Various Geometrical Solids

We encounter many different three-dimensional objects in our daily lives. These objects can be divided into two main categories based on their surface characteristics. Some have entirely flat surfaces, while others have rounded or curved surfaces.

Think of everyday items like books, boxes, and dice - these have completely flat faces. On the other hand, objects like basketballs and pipes have curved surfaces. This key difference allows us to sort 3D shapes into two groups:

Let's look at some examples of the first group. Notice how these shapes have no curves at all - they're made up entirely of flat surfaces that meet at edges. We call these shapes polyhedra (or a single one is called a polyhedron).

In the previous sections, we studied the properties of circles on a flat surface. But our world is actually three-dimensional, so lets have a look at some 3D solids that are based on circles:

Now, look at the other group. These shapes feature curved surfaces. They don't have only flat faces meeting at straight edges. We classify these as non-polyhedra.

This distinction between flat-faced and curved-surface objects gives us a simple way to categorize all the three-dimensional shapes we see around us.