Geometric solids

We have been studying plane figures, which have only two dimensions: length and width. Now we shall study figures with three dimensions. Figures that have three dimensions are called geometric solids or solid figures. The three dimen­sions of solid figures are length, width, and or height.

Prisms. A prism is a solid, each side of which is a polygon, and the upper base of which is parallel and congruent (exactly the same in size and shape), to the lower base: corresponding vertices of the top and bottom polygons are joined by parallel edges (Fig. 21). In a right prism, the lateral

faces (sides) are perpendicular to the bases. Right prisms include: the rectangular prism and the cube. A geometric figure which has six sides, all of which are rectangles, is called a rectangular solid or rectangular prism (Fig. 22). If the dimensions (length, width and height) of a rectangular solid are, the solid is called a cube. The faces of a cube are squares (Fig. 23).

The Right Circular Cylinder. A cylinder (Fig. 24) is a circular prism, the bases of which are equal circles that are parallel to each other. If the sides of the cylinder are perpendicular to the bases, the cylinder is called a right cylinder. The axis of a right circular cylinder is the line between the centres of the bases.

A pyramid (Fig. 25) is a solid figure formed by a polygon called the base and sides of triangles meeting at a common point called the vertex.

A cone is much like a pyramid but has a circle for a base (Fig. 26).