Definition of surfaces of the solids or 3-D figures:
When we look at the faces of these figures or shapes, we find that some are flat and some are curved. These faces are not only seen but can also be touched. These are called the surfaces of the solids or 3-D figures.
There are two types of surfaces: (i) Plane surfaces and (ii) Curved surface
(i) Plane surfaces:
Flat surfaces are called plane surfaces. The objects having plane surfaces are called plane objects.
The surfaces of book, match box, almirah, table, etc., are the examples of plane surfaces.
(ii) Curved surface:
The surfaces which are not flat, are called curved surface.
The surface of a ball, or an apple, or an orange is curved or is a spherical surface.
Spherical surfaces are formed by only one surface.
There are some objects which have both plane and curved types of surfaces. Drum and clock are such objects having both types of surfaces.