So no curved surfaces: cones, spheres and cylinders are not polyhedrons.
Note: the plural of polyhedron is either polyhedrons or polyhedra
Explore 100s of Animated Polyhedron Models.
You can also see some Images of Polyhedra if you want.
When we count the number of faces (the flat surfaces), vertices (corner points), and edges of a polyhedron we discover an interesting thing:
The number of faces
plus the number of vertices
minus the number of edges equals 2
This can be written neatly as a little equation:
It is known as Euler's Formula (or the "Polyhedral Formula") and is very useful to make sure we have counted correctly!
A cube has:
F + V − E = 6 + 8 − 12 = 2
This prism has:
F + V − E = 5 + 6 − 9 = 2
But there are cases where it does not work! Read Euler's Formula for more.
A diagonal is a straight line inside a shape that goes from one corner to another (but not an edge).
A polyhedron can have lots of diagonals. Can you think of one without diagonals?