# Why do so many children's book confuse discs with circles? [duplicate]

The difference between a disc (disk) and a circle is crystal clear to me:

However, in many children's books, a disc is usually called a circle:

Why do many children's book confuse discs with circles? Should we teach children the difference between a disc and a circle?

• The underlying reason could probably be the dual meaning of circle in everyday English. Thus, confusion wouldn't be the best word to describe the situation. Mar 25, 2022 at 15:41
• I see an annulus and a disk. Mar 25, 2022 at 18:00
• This isn't "confusion", this is (appropriately) using one of the the ordinary English meanings of the word "circle" rather than the technical mathematical definition. Mar 25, 2022 at 21:36
• Are you perhaps implying that the surface area of a circle is zero?
– knl
Mar 25, 2022 at 23:18
• @JoelReyesNoche, you are right. The formula $\pi r^2$ gives the area of a disc, while the area of every circle is zero. Mar 27, 2022 at 1:46