What is a Reuleaux polygon?

Have you ever noticed that manhole covers on the street are almost always round? It turns out, this isn't just a random design choice—it is a life-saving piece of maths! If a manhole cover were square, it could accidentally tilt and slip diagonally right down the hole, crashing into the dark sewer below! But a circle is a special shape with "constant width." That means no matter which way you turn it, measure it, or tip it, it is exactly the same distance across. It can never fall in! But hold onto your hats, because circles aren't the only shapes with this math magic. In the 1870s, a German engineer named Franz Reuleaux discovered weird, bulging, curved-sided shapes that also have constant width! Even though they have corners, they can roll completely flat! Join Mira and Finn as they uncover the incredible secrets of Reuleaux polygons. You will even learn how the bumpy, seven-sided British fifty pence coin tricks vending machines into thinking it is perfectly round! Get ready to look at the streets and your piggy bank in a totally new way!