Please explain my question like I'm 5 too? ELI5: Why do ships have circular windows instead of square ones? : explainlikeimfive

The real answer is that shapes with sharp corners are structurally weak. Arcs and circles are very strong shapes. If port holes were squares, the openings would get damaged and worn out sooner.

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    $\begingroup$ What did you find not clear in the answer? It is all mentioned: radiusing, fatigue, the comet ircraft etc plenty to drive your further research. $\endgroup$
    – Solar Mike
    Aug 2, 2020 at 6:41
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    $\begingroup$ An internal corner produces a stress concentration, so local stress is well above the nominal stress. $\endgroup$ Aug 2, 2020 at 15:09
  • $\begingroup$ See: en.wikipedia.org/wiki/Stress_concentration $\endgroup$
    – Ferdi811
    Aug 2, 2020 at 16:04

1 Answer 1


Stress is a physical quantity that averages over internal forces (e.g. van der Waals forces, Ionic bonding, collisions, ...) that neighbouring atoms/molecules of a material exert on each other.

If a force acts on an object, it causes stress inside the material. Stress behaves like a fluid in the sense that stress flows trough the material. Now, if there is a sharp corner, stress can't flow around it which causes a concentration of stress in that point.

If the stress in that region is to high, the material will fail. Therfore having round corners instead of sharp corners can make a structure stronger. The following picture from Wikipedia illustrates this quite well:

Picture from Wikipedia illustrating the flow of stress

  • $\begingroup$ See here in turn for a discussion of what those mysterious lines are intended to mean. $\endgroup$ Aug 4, 2020 at 21:38

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