(WYTV) – Manhole covers are round. Why?

That question has come up in job interviews. Look up the third edition of “The Complete Idiot’s Guide to Job Interviews” and you’ll find it.

Of all of the potential shapes for manholes, why was a circle chosen?

Larry Scheckel wrote a book called “Ask A Science Teacher” and here is his answer.

Manholes are round because it is the best shape to resist the pressure of the ground around it. Round shapes are easier to make than square or rectangular shapes, and because manhole covers are heavy, being round makes them easier to move from place to place by just rolling them along.

You need not line up a cover with any angles, just slip it into place.

But the biggest reason that manhole covers are round is safety. Round covers will never fall through a circular opening.

Scheckel writes that for all manholes, there is a ‘lip’ around the rim of the hole, holding up the cover.

That means the hole is always smaller than the cover, the cover always wider than the hole.

A square, a rectangular, or an oval manhole cover could fall in if you inserted it diagonally. You can’t when it’s round.