A sewer cover always has a round shape, but is never triangular or polygonal. I would like to know the reason for this.
Answer
Dear Frank,
The shape of the sewer cover has been chosen in such a way that the cover can never accidentally fall down through the sewer opening. This is possible with many other forms. For example, you can pass a square lid through a square opening with the same dimensions by tilting the lid and letting it go along the diagonal of the opening. Since the diagonal of a square is greater than its side, it succeeds. This is not possible with a circle or a triangle. Triangular sewer covers are not very useful because it is more difficult for a person to pass through than through a round hole.
Another advantage of round lids is that they can be rolled. So it takes less effort to move them.
Kind regards,
Philippe
Answered by
Prof. Philippe Cara
Math
Avenue de la Plein 2 1050 Ixelles
http://www.vub.ac.be/
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