Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. A surface of revolution is a surface in Euclidean space created by rotating a curve (the generatrix) around a straight line in its plane (the axis)Examples of surfaces generated by a straight line are cylindrical and conical surfaces when the line is coplanar with the axis, as well as hyperboloids of one sheet when the line is skew to the axis. A circle that is rotated about a diameter generates a sphere and if the circle is rotated about a coplanar axis other than the diameter it generates a torus.