Clockwise
Overview
 
Circular motion can occur in two possible directions. A clockwise (typically abbreviated as CW) motion is one that proceeds in the same direction as a clock
Clock
A clock is an instrument used to indicate, keep, and co-ordinate time. The word clock is derived ultimately from the Celtic words clagan and clocca meaning "bell". A silent instrument missing such a mechanism has traditionally been known as a timepiece...

's hands: from the top to the right, then down and then to the left, and back to the top. In a mathematical sense, a circle defined parametrically in a positive Cartesian plane by the equations x = sin t and y = cos t is traced clockwise as t increases in value.
Quotations

If you've ever been late… you'll know what this film is all about!

Sharon Maiden — Laura

Category:Comedy films

Encyclopedia
Circular motion can occur in two possible directions. A clockwise (typically abbreviated as CW) motion is one that proceeds in the same direction as a clock
Clock
A clock is an instrument used to indicate, keep, and co-ordinate time. The word clock is derived ultimately from the Celtic words clagan and clocca meaning "bell". A silent instrument missing such a mechanism has traditionally been known as a timepiece...

's hands: from the top to the right, then down and then to the left, and back to the top. In a mathematical sense, a circle defined parametrically in a positive Cartesian plane by the equations x = sin t and y = cos t is traced clockwise as t increases in value. Described another way, continually turning right is clockwise motion, as viewed from above. The opposite sense of rotation
Rotation
A rotation is a circular movement of an object around a center of rotation. A three-dimensional object rotates always around an imaginary line called a rotation axis. If the axis is within the body, and passes through its center of mass the body is said to rotate upon itself, or spin. A rotation...

 or revolution
Revolution
A revolution is a fundamental change in power or organizational structures that takes place in a relatively short period of time.Aristotle described two types of political revolution:...

 is (in American English
American English
American English is a set of dialects of the English language used mostly in the United States. Approximately two-thirds of the world's native speakers of English live in the United States....

) counterclockwise (CCW), or (in British English
British English
British English, or English , is the broad term used to distinguish the forms of the English language used in the United Kingdom from forms used elsewhere...

) anticlockwise (ACW).

Origin of the term

Before clocks were commonplace, the terms "sunwise
Sunwise
In Scottish folklore, ' or Sunward was considered the “prosperous course”, turning from east to west in the direction of the sun. The opposite course was known in Scotland as widdershins , or tuathal , and would have been counterclockwise...

" and "deiseil" from the Scottish Gaelic language
Scottish Gaelic language
Scottish Gaelic is a Celtic language native to Scotland. A member of the Goidelic branch of the Celtic languages, Scottish Gaelic, like Modern Irish and Manx, developed out of Middle Irish, and thus descends ultimately from Primitive Irish....

 and from the same root as the Latin "dexter" ("right") were used for clockwise. "Widdershins
Widdershins
Widdershins means to take a course opposite the apparent motion of the sun, to go counterclockwise or lefthandwise, or to circle an object by always keeping it on the left...

" or "withershins" (from Middle Low German
Middle Low German
Middle Low German is a language that is the descendant of Old Saxon and is the ancestor of modern Low German. It served as the international lingua franca of the Hanseatic League...

 "weddersinnes", "opposite course") was used for counterclockwise.
The terms clockwise and counterclockwise can only be applied to a rotational motion once a side of the rotational plane is specified, from which the rotation is observed. For example, the daily rotation of the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

 is counterclockwise when viewed from above the North Pole
North Pole
The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is, subject to the caveats explained below, defined as the point in the northern hemisphere where the Earth's axis of rotation meets its surface...

, and clockwise when viewed from above the South Pole
South Pole
The South Pole, also known as the Geographic South Pole or Terrestrial South Pole, is one of the two points where the Earth's axis of rotation intersects its surface. It is the southernmost point on the surface of the Earth and lies on the opposite side of the Earth from the North Pole...

.

Clocks traditionally follow this sense of rotation because of the clock's predecessor: the sundial
Sundial
A sundial is a device that measures time by the position of the Sun. In common designs such as the horizontal sundial, the sun casts a shadow from its style onto a surface marked with lines indicating the hours of the day. The style is the time-telling edge of the gnomon, often a thin rod or a...

. Clocks with hands were first built in the Northern Hemisphere (see main article), and they were made to work like sundials. In order for a horizontal sundial to work (in the Northern Hemisphere), it must be placed looking southward. Then, when the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

 moves in the sky (east to south to west), the shadow cast on the opposite side of the sundial moves with the same sense of rotation (west to north to east). This is why hours were drawn in sundials in that manner, and why modern clocks have their numbers set in the same way. Note, however, that on a vertical sundial (such as those placed on the walls of buildings), the shadow moves in the opposite direction, and some clocks were constructed to mimic this. The best-known surviving example is the astronomical clock in the Münster Cathedral
Münster Cathedral
Münster Cathedral is a cathedral in the German city of Münster. It is the city's main church and one of its most important historical monuments, as well as the centre of the Diocese of Münster since that diocese's foundation in 805....

, whose hands move counterclockwise.

Occasionally, clocks whose hands revolve counterclockwise are nowadays sold as an aid to the left-handed, or as a novelty. Historically, some Jewish
Judaism
Judaism ) is the "religion, philosophy, and way of life" of the Jewish people...

 clocks were built that way, for example in some synagogue towers in Europe. This was done in accordance with the right-to-left reading direction of the Hebrew language
Hebrew language
Hebrew is a Semitic language of the Afroasiatic language family. Culturally, is it considered by Jews and other religious groups as the language of the Jewish people, though other Jewish languages had originated among diaspora Jews, and the Hebrew language is also used by non-Jewish groups, such...

.

Usage

Although considered novel there is an apparent universal consistency when counterclockwise clocks are used. As noted the shadows of vertical sundials move counterclockwise. The numbers on a counterclockwise clock now have a two-fold representation: hour and month. One can now tell time as well as know the Earth's relative seasonal position with respect to the Sun. When the planetary plane
Ecliptic
The ecliptic is the plane of the earth's orbit around the sun. In more accurate terms, it is the intersection of the celestial sphere with the ecliptic plane, which is the geometric plane containing the mean orbit of the Earth around the Sun...

 and the Earth's axis pointing or "hanging" from Polaris
Polaris
Polaris |Alpha]] Ursae Minoris, commonly North Star or Pole Star, also Lodestar) is the brightest star in the constellation Ursa Minor. It is very close to the north celestial pole, making it the current northern pole star....

 (North Star) is considered the numerical value representing each month of the year (3–March, 6–June, 9–September and 12–December, etc) indicates the Earth's relative position to the Sun. In December the Earth is at the "12 o'clock" solstice
Solstice
A solstice is an astronomical event that happens twice each year when the Sun's apparent position in the sky, as viewed from Earth, reaches its northernmost or southernmost extremes...

 position with the axis pointing away from the Sun (winter or summer depending on hemisphere). Six months later, in June, the earth is the "6 o'clock" solstice position with the Earth's axis pointing toward the Sun. In March and September respectively, 3 and 9 o'clock, the equinox position is apparent. If a clock is made "counterclockwise" it will simply rotate in the same direction as the celestial objects that dictate our calendar and seasons; the Moon around the Earth, the Earth around the Sun, and the Sun within the galaxy. Truly now a "universal" system.

Typical nuts
Nut (hardware)
A nut is a type of hardware fastener with a threaded hole. Nuts are almost always used opposite a mating bolt to fasten a stack of parts together. The two partners are kept together by a combination of their threads' friction, a slight stretch of the bolt, and compression of the parts...

, screw
Screw
A screw, or bolt, is a type of fastener characterized by a helical ridge, known as an external thread or just thread, wrapped around a cylinder. Some screw threads are designed to mate with a complementary thread, known as an internal thread, often in the form of a nut or an object that has the...

s, bolts, and bottle cap
Bottle cap
Bottle caps are a type of closure used to seal the openings of bottles of many types. They can be small circular pieces of metal, usually steel, with plastic backings, and for plastic bottles a plastic cap is used instead. A bottle cap is typically colorfully decorated with the logo of the brand...

s are tightened (moved away from the observer) clockwise and loosened (moved towards the observer) counterclockwise, in accordance with the right-hand rule
Right-hand rule
In mathematics and physics, the right-hand rule is a common mnemonic for understanding notation conventions for vectors in 3 dimensions. It was invented for use in electromagnetism by British physicist John Ambrose Fleming in the late 19th century....

.

A way of remembering this that is based on the right-hand rule is to place one's loosely-clenched right hand above the object with the thumb pointing in the direction one wants the screw, nut, bolt, or cap ultimately to move, and the curl of the fingers, from the palm to the tips, will indicate in which way one needs to turn the screw, nut, bolt or cap to achieve the desired result. Most threaded objects are susceptible to application of the above; for a countably small number of exceptions (read: "left-handed" threads, or "reverse threads"), one substitutes the left-hand rule instead.

The reason for the clockwise orientation of most screws and bolts is that supination
Supination
Supination is a position of either the forearm or foot; in the forearm when the palm faces anteriorly, or faces up . Supination in the foot occurs when a person appears "bow-legged" with their weight supported primarily on the anterior of their feet.The hand is supine in the anatomical position...

 of the arm, which is used by a right-handed person to turn a screw clockwise, is generally stronger than pronation
Pronation
In anatomy, pronation is a rotational movement of the forearm at the radioulnar joint, or of the foot at the subtalar and talocalcaneonavicular joints. For the forearm, when standing in the anatomical position, pronation will move the palm of the hand from an anterior-facing position to a...

. Also, it was wise to adopt a single standard version for most screws and bolts – in order to eliminate endless confusion.

Sometimes the opposite sense of threading is used for a special reason. A thread might need to be left-handed to prevent the prevalent stresses that are present from loosening it. For example, some older automobile
Automobile
An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...

s and trucks had right-handed lug nut
Lug nut
A lug nut is a fastener, specifically a nut, used to secure a wheel on a vehicle. Typically, lug nuts are found on automobiles, trucks , and other large vehicles utilizing rubber tires.-Design:...

s on the right side of the vehicle and left-handed lug nuts on the left side of the vehicle. As the vehicle moved forward, the lug nuts tend to tighten. For a pair of bicycle pedal
Bicycle pedal
A bicycle pedal is the part of a bicycle that the rider pushes with their foot to propel the bicycle. It provides the connection between the cyclist's foot or shoe and the crank allowing the leg to turn the bottom bracket spindle and propel the bicycle's wheels...

s, for instance, one must be reverse-threaded, or the pedal will fall off; similarly, the flyer whorl of a spinning wheel
Spinning wheel
A spinning wheel is a device for spinning thread or yarn from natural or synthetic fibers. Spinning wheels appeared in Asia, probably in the 11th century, and very gradually replaced hand spinning with spindle and distaff...

 uses a left-hand thread to keep from loosening in normal use. A turnbuckle
Turnbuckle
A turnbuckle, stretching screw or bottlescrew is a device for adjusting the tension or length of ropes, cables, tie rods, and other tensioning systems. It normally consists of two threaded eyelets, one screwed into each end of a small metal frame, one with a left-hand thread and the other with a...

 has right-handed threads on one end and left-handed threads on the other end. Some gas fittings are left-handed to prevent disastrous misconnections. For example, oxygen fittings are right-handed, but acetylene
Acetylene
Acetylene is the chemical compound with the formula C2H2. It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in pure form and thus is usually handled as a solution.As an alkyne, acetylene is unsaturated because...

 and other flammable gases use left-handed fittings.

In trigonometry
Trigonometry
Trigonometry is a branch of mathematics that studies triangles and the relationships between their sides and the angles between these sides. Trigonometry defines the trigonometric functions, which describe those relationships and have applicability to cyclical phenomena, such as waves...

, and in mathematics
Mathematics
Mathematics is the study of quantity, space, structure, and change. Mathematicians seek out patterns and formulate new conjectures. Mathematicians resolve the truth or falsity of conjectures by mathematical proofs, which are arguments sufficient to convince other mathematicians of their validity...

 in general, plane angle
Angle
In geometry, an angle is the figure formed by two rays sharing a common endpoint, called the vertex of the angle.Angles are usually presumed to be in a Euclidean plane with the circle taken for standard with regard to direction. In fact, an angle is frequently viewed as a measure of an circular arc...

s are conventionally measured counterclockwise, starting with 0° or 0 radian
Radian
Radian is the ratio between the length of an arc and its radius. The radian is the standard unit of angular measure, used in many areas of mathematics. The unit was formerly a SI supplementary unit, but this category was abolished in 1995 and the radian is now considered a SI derived unit...

s pointed directly to the right (or east). In navigation
Navigation
Navigation is the process of monitoring and controlling the movement of a craft or vehicle from one place to another. It is also the term of art used for the specialized knowledge used by navigators to perform navigation tasks...

, compass
Compass
A compass is a navigational instrument that shows directions in a frame of reference that is stationary relative to the surface of the earth. The frame of reference defines the four cardinal directions – north, south, east, and west. Intermediate directions are also defined...

 headings increase in a clockwise direction around the compass face, starting with 0° at the top of the compass (the northerly direction).

In humans

Most left-handed humans prefer to draw circles clockwise and circulate in buildings clockwise, and most right-handed people prefer to draw circles counterclockwise and circulate in buildings counterclockwise. It is believed that this can be attributed to dominant brain hemispheres.

See also

  • Handedness
    Handedness
    Handedness is a human attribute defined by unequal distribution of fine motor skills between the left and right hands. An individual who is more dexterous with the right hand is called right-handed and one who is more skilled with the left is said to be left-handed...

  • Chirality (physics)
    Chirality (physics)
    A chiral phenomenon is one that is not identical to its mirror image . The spin of a particle may be used to define a handedness for that particle. A symmetry transformation between the two is called parity...

    , Chirality (chemistry)
    Chirality (chemistry)
    A chiral molecule is a type of molecule that lacks an internal plane of symmetry and thus has a non-superimposable mirror image. The feature that is most often the cause of chirality in molecules is the presence of an asymmetric carbon atom....

  • Inner/Outer orientation
  • Optical isomerism
  • Retrograde motion
    Retrograde motion
    Retrograde motion is motion in the direction opposite to the movement of something else, and is the contrary of direct or prograde motion. This motion can be the orbit of one body about another body or about some other point, or the rotation of a single body about its axis, or other phenomena such...

  • Relative direction
    Relative direction
    The most common relative directions are left, right, forward, backward, up, and down. No absolute direction corresponds to any of the relative directions. This is a consequence of the translational invariance of the laws of physics: nature, loosely speaking, behaves the same no matter what...

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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