That's the only shape that won't fall into itself :
Imagine you have a big hole in the ground, like a secret door to go underground where people need to work or fix things like pipes and cables. To cover this hole and keep it safe, you need something like a lid. Now, why do you think it's a good idea to make this lid round?
1. **Safety:** Well, when you have a round lid, like a big, flat circle, it can't fall into the hole by accident because it's the same shape as the hole. Imagine trying to put a square or a triangle lid on the hole. It might wobble or fall in if it's not positioned just right. A round lid stays put, making it safer for everyone.
2. **Easy to Open:** When workers need to get inside the hole, like when they have to fix things underground, it's really easy to lift a round lid. They can roll it to the side, and it won't fall back into the hole because it's round and won't get stuck.
3. **Everywhere the Same:** Another cool thing about round manholes is that they look the same all over the place. That's because most manholes are round, so it's easier for people to know what to do when they see one. It's like a secret code that everyone understands.
So, in simple words, manholes are round because it's safer, easier to use, and everyone knows what to do with them. It's like having a special shape for a special job!