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Why are Manhole Covers Round?

Physics | 7-14 yrs | Reading Pod

If you are the kind of person who likes to observe your surroundings while walking, you must have observed that most manhole covers are round.

But what’s the reason behind this? There ought to be some logic, right?
Well yes. Thankfully, there is a very sound logic behind this.

Let’s now take a look at some of reasons behind the round shape of manhole covers.

1. Compression of the earth

Like we know, the earth goes through different kinds of stress due to which it experiences compression. Under these circumstances, the circular shape of the manhole cover proves to be the best at resisting the earth compressing around it.

2. Carrying them around

It won’t be an understatement to say that manholes covers are heavy. These covers are made of cast iron, concrete or a combination of the two. This results in the average weight of a manhole cover range anywhere between 113 to136 kilograms! To move such heavy objects around becomes quite a problem. The circular shape of the covers ensures that less effort is involved as workers can just roll them to the required place.

3. Vehicles can move around conveniently

If the manhole covers do not have any sharp edges, cars can be safe from obstruction at all times. A manhole cover with sharp edges could easily poke the wheel of a car or get in the way. But it is far less likely for a circle to obstruct the movement of a car.

4. Easy to slip into place

A circle has no edges. This makes it possible for a round manhole cover to be easily slipped into place without much thought. In the case of all other shapes, the workers will need to line-up the covers with angles which makes the process quite cumbersome.

5. Easy to make

It is much easier to pour hot metal into a circular mold than one with sharp corners. Therefore the circular manhole covers are simpler to make as well.

6. Can’t fall through

Lastly, the most important reason behind the circular shape is that it will not fall through into the manhole. If another shape is used for the cover of the manhole it could fall into the hole if inserted diagonally. It is in fact only a circle that will not fall through into the hole.

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