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I am quite amazed by this observation as I couldn't prove it or intuitively have a correct reasoning for the circular geometry of the water drop which it acquires while getting absorbed on a bed sheet.

The tag on the bed sheet is printed by a statement that threads are made up of 100% cotton material.

Why the droplet tends to acquire a circular shape rather than acquiring any other shape?

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  • $\begingroup$ By circular symmetry. At least locally the water droplet can't tell the difference between any particular direction so it treats each as the same. This results in the droplet appearing circular when it spreads on the bedsheet. $\endgroup$ – PhysMath Jun 19 '19 at 18:36
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The water drop is compelled by surface tension to adopt a globular shape, as this has the maximum volume for the least surface area. When it hits the sheet, the wet patch is circular, and capillary action causes the moisture to spread out equally in all directions, so the final damp spot is circular also.

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    $\begingroup$ If the weave is different in the two directions will that change the shape? $\endgroup$ – user207455 Jun 19 '19 at 19:16

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