Book 25, Question 54 · Video
Why are manhole covers round?
A round cover cannot fall through its own hole, no matter how you turn it, because a circle has the same width in every direction. A square one could slip through diagonally. Manhole covers are heavy iron, sometimes 100 pounds or more, so they stay put under traffic. Workers use special hooks to lift them. Never try to open one.
Read the full answer →Watch on YouTubeSee the series on Amazon
What Crafty Clover says in this video
Intro
Hi there, curious minds! I'm Crafty Clover! Let's discover something amazing. Why are manhole covers round?
The Big Idea
Look down at a city street, and you will see round metal lids. They are manhole covers! Why are they round?
Same Width
Step one: Same Width. A round cover cannot fall through its own hole, no matter how you turn it. That is because a circle has the same width in every direction.
Square Trouble
Step two: Square Trouble. A square cover could slip through diagonally. The diagonal of a square is longer than its sides.
Heavy Iron
Step three: Heavy Iron. Manhole covers are heavy iron, sometimes 100 pounds or more, so they stay put under traffic. Workers use special hooks to lift them. Never try to open one.
A Closer Look
Let's take a closer look! The cover sits on top. A ladder goes down. Pipes run below. Wires may run too.
Quick Facts
Quick facts! Under many covers are ladders that lead down to pipes and wires. Round covers roll easily. Never open a manhole. Some covers have designs.
Think Like a Scientist
Now, think like a scientist! Ask a grown-up to help with the scissors. Cut a cardboard circle and a cardboard square, both bigger than a coin. In a tray lid, cut a hole slightly smaller than the circle. Can you tilt the circle through? What about the square?
Outro
Manhole covers are round because a circle has the same width in every direction, so it can never fall through its hole. They are heavy iron, so never try to open one. Science is amazing! The world is full of surprises. Keep asking big questions, and keep exploring with me! Crafty Clover can be found on Amazon Books, Google Bookstore, and Apple Books. Available for purchase or download! Bye for now!