The term ""chord"" is applied in several sciences. In geometry it is a straight line piece which connects two points of a curve, usually a circle or an ellipse. In zoology this term call longitudinal tyazh, a backbone prototype. At last, in sociology the chord represents type of the organization, the most primitive of all existing.
To receive a geometrical chord, draw a circle. Designate on it two points and carry out through them a secant. The piece which is between points of intersection of this line and a circle will also be a chord. Consider properties of a chord. Halve it and carry out a perpendicular from this point. It will pass also through the center of a circle. If to arrive on the contrary and to carry out the radius perpendicular to a chord from the center, then it will divide it into 2 equal parts.
Carry out the second chord equal on length which is already available and parallel to it. Connect points of intersection of both chords to its center. You receive 2 triangles which are equal among themselves on three parties (pieces from the center to lines of crossing of chords with a circle represent radiuses, and chords are equal among themselves under the terms of a task). Respectively, heights which are carried out to the equal parties are equal among themselves too. That is these chords are removed from the center of a circle on equal distances. Other property of equal and parallel chords also follows from equality of triangles - the arches concluded between them are equal among themselves.
Not the parallel chords crossing the same circle have special characteristics also. If they are crossed, then are divided into pieces, and their ratio can be calculated. The work of pieces into which one of chords is divided in a point of intersection is equal to the work of pieces another. At first sight can seem that mathematical and zoological terms are among themselves not connected. But it not absolutely so. This word in translation from Greek is meant by ""string"". In geometry it is the string which is pulling together a segment, and in zoology - a back string, that is a nesegmentiovanny skeletal axis. The organisms having such axis are called chordates. Chordates - type of vtorichnopolostny animals, it includes several subtypes. All animals of this type have a spinal tube and branchiate cracks. At the majority of the organisms relating to chordates, the back string is present only at the beginning of development. Then instead of it the backbone appears. However there are also lowest chordates at whom such skeletal axis remains for the rest of life. Lancelets, an oykoplevra treat such animals, for example. In biology and medicine also other chords meet. A chord it is accepted to call any threadlike structure. There are tendinous chords, nervous fibers. embryo chord. The last just is also an example of a back string which at the person disappears in process of development of a germ. This term is rather widely applied in the equipment. As well as in geometry, it designates the straight line connecting two points of a curve. For example, in aircraft there is a term ""the chord covered"" the Average aerodynamic chord is one of the most important parameters of the aircraft.