The Street Manhole - Geometry Puzzle

Have you noticed the manholes along the street are circular in shape?
They are purposely made that way, though.

What's the reason?

The answer has to be explained through geometry in mathematics.

For a circle, the distance of its centre point to the outer edge is always a constant.
Comparing this to other type of shapes, for example, rectangle or hexagon, these other shapes do not have this characteristics.

If someone happens to close the lid of the manhole at a tilted angle, the shapes other than the circular one, has a possibility to drop through the manhole.

The circular-shaped lid will never has a chance to slide through and enter the manhole at all!

The constant radius of a circle ensured that there will not be any gaps in all possible condition between the lid and the manhole opening.

With this reason, the manhole are made circular in shape.

This theory relates geometry to problem-solving of real-world matters.

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