Relative direction
Encyclopedia
The most common relative directions
are left, right, forward(s), backward(s), 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 direction one moves. As demonstrated by the Michelson-Morley null result
, there is no absolute inertial frame of reference
. There are definite relationships between the relative directions, however. Left and right, forward and backward, and up and down are three pairs of complementary directions, each pair orthogonal to both of the others. Relative directions are also known as egocentric coordinates.
for instance, in their language
have no words denoting the egocentric directions, but instead exclusively refer to cardinal directions, even when describing small-scale spaces. For instance, if they want someone to move over on the car seat to make room, they would say "move a bit to the east." To tell someone where exactly they left something in their house, they would say, "I left it on the southern edge of the western table." Or they would warn a person to "look out for that big ant just north of your foot." Other peoples "from Polynesia to Mexico and from Namibia to Bali" similarly have predominantly "geographic languages". American Sign Language
makes heavy use of geographical direction through absolute orientation. When speaking Mongolian
, speakers will typically use the words for "front", "back", "left", and "right" to mean "south", "north", "east", and "west", respectively.
, aft
, port, and starboard
are nautical terms that convey an impersonal relative direction in the context of the moving frame of persons aboard a ship.
up, they will have moved negative one meter down. Furthermore, they will not have moved left or right at all, nor forward or backward. One must mind the geometry
of the environment
when using relative direction to express motion
, however. For example, if someone continues walking forward until they have almost circumnavigated the Earth, they will expend much effort only to move backward slightly. This is because Earth is (near-)spherical.
The right-hand rule
is one common way to relate the three principal directions. For many years a fundamental question
in physics was whether a left-hand rule would be equivalent. Many natural structures
, including human bodies, follow a certain handedness
, but it was widely assumed that nature did not distinguish the two possibilities. This changed with the discovery of parity violations in particle physics
. If a sample of cobalt-60
atoms is magnetize
d so that they spin counterclockwise around some axis
, the beta radiation resulting from their nuclear decay will be preferentially directed opposite that axis. Since counter-clockwise may be defined in terms of up, forward, and right, this experiment unambiguously differentiates left from right using only natural elements: If they were reversed, or the atoms spun clockwise
, the radiation would follow the spin axis instead of being opposite to it.
, acculturation
, education
, and direct reference. One common definition of up and down uses gravity and the planet Earth
as a frame of reference. Since there is a very noticeable force of gravity acting between the Earth and any other nearby object, down is defined as that direction which an object moves in reference to the Earth when the object is allowed to fall freely
. Up is then defined as the opposite direction of down. Another common definition uses a human body, standing upright, as a frame of reference. In that case, up is defined as the direction from feet to head, perpendicular to the surface of the Earth. In most cases, up is a directionally oriented position generally opposite to that of the pull of gravity.
Forward and backward may be defined by referring to an object or person's motion
. Forward is defined as the direction in which the object is moving. Backward is then defined as the opposite direction to forward. Alternatively, 'forward' may be the direction pointed by the observer's nose
, defining 'backward' as the direction from the nose to the sagittal border
in the observer's skull
. With respect to a ship 'forward' would indicate the relative position of any object lying in the direction the ship is pointing. Objects on ships can be named from their location, for example 'Forward Fire Pump' or 'Aft Fire Pump'.
The terms left and right are derived from the fact that 70-90% of the human population use the right hand for writing
and other manual tasks. Through cognate of the word right in the meaning "correct" or "good", the side with the hand most used was defined as the right side. The word "left" comes from the Old English
lyft, meaning weak. This dichotomy
can also be seen in the words "dextrous" and "sinister," from the Latin
words for right and left.
Given significant distance from the equator
, one can figure which hand is which using a clock
, a compass
, and the sun
. Facing the sun, in the northern hemisphere, before noon, the compass points to the left hand. After noon, it points to the right. The opposite is true of the southern hemisphere. In most people, the heart
is to the left of the body's center line and the liver
is to the right.
) it affects about 15% of the population. These people can usually normally perform daily activities such as driving according to signs and navigating according to a map, but will often take a wrong turn when told to turn left or right and may have difficulties performing actions that require precise understanding of directional commands, such as ballroom dancing.
Direction (geometry, geography)
Direction is the information contained in the relative position of one point with respect to another point without the distance information. Directions may be either relative to some indicated reference , or absolute according to some previously agreed upon frame of reference Direction is the...
are left, right, forward(s), backward(s), up, and down. No absolute
Absolute value
In mathematics, the absolute value |a| of a real number a is the numerical value of a without regard to its sign. So, for example, the absolute value of 3 is 3, and the absolute value of -3 is also 3...
direction corresponds to any of the relative directions. This is a consequence of the translational invariance
Translational symmetry
In geometry, a translation "slides" an object by a a: Ta = p + a.In physics and mathematics, continuous translational symmetry is the invariance of a system of equations under any translation...
of the laws of physics
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
: nature, loosely speaking, behaves the same no matter what direction one moves. As demonstrated by the Michelson-Morley null result
Michelson-Morley experiment
The Michelson–Morley experiment was performed in 1887 by Albert Michelson and Edward Morley at what is now Case Western Reserve University in Cleveland, Ohio. Its results are generally considered to be the first strong evidence against the theory of a luminiferous ether and in favor of special...
, there is no absolute inertial frame of reference
Inertial frame of reference
In physics, an inertial frame of reference is a frame of reference that describes time homogeneously and space homogeneously, isotropically, and in a time-independent manner.All inertial frames are in a state of constant, rectilinear motion with respect to one another; they are not...
. There are definite relationships between the relative directions, however. Left and right, forward and backward, and up and down are three pairs of complementary directions, each pair orthogonal to both of the others. Relative directions are also known as egocentric coordinates.
Cultures not using relative directions
Many human cultures use relative directions for reference. However, some do not. The Australian Aboriginal people the Guugu YimithirrGuugu Yimithirr people
The Guugu Yimithirr are an Australian Aboriginal tribe of Far North Queensland, many of whom today live at Hopevale , which is the administrative centre of Hopevale Shire. It is about 46 km from Cooktown by road. It is also the name of their language...
for instance, in their language
Guugu Yimithirr language
Guugu Yimithirr is an Australian Aboriginal language, the traditional language of the Guugu Yimithirr people of Far North Queensland. Most of the speakers today live at the community of Hopevale, about 46 km from Cooktown...
have no words denoting the egocentric directions, but instead exclusively refer to cardinal directions, even when describing small-scale spaces. For instance, if they want someone to move over on the car seat to make room, they would say "move a bit to the east." To tell someone where exactly they left something in their house, they would say, "I left it on the southern edge of the western table." Or they would warn a person to "look out for that big ant just north of your foot." Other peoples "from Polynesia to Mexico and from Namibia to Bali" similarly have predominantly "geographic languages". American Sign Language
American Sign Language
American Sign Language, or ASL, for a time also called Ameslan, is the dominant sign language of Deaf Americans, including deaf communities in the United States, in the English-speaking parts of Canada, and in some regions of Mexico...
makes heavy use of geographical direction through absolute orientation. When speaking Mongolian
Mongolian language
The Mongolian language is the official language of Mongolia and the best-known member of the Mongolic language family. The number of speakers across all its dialects may be 5.2 million, including the vast majority of the residents of Mongolia and many of the Mongolian residents of the Inner...
, speakers will typically use the words for "front", "back", "left", and "right" to mean "south", "north", "east", and "west", respectively.
Nautical terminology
BowBow (ship)
The bow is a nautical term that refers to the forward part of the hull of a ship or boat, the point that is most forward when the vessel is underway. Both of the adjectives fore and forward mean towards the bow...
, aft
Aft
Aft, in naval terminology, is an adjective or adverb meaning, towards the stern of the ship, when the frame of reference is within the ship. Example: "Able Seaman Smith; lay aft!". Or; "What's happening aft?"...
, port, and starboard
Port and starboard
Port and starboard are nautical terms which refer to the left and right sides, respectively, of a ship or aircraft as perceived by a person on board facing the bow . At night, the port side of a vessel is indicated with a red navigation light and the starboard side with a green one.The starboard...
are nautical terms that convey an impersonal relative direction in the context of the moving frame of persons aboard a ship.
Geometry of natural environment
If someone climbs a rope one meter1 E0 m
To help compare different orders of magnitude this page lists lengths between one metre and ten metres.Distances shorter than 1 m-Conversions:1 metre is:* 10 decimetres* 100 centimetres* 1000 millimetres* 39.37 inches* 3.28 feet...
up, they will have moved negative one meter down. Furthermore, they will not have moved left or right at all, nor forward or backward. One must mind the geometry
Geometry
Geometry arose as the field of knowledge dealing with spatial relationships. Geometry was one of the two fields of pre-modern mathematics, the other being the study of numbers ....
of the environment
Natural environment
The natural environment encompasses all living and non-living things occurring naturally on Earth or some region thereof. It is an environment that encompasses the interaction of all living species....
when using relative direction to express motion
Motion (physics)
In physics, motion is a change in position of an object with respect to time. Change in action is the result of an unbalanced force. Motion is typically described in terms of velocity, acceleration, displacement and time . An object's velocity cannot change unless it is acted upon by a force, as...
, however. For example, if someone continues walking forward until they have almost circumnavigated the Earth, they will expend much effort only to move backward slightly. This is because Earth is (near-)spherical.
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....
is one common way to relate the three principal directions. For many years a fundamental question
Parity (physics)
In physics, a parity transformation is the flip in the sign of one spatial coordinate. In three dimensions, it is also commonly described by the simultaneous flip in the sign of all three spatial coordinates:...
in physics was whether a left-hand rule would be equivalent. Many natural structures
Nature
Nature, in the broadest sense, is equivalent to the natural world, physical world, or material world. "Nature" refers to the phenomena of the physical world, and also to life in general...
, including human bodies, follow a certain 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...
, but it was widely assumed that nature did not distinguish the two possibilities. This changed with the discovery of parity violations in particle physics
Particle physics
Particle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...
. If a sample of cobalt-60
Cobalt
Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal....
atoms is magnetize
Magnetism
Magnetism is a property of materials that respond at an atomic or subatomic level to an applied magnetic field. Ferromagnetism is the strongest and most familiar type of magnetism. It is responsible for the behavior of permanent magnets, which produce their own persistent magnetic fields, as well...
d so that they spin counterclockwise around some axis
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...
, the beta radiation resulting from their nuclear decay will be preferentially directed opposite that axis. Since counter-clockwise may be defined in terms of up, forward, and right, this experiment unambiguously differentiates left from right using only natural elements: If they were reversed, or the atoms spun clockwise
Clockwise
Circular motion can occur in two possible directions. A clockwise motion is one that proceeds in the same direction as a clock's hands: from the top to the right, then down and then to the left, and back to the top...
, the radiation would follow the spin axis instead of being opposite to it.
Tradition and acculturation
Since definitions of left and right based on the geometry of the natural environment are unwieldy, in practice, the meaning of relative direction words is conveyed through traditionTradition
A tradition is a ritual, belief or object passed down within a society, still maintained in the present, with origins in the past. Common examples include holidays or impractical but socially meaningful clothes , but the idea has also been applied to social norms such as greetings...
, acculturation
Acculturation
Acculturation explains the process of cultural and psychological change that results following meeting between cultures. The effects of acculturation can be seen at multiple levels in both interacting cultures. At the group level, acculturation often results in changes to culture, customs, and...
, education
Education
Education in its broadest, general sense is the means through which the aims and habits of a group of people lives on from one generation to the next. Generally, it occurs through any experience that has a formative effect on the way one thinks, feels, or acts...
, and direct reference. One common definition of up and down uses gravity and the planet 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...
as a frame of reference. Since there is a very noticeable force of gravity acting between the Earth and any other nearby object, down is defined as that direction which an object moves in reference to the Earth when the object is allowed to fall freely
Free-fall
Free fall is any motion of a body where gravity is the only force acting upon it, at least initially. These conditions produce an inertial trajectory so long as gravity remains the only force. Since this definition does not specify velocity, it also applies to objects initially moving upward...
. Up is then defined as the opposite direction of down. Another common definition uses a human body, standing upright, as a frame of reference. In that case, up is defined as the direction from feet to head, perpendicular to the surface of the Earth. In most cases, up is a directionally oriented position generally opposite to that of the pull of gravity.
Forward and backward may be defined by referring to an object or person's motion
Motion (physics)
In physics, motion is a change in position of an object with respect to time. Change in action is the result of an unbalanced force. Motion is typically described in terms of velocity, acceleration, displacement and time . An object's velocity cannot change unless it is acted upon by a force, as...
. Forward is defined as the direction in which the object is moving. Backward is then defined as the opposite direction to forward. Alternatively, 'forward' may be the direction pointed by the observer's nose
Human nose
The visible part of the human nose is the protruding part of the face that bears the nostrils. The shape of the nose is determined by the ethmoid bone and the nasal septum, which consists mostly of cartilage and which separates the nostrils...
, defining 'backward' as the direction from the nose to the sagittal border
Parietal bone
The parietal bones are bones in the human skull which, when joined together, form the sides and roof of the cranium. Each bone is roughly quadrilateral in form, and has two surfaces, four borders, and four angles. It is named from the Latin pariet-, wall....
in the observer's skull
Human skull
The human skull is a bony structure, skeleton, that is in the human head and which supports the structures of the face and forms a cavity for the brain.In humans, the adult skull is normally made up of 22 bones...
. With respect to a ship 'forward' would indicate the relative position of any object lying in the direction the ship is pointing. Objects on ships can be named from their location, for example 'Forward Fire Pump' or 'Aft Fire Pump'.
The terms left and right are derived from the fact that 70-90% of the human population use the right hand for writing
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...
and other manual tasks. Through cognate of the word right in the meaning "correct" or "good", the side with the hand most used was defined as the right side. The word "left" comes from the Old English
Old English language
Old English or Anglo-Saxon is an early form of the English language that was spoken and written by the Anglo-Saxons and their descendants in parts of what are now England and southeastern Scotland between at least the mid-5th century and the mid-12th century...
lyft, meaning weak. This dichotomy
Dichotomy
A dichotomy is any splitting of a whole into exactly two non-overlapping parts, meaning it is a procedure in which a whole is divided into two parts...
can also be seen in the words "dextrous" and "sinister," from the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
words for right and left.
Given significant distance from the equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....
, one can figure which hand is which using 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...
, a 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...
, and 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...
. Facing the sun, in the northern hemisphere, before noon, the compass points to the left hand. After noon, it points to the right. The opposite is true of the southern hemisphere. In most people, the heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
is to the left of the body's center line and the liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
is to the right.
Left-right confusion
Left-right confusion is the difficulty some people have in distinguishing the difference between the directions left and right. According to research by John R. Clarke (Drexel UniversityDrexel University
Drexel University is a private research university with the main campus located in Philadelphia, Pennsylvania, USA. It was founded in 1891 by Anthony J. Drexel, a noted financier and philanthropist. Drexel offers 70 full-time undergraduate programs and accelerated degrees...
) it affects about 15% of the population. These people can usually normally perform daily activities such as driving according to signs and navigating according to a map, but will often take a wrong turn when told to turn left or right and may have difficulties performing actions that require precise understanding of directional commands, such as ballroom dancing.
See also
- Anatomical terms of locationAnatomical terms of locationStandard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
- Cardinal directionCardinal directionThe four cardinal directions or cardinal points are the directions of north, east, south, and west, commonly denoted by their initials: N, E, S, W. East and west are at right angles to north and south, with east being in the direction of rotation and west being directly opposite. Intermediate...
- Cerebral hemisphereCerebral hemisphereA cerebral hemisphere is one of the two regions of the eutherian brain that are delineated by the median plane, . The brain can thus be described as being divided into left and right cerebral hemispheres. Each of these hemispheres has an outer layer of grey matter called the cerebral cortex that is...
- Clock positionClock positionClock position is a way of communicating the relative direction of an object using the analogy of a 12-hour clock. One imagines a clock face lying either upright or flat in front of oneself, and identifies the twelve hour markings with the directions in which they point.Using this analogy, 12...
- List of international common standards
- Port and starboardPort and starboardPort and starboard are nautical terms which refer to the left and right sides, respectively, of a ship or aircraft as perceived by a person on board facing the bow . At night, the port side of a vessel is indicated with a red navigation light and the starboard side with a green one.The starboard...
- RotationRotationA 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...
- Windward and leewardWindward and leewardWindward is the direction upwind from the point of reference. Leeward is the direction downwind from the point of reference. The side of a ship that is towards the leeward is its lee side. If the vessel is heeling under the pressure of the wind, this will be the "lower side"...