. However, it could also be nonuniform lighting. Does the light have multiple bulbs? $\endgroup$ – orion May 30 '14 at 20:50
  • $\begingroup$ Possible duplicates: physics.stackexchange.com/q/139607/2451 , physics.stackexchange.com/q/71292/2451 , physics.stackexchange.com/q/55833/2451 and links therein. $\endgroup$ – Qmechanic Dec 14 '14 at 7:44
  • $\begingroup$ This is not a duplicate, @QMechanic! This concerns the arrangement of surface tension immediately around the pepper fragment! $\endgroup$ – graveolensa Dec 14 '14 at 15:53
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My best guess is that your basic assumption, that all pepper fragments have different shapes, is wrong.

The water is indented at the pepper fragment because gravity acts on it downward. Without surface tension the pepper would sink because of that. The surface tension of the water-air interface however, is strong enough to withstand the force downwards, resulting in a force balance, but at the cost of a certain degree of curvature. (see also this Physics.SE question)

The indentation of the water is a response to the gravitational pull on the pepper fragment, therefore the only reason for the triangular symmetry that you observe can be the shape of the pepper fragment. Apparently these fragments are all (roughly) triangular, which might be a consequence of the specific way that they were ground.

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    $\begingroup$ The average burr grinder functions in such a way as to leave the fragments with mostly concave faces. These faces would be where the pepper rests against the water, and they would overwhelmingly rest across three points at a time. Getting a coplanar fourth (or more) point would be very rare out of a random grinder, so almost all "resting faces" would be triangular. $\endgroup$ – Asher Jun 26 '16 at 8:36
  • $\begingroup$ @Asher great comment, you should consider writing this up in an answer $\endgroup$ – Sergei Patiakin Aug 31 '16 at 14:11

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