Овал: форма, определение и разновидности

Shape

An oval (from Latin ovum 'egg') is a closed curve in a plane which resembles the outline of an egg. The term is not very specific, but in some areas (projective geometry, technical drawing, etc.) it is given a more precise definition, which may include either one or two axes of symmetry of an ellipse. In common English, the term is used in a broader sense: any shape which reminds one of an egg. The three dimensional version of an oval is called an ovoid.

The shape of an egg is approximated by the "long" half of a prolate spheroid, joined to a "short" half of a roughly spherical ellipsoid, or even a slightly oblate spheroid. These are joined at the equator and share a principal axis of rotational symmetry, as illustrated above. Although the term egg shaped usually implies a lack of reflection symmetry across the equatorial plane, it may also refer to true prolate ellipsoids. It can also be used to describe the 2 dimensional figure that, if revolved around its major axis, produces the 3 dimensional surface.

In technical drawing, an oval is a figure that is constructed from two pairs of arcs, with two different radii (see image on the right). The arcs are joined at a point in which lines tangential to both joining arcs lie on the same line, thus making the joint smooth. Any point of an oval belongs to an arc with a constant radius (shorter or longer), but in an ellipse, the radius is continuously changing.

In common speech, "oval" means a shape rather like an egg or an ellipse, which may be two dimensional or three dimensional. It also often refers to a figure that resembles two semicircles joined by a rectangle, like a cricket infield, speed skating rink or an athletics track. However, this is most correctly called a stadium. The term "ellipse" is often used interchangeably with oval, despite not being a precise synonym. The term "oblong" is often used incorrectly to describe an elongated oval or 'stadium' shape. However, in geometry, an oblong is a rectangle with unequal adjacent sides (i. e., not a square).