Illustration of a simple three-axis gimbal set; the center ring can be vertically fixed
A gimbal is a pivoted support that permits rotation of an object about an axis. A set of three gimbals, one mounted on the other with orthogonal
pivot axes, may be used to allow an object mounted on the innermost
gimbal to remain independent of the rotation of its support (e.g.
vertical in the first animation). For example, on a ship, the gyroscopes, shipboard compasses, stoves, and even drink holders typically use gimbals to keep them upright with respect to the horizon despite the ship's pitching and rolling.
The gimbal suspension used for mounting compasses and the like is sometimes called a Cardan suspension after Italian mathematician and physicist Gerolamo Cardano
(1501–1576) who described it in detail. However, Cardano did not
invent the gimbal, nor did he claim to. The device has been known since
antiquity, first described in the 3rd c. BC by Philo of Byzantium, although some modern authors support the view that it may not have a single identifiable inventor.
The gimbal was first described by the Greek inventor Philo of Byzantium (280–220 BC).Philo described an eight-sided ink pot with an opening on each side,
which can be turned so that while any face is on top, a pen can be
dipped and inked — yet the ink never runs out through the holes of the
other sides. This was done by the suspension of the inkwell at the
center, which was mounted on a series of concentric metal rings so that
it remained stationary no matter which way the pot is turned.
In Ancient China, the Han dynasty (202 BC – 220 AD) inventor and mechanical engineer Ding Huan created a gimbal incense burner around 180 AD. There is a hint in the writing of the earlier Sima Xiangru (179–117 BC) that the gimbal existed in China since the 2nd century BC. There is mention during the Liang dynasty (502–557) that gimbals were used for hinges of doors and windows, while an artisan once presented a portable warming stove to Empress Wu Zetian (r. 690–705) which employed gimbals. Extant specimens of Chinese gimbals used for incense burners date to the early Tang dynasty (618–907), and were part of the silver-smithing tradition in China.
The authenticity of Philo's description of a cardan suspension
has been doubted by some authors on the ground that the part of Philo's Pneumatica which describes the use of the gimbal survived only in an Arabic translation of the early 9th century. Thus, as late as 1965, the sinologistJoseph Needham suspected Arab interpolation. However, Carra de Vaux, author of the French translation which still provides the basis for modern scholars, regards the Pneumatics as essentially genuine.
The historian of technology George Sarton (1959) also asserts that it
is safe to assume the Arabic version is a faithful copying of Philo's
original, and credits Philon explicitly with the invention. So does his colleague Michael Lewis (2001).
In fact, research by the latter scholar (1997) demonstrates that the
Arab copy contains sequences of Greek letters which fell out of use
after the 1st century, thereby strengthening the case that it is a
faithful copy of the Hellenistic original, a view recently also shared by the classicist Andrew Wilson (2002).
The ancient Roman author Athenaeus Mechanicus, writing during the reign of Augustus (30 BC–14 AD), described the military use of a gimbal-like mechanism, calling it "little ape" (pithêkion).
When preparing to attack coastal towns from the sea-side, military
engineers used to yoke merchant-ships together to take the siege
machines up to the walls. But to prevent the shipborne machinery from
rolling around the deck in heavy seas, Athenaeus advises that "you must
fix the pithêkion on the platform attached to the merchant-ships in the middle, so that the machine stays upright in any angle".
After antiquity, gimbals remained widely known in the Near East. In the Latin West, reference to the device appeared again in the 9th century recipe book called the Little Key of Painting' (mappae clavicula). The French inventor Villard de Honnecourt depicts a set of gimbals in his sketchbook (see right). In the early modern period, dry compasses were suspended in gimbals.
Applications
In a set of three gimbals mounted together, each offers a degree of freedom: roll, pitch and yaw
Inertial navigation
In inertial navigation, as applied to ships and submarines, a minimum of three gimbals are needed to allow an inertial navigation system
(stable table) to remain fixed in inertial space, compensating for
changes in the ship's yaw, pitch, and roll. In this application, the inertial measurement unit (IMU) is equipped with three orthogonally
mounted gyros to sense rotation about all axes in three-dimensional
space. The gyro outputs are kept to a null through drive motors on each
gimbal axis, to maintain the orientation of the IMU. To accomplish this,
the gyro error signals are passed through "resolvers"
mounted on the three gimbals, roll, pitch and yaw. These resolvers
perform an automatic matrix transformation according to each gimbal
angle, so that the required torques are delivered to the appropriate
gimbal axis. The yaw torques must be resolved by roll and pitch
transformations. The gimbal angle is never measured.
Similar sensing platforms are used on aircraft.
In inertial navigation systems, gimbal lock
may occur when vehicle rotation causes two of the three gimbal rings to
align with their pivot axes in a single plane. When this occurs, it is
no longer possible to maintain the sensing platform's orientation.
In spacecraft propulsion, rocket engines are generally mounted on a pair of gimbals to allow a single engine to vector thrust
about both the pitch and yaw axes; or sometimes just one axis is
provided per engine. To control roll, twin engines with differential pitch or yaw control signals are used to provide torque about the vehicle's roll axis.
Photography and imaging
Man using gimbal for smartphoneA Baker-Nunn satellite-tracking camera on an altitude-altitude-azimuth mount
Gimbals are also used to mount everything from small camera lenses to large photographic telescopes.
In portable photography equipment, single-axis gimbal heads are
used in order to allow a balanced movement for camera and lenses. This proves useful in wildlife photography as well as in any other case where very long and heavy telephoto lenses are adopted: a gimbal head rotates a lens around its center of gravity, thus allowing for easy and smooth manipulation while tracking moving subjects.
Gimbal systems are also used in scientific optics equipment. For
example, they are used to rotate a material sample along an axis to
study their angular dependence of optical properties.
Film and video
NEWTON S2 gimbal for remote control and 3-axis stabilization of a RED camera, Teradek lens motors and Angénieux lens
Handheld 3-axis gimbals are used in stabilization systems
designed to give the camera operator the independence of handheld
shooting without camera vibration or shake. There are two versions of
such stabilization systems: mechanical and motorized.
Mechanical gimbals have the sled, which includes the top stage where the camera is attached, the post
which in most models can be extended, with the monitor and batteries at
the bottom to counterbalance the camera weight. This is how the
Steadicam stays upright, by simply making the bottom slightly heavier
than the top, pivoting at the gimbal. This leaves the center of gravity
of the whole rig, however heavy it may be, exactly at the operator's
fingertip, allowing deft and finite control of the whole system with the
lightest of touches on the gimbal.
Powered by three brushless motors,
motorized gimbals have the ability to keep the camera level on all axes
as the camera operator moves the camera. An inertial measurement unit
(IMU) responds to movement and utilizes its three separate motors to
stabilize the camera. With the guidance of algorithms, the stabilizer is
able to notice the difference between deliberate movement such as pans
and tracking shots from unwanted shake. This allows the camera to seem
as if it is floating through the air, an effect achieved by a Steadicam in the past. Gimbals can be mounted to cars and other vehicles such as drones,
where vibrations or other unexpected movements would make tripods or
other camera mounts unacceptable. An example which is popular in the
live TV broadcast industry, is the Newton 3-axis camera gimbal.
Marine chronometers
The rate of a mechanical marine chronometer
is sensitive to its orientation. Because of this, chronometers were
normally mounted on gimbals, in order to isolate them from the rocking
motions of a ship at sea.
Gimbal with 3 axes of rotation. When two gimbals rotate around the same axis, the system loses one degree of freedom.
Gimbal lock is the loss of one degree of freedom in a
three-dimensional, three-gimbal mechanism that occurs when the axes of
two of the three gimbals are driven into a parallel configuration,
"locking" the system into rotation in a degenerate two-dimensional
space.
The word lock is misleading: no gimbal is restrained. All three
gimbals can still rotate freely about their respective axes of
suspension. Nevertheless, because of the parallel orientation of two of
the gimbals' axes there is no gimbal available to accommodate rotation
about one axis.
Stenciled hands at the Cueva de las Manos in Argentina. Left hands make up over 90% of the artwork, demonstrating the prevalence of right-handedness. A student writes with their left hand.
In human biology, handedness is an individual's preferential use of one hand, known as the dominant hand, due to it being stronger, faster or more dextrous. The other hand, comparatively often the weaker, less dextrous or simply less subjectively preferred, is called the non-dominant hand.
In a study from 1975 on 7,688 children in US grades 1–6, left handers
comprised 9.6% of the sample, with 10.5% of male children and 8.7% of
female children being left-handed. Overall, around 90% of people are right-handed.
Handedness is often defined by one's writing hand, as it is fairly
common for people to prefer to do a particular task with a particular
hand. There are people with true ambidexterity (equal preference of either hand), but it is rare—most people prefer using one hand for most purposes.
Most of the current research suggests that left-handedness has an epigenetic marker—a combination of genetics, biology and the environment.
Because the vast majority of the population is right-handed, many
devices are designed for use by right-handed people, making their use
by left-handed people more difficult.
In many countries, left-handed people are or were required to write
with their right hands. However, left-handed people have an advantage in
sports
that involve aiming at a target in an area of an opponent's control, as
their opponents are more accustomed to the right-handed majority. As a
result, they are over-represented in baseball, tennis, fencing, cricket, boxing, and mixed martial arts.
Types
Right-handedness
is the most common type. Right-handed people are more skillful with
their right hands. Studies suggest that approximately 90% of people are
right-handed.
Left-handedness is less common. Studies suggest that approximately 10% of people are left-handed.
Ambidexterity
refers to having equal ability in both hands. Those who learn it still
tend to favor their originally dominant hand. This is uncommon, with
about a 1% prevalence.
Mixed-handedness or cross-dominance is the change of hand preference between different tasks. This is about as widespread as left-handedness. This is highly associated with the person's childhood brain development.
Measurement
Handedness may be measured behaviourally (performance measures) or through questionnaires (preference measures). The Edinburgh Handedness Inventory has been used since 1971 but contains some dated questions and is hard to score. Revisions have been published by Veale and by Williams.
The longer Waterloo Handedness Questionnaire is not widely accessible.
More recently, the Flinders Handedness Survey (FLANDERS) has been
developed.
Evolution
Some
non-human primates have a preferred hand for tasks, but they do not
display a strong right-biased preference like modern humans, with
individuals equally split between right-handed and left-handed
preferences. When exactly a right handed preference developed in the
human lineage is unknown, though it is known through various means that Neanderthals
had a right-handedness bias like modern humans. Attempts to determine
handedness of early humans by analysing the morphology of lithic
artefacts have been found to be unreliable.
Causes
There are several theories of how handedness develops.
Genetic factors
Handedness
displays a complex inheritance pattern. For example, if both parents of
a child are left-handed, there is a 26% chance of that child being
left-handed. A large study of twins from 25,732 families by Medland et al. (2006) indicates that the heritability of handedness is roughly 24%.
Two theoretical single-gene models have been proposed to explain the patterns of inheritance of handedness, by Marian Annett of the University of Leicester, and by Chris McManus of UCL.
However, growing evidence from linkage and genome-wide association studies suggests that genetic variance in handedness cannot be explained by a single genetic locus. From these studies, McManus et al. now conclude that handedness is polygenic and estimate that at least 40 loci contribute to the trait.
Brandler et al. performed a genome-wide association study for a measure of relative hand skill and found that genes involved in the determination of left-right asymmetry in the body play a key role in handedness. Brandler and Paracchini suggest the same mechanisms that determine left-right asymmetry in the body (e.g. nodal signaling and ciliogenesis) also play a role in the development of brain asymmetry
(handedness being a reflection of brain asymmetry for motor function).
In 2019, Wiberg et al. performed a genome-wide association study
and found that handedness was significantly associated with four loci,
three of them in genes encoding proteins involved in brain development.
Prenatal hormone exposure
Four studies have indicated that individuals who have had in-utero exposure to diethylstilbestrol (a synthetic estrogen
based medication used between 1940 and 1971) were more likely to be
left-handed over the clinical control group. Diethylstilbestrol animal
studies "suggest that estrogen affects the developing brain, including
the part that governs sexual behavior and right and left dominance".
Ultrasound
Another theory is that ultrasound
may sometimes affect the brains of unborn children, causing higher
rates of left-handedness in children whose mothers receive ultrasound
during pregnancy. Research suggests there may be a weak association
between ultrasound screening (sonography used to check the healthy development of the fetus and mother) and left-handedness.
Epigenetic markers
Twin studies indicate that genetic factors explain 25% of the variance in handedness, and environmental factors the remaining 75%. While the molecular basis of handedness epigenetics is largely unclear, Ocklenburg et al. (2017) found that asymmetric methylation of CpG sites plays a key role for gene expression asymmetries related to handedness.
Language dominance
One
common handedness theory is the brain hemisphere division of labor. In
most people, the left side of the brain controls speaking. The theory
suggests it is more efficient for the brain to divide major tasks
between the hemispheres—thus most people may use the non-speaking
(right) hemisphere for perception and gross motor skills. As speech is a
very complex motor control task, the specialised fine motor areas
controlling speech are most efficiently used to also control fine motor
movement in the dominant hand. As the right hand is controlled by the
left hemisphere (and the left hand is controlled by the right
hemisphere) most people are, therefore right-handed. The theory depends
on left-handed people having a reversed organisation. However, the majority of left-handers have been found to have left-hemisphere language dominance—just like right-handers.
Only around 30% of left-handers are not left-hemisphere dominant for
language. Some of those have reversed brain organisation, where the
verbal processing takes place in the right-hemisphere and visuospatial
processing is dominant to the left hemisphere.
Others have more ambiguous bilateral organisation, where both
hemispheres do parts of typically lateralised functions. When tasks
designed to investigate lateralisation (preference for handedness) are
averaged across a group of left-handers, the overall effect is that
left-handers show the same pattern of data as right-handers, but with a
reduced asymmetry. This finding is likely due to the small proportion of left-handers who have atypical brain organisation.
The majority of the evidence comes from literature assessing oral
language production and comprehension. When it comes to writing,
findings from recent studies were inconclusive for a difference in
lateralization for writing between left-handers and right-handers.
Developmental timeline
Researchers
studied fetuses in utero and determined that handedness in the womb was
a very accurate predictor of handedness after birth. In a 2013 study, 39% of infants (6 to 14 months) and 97% of toddlers (18 to 24 months) demonstrated a hand preference.
Infants have been observed to fluctuate heavily when choosing a
hand to lead in grasping and object manipulation tasks, especially in
one- versus two-handed grasping. Between 36 and 48 months, there is a
significant decline in variability between handedness in one-handed
grasping; it can be seen earlier in two-handed manipulation. Children of
18–36 months showed more hand preference when performing
bi-manipulation tasks than with simple grasping.
The decrease in handedness variability in children of 36–48
months may be attributable to preschool or kindergarten attendance due
to increased single-hand activities such as writing and coloring. Scharoun and Bryden noted that right-handed preference increases with age up to the teenage years.
Correlation with other factors
The
modern turn in handedness research has been towards emphasizing degree
rather than direction of handedness as a critical variable.
In his book Right-Hand, Left-Hand, Chris McManus of University College London
argues that the proportion of left-handers is increasing, and that an
above-average quota of high achievers have been left-handed. He says
that left-handers' brains are structured in a way that increases their
range of abilities, and that the genes that determine left-handedness
also govern development of the brain's language centers.
Studies in the U.K., U.S. and Australia have revealed
that left-handed people differ from right-handers by only one IQ point,
which is not noteworthy ... Left-handers' brains are structured
differently from right-handers' in ways that can allow them to process
language, spatial relations and emotions in more diverse and potentially
creative ways. Also, a slightly larger number of left-handers than
right-handers are especially gifted in music and math. A study of
musicians in professional orchestras found a significantly greater
proportion of talented left-handers, even among those who played
instruments that seem designed for right-handers, such as violins.
Similarly, studies of adolescents who took tests to assess mathematical
giftedness found many more left-handers in the population.
Left-handers are overrepresented among those with lower cognitive skills and mental impairments, with those with intellectual disability
being roughly twice as likely to be left-handed, as well as generally
lower cognitive and non-cognitive abilities amongst left-handed
children. Left-handers are nevertheless also overrepresented in high IQ societies, such as Mensa.
A 2005 study found that "approximately 20% of the members of Mensa are
lefthanded, double the proportion in most general populations".
Ghayas & Adil (2007) found that left-handers were significantly more likely to perform better on intelligence tests than right-handers and that right-handers also took more time to complete the tests.
In a systematic review and meta-analysis, Ntolka & Papadatou-Pastou
(2018) found that right-handers had higher IQ scores, but that
difference was negligible (about 1.5 points).
The prevalence of difficulties in left-right discrimination was investigated in a cohort of 2,720 adult members of Mensa and Intertel by Storfer.
According to the study, 7.2% of the men and 18.8% of the women
evaluated their left-right directional sense as poor or below average;
moreover participants who were relatively ambidextrous experienced
problems more frequently than did those who were more strongly left- or
right-handed. The study also revealed an effect of age, with younger participants reporting more problems.
Early childhood intelligence
Nelson,
Campbell, and Michel studied infants and whether developing handedness
during infancy correlated with language abilities in toddlers. In the
article they assessed 38 infants and followed them through to 12 months
and then again once they became toddlers from 18 to 24 months. They
discovered that when a child developed a consistent use of their right
or left hand during infancy (such as using the right hand to put the
pacifier back in, or grasping random objects with the left hand), they
were more likely to have superior language skills as a toddler. Children
who became lateral later than infancy (i.e., when they were toddlers)
showed normal development of language and had typical language scores.
The researchers used Bayley scales of infant and toddler development to assess the subjects.
Music
In two studies, Diana Deutsch
found that left-handers, particularly those with mixed-hand preference,
performed significantly better than right-handers in musical memory
tasks.
There are also handedness differences in perception of musical
patterns. Left-handers as a group differ from right-handers, and are
more heterogeneous than right-handers, in perception of certain stereo
illusions, such as the octave illusion, the scale illusion, and the glissando illusion.
Health
Studies
have found a positive correlation between left-handedness and several
specific physical and mental disorders and health problems, including:
Lower-birth-weight and complications at birth are positively correlated with left-handedness.
A 2012 study showed that nearly 40% of children with cerebral palsy were left-handed, while another study demonstrated that left-handedness was associated with a 62% increased risk of Parkinson's disease in women, but not in men. Another study suggests that the risk of developing multiple sclerosis increases for left-handed women, but the effect is unknown for men at this point.
Left-handed women may have a higher risk of breast cancer than right-handed women and the effect is greater in post-menopausal women.
At least one study maintains that left-handers are more likely to suffer from heart disease, and are more likely to have reduced longevity from cardiovascular causes.
Left-handers may be more likely to suffer bone fractures.
Left-handers have a lower prevalence of arthritis and ulcer.
One systematic review concluded: "Left-handers showed no systematic tendency to suffer from disorders of the immune system".
As handedness is a highly heritable trait associated with various
medical conditions, and because many of these conditions could have
presented a Darwinian fitness challenge in ancestral populations, this
indicates left-handedness may have previously been rarer than it
currently is, due to natural selection. However, on average,
left-handers have been found to have an advantage in fighting and
competitive, interactive sports, which could have increased their
reproductive success in ancestral populations.
Income
In a 2006 better correlate with the lateralization for writing compared to the other measures of study, researchers from Lafayette College and Johns Hopkins University
concluded that there was no statistically significant correlation
between handedness and earnings for the general population, but among
college-educated people, left-handers earned 10 to 15% more than their
right-handed counterparts.
In a 2014 study published by the National Bureau of Economic Research, Harvard
economist Joshua Goodman finds that left-handed people earn 10 to 12
percent less over the course of their lives than right-handed people.
Goodman attributes this disparity to higher rates of emotional and
behavioral problems in left-handed people.
Interactive sports such as table tennis, badminton and cricket have
an overrepresentation of left-handedness, while non-interactive sports
such as swimming show no overrepresentation. Smaller physical distance
between participants increases the overrepresentation. In fencing, about half the participants are left-handed. In tennis, 40% of the seeded players are left-handed. The term southpaw is sometimes used to refer to a left-handed individual, especially in baseball and boxing. Some studies suggest that right handed male athletes tend to be statistically taller and heavier than left handed ones.
Other, sports-specific factors may increase or decrease the advantage left-handers usually hold in one-on-one situations:
In cricket,
the overall advantage of a bowler's left-handedness exceeds that
resulting from experience alone: even disregarding the experience factor
(i.e., even for a batter whose experience against left-handed
bowlers equals their experience against right-handed bowlers), a
left-handed bowler challenges the average (i.e.,
right-handed) batter more than a right-handed bowler does, because the
angle of a bowler's delivery to an opposite-handed batter is much more
penetrating than that of a bowler to a same-handed batter (see Wasim Akram).
In baseball, a right-handed pitcher's curve ball
will break away from a right-handed batter and towards a left-handed
batter (batting left or right does not indicate left or right
handedness). While studies of handedness show that only 10% of the
general population is left-handed, the proportion of left-handed MLB players is closer to 39% of hitters and 28% of pitchers, according to 2012 data. Historical batting averages show that left-handed batters have a slight advantage over right-handed batters when facing right-handed pitchers.
Because there are fewer left-handed pitchers than right-handed
pitchers, left-handed batters have more opportunities to face
right-handed pitchers than their right-handed counterparts have against
left-handed pitchers. Fifteen of the top twenty career batting average leaders in Major League Baseball history have been posted by left-handed batters.
Left-handed batters have a slightly shorter run from the batter's box
to first base than right-handers. This gives left-handers a slight
advantage in beating throws to first base on infield ground balls.
Perhaps more important, the follow through of a left-handed swing
provides momentum in the direction of first base, while the right handed
batter must overcome the swing momentum towards third base before
beginning his run.
Because a left-handed pitcher faces first base when he is in
position to throw to the batter, whereas a right-handed pitcher has his
back to first base, a left-handed pitcher has an advantage when
attempting to pick off baserunners at first base.
Defensively in baseball, left-handedness is considered an advantage for first basemen
because they are better suited to fielding balls hit in the gap between
first and second base, and because they do not have to pivot their body
around before throwing the ball to another infielder.
For the same reason, the other infielder's positions are seen as being
advantageous to right-handed throwers. Historically, there have been few
left-handed catchers because of the perceived disadvantage a
left-handed catcher would have in making the throw to third base,
especially with a right-handed hitter at the plate. A left-handed catcher would have a potentially more dangerous time tagging out a baserunner trying to score.
With the ball in the glove on the right hand, a left-handed catcher
would have to turn his body to the left to tag a runner. In doing so, he
can lose the opportunity to brace himself for an impending collision. On the other hand, the Encyclopedia of Baseball Catchers states:
One advantage is a left-handed
catcher's ability to frame a right-handed pitcher's breaking balls. A
right-handed catcher catches a right-hander's breaking ball
across his body, with his glove moving out of the strike zone. A
left-handed catcher would be able to catch the pitch moving into the
strike zone and create a better target for the umpire.
In four wall handball,
typical strategy is to play along the left wall forcing the opponent to
use their left hand to counter the attack and playing into the strength
of a left-handed competitor.
In handball,
left-handed players have an advantage on the right side of the field
when attacking, getting a better angle, and that defenders might be
unused to them. Since few people are left-handed, there is a demand for
such players.
In water polo,
the centre forward position has an advantage in turning to shoot on net
when rotating the reverse direction as expected by the centre of the
opposition defence and gain an improved position to score. Left-handed
drivers are usually on the right side of the field, because they can get
better angles to pass the ball or shoot for goal.
Ice hockey typically uses a strategy in which a defence pairing
includes one left-handed and one right-handed defender. A
disproportionately large number of ice hockey players of all positions,
62 percent, shoot left, though this does not necessarily indicate
left-handedness.
In American football, the handedness of a quarterback affects blocking patterns on the offensive line. Tight ends, when only one is used, typically line up on the same side as the throwing hand of the quarterback, while the offensive tackle
on the opposite hand, which protects the quarterback's "blind side", is
typically the most valued member of the offensive line. Receivers also
have to adapt to the opposite spin. While uncommon, there have been several notable left-handed quarterbacks.
In bowling, the oil pattern used on the bowling lane breaks down
faster the more times a ball is rolled down the lane. Bowlers must
continually adjust their shots to compensate for the ball's change in
rotation as the game or series is played and the oil is altered from its
original pattern. A left-handed bowler competes on the opposite side of
the lane from the right-handed bowler and therefore deals with less
breakdown of the original oil placement. This means left-handed bowlers
have to adjust their shot less frequently than right-handed bowlers in
team events or qualifying rounds where there are possibly 4-10 people
per set of two lanes. This can allow them to stay more consistent.
However, this advantage is not present in bracket rounds and tournament
finals where matches are 1v1 on a pair of lanes.
Sex
According to a meta-analysis of 144 studies, totaling 1,787,629 participants, the best estimate for the male to female odds ratio
was 1.23, indicating that men are 23% more likely to be left-handed.
For example, if the incidence of female left-handedness was 10%, then
the incidence of male left-handedness would be approximately 12% (10%
incidence of left-handedness among women multiplied by an odds ratio of
1:1.23 for women:men results in a 12.3% incidence of left-handedness
among men).
Some studies examining the relationship between handedness and sexual
orientation have reported that a disproportionate minority of
homosexual people exhibit left-handedness, though findings are mixed.
A 2001 study also found that people assigned male at birth whose gender identity did not align with their assigned sex, were more than twice as likely to be left-handed than a clinical control group (19.5% vs. 8.3%, respectively).
Paraphilias
(atypical sexual interests) have also been linked to higher rates of
left-handedness. A 2008 study analyzing the sexual fantasies of 200
males found "elevated paraphilic interests were correlated with elevated
non-right handedness". Greater rates of left-handedness have also been documented among pedophiles.
A 2014 study attempting to analyze the biological markers of asexuality
asserts that non-sexual men and women were 2.4 and 2.5 times,
respectively, more likely to be left-handed than their heterosexual
counterparts.
Mortality rates in combat
A study at Durham University—which examined mortality data for cricketers
whose handedness was a matter of public record—found that left-handed
men were almost twice as likely to die in war as their right-handed
contemporaries.
The study theorised that this was because weapons and other equipment
was designed for the right-handed. "I can sympathise with all those
left-handed cricketers who have gone to an early grave trying
desperately to shoot straight with a right-handed Lee Enfield .303",
wrote a journalist reviewing the study in the cricket press.
The findings echo those of previous American studies, which found that
left-handed US sailors were 34% more likely to have a serious accident
than their right-handed counterparts.
Episodic memory
A high level of handedness (whether strongly favoring right or left) is associated with poorer episodic memory, and with poorer communication between brain hemispheres, which may give poorer emotional processing, although bilateral stimulation may reduce such effects.
Corpus callosum
A high level of handedness is associated with a smaller corpus callosum whereas low handedness with a larger one.
Many
tools and procedures are designed to facilitate use by right-handed
people, often without realizing the difficulties incurred by the
left-handed. John W. Santrock has written, "For centuries, left-handers
have suffered unfair discrimination in a world designed for
right-handers."
Many products for left-handed use are made by specialist
producers, although not available from normal suppliers. Items as simple
as a knife ground for use with the right hand are less convenient for
left-handers. There is a multitude of examples: kitchen tools such as knives, corkscrews and scissors, garden tools, and so on. While not requiring a purpose-designed product, there are more appropriate ways for left-handers to tie shoelaces.
There are companies that supply products designed specifically for
left-handed use. One such is Anything Left-Handed, which in 1967 opened a
shop in Soho, London; the shop closed in 2006, but the company
continues to supply left-handed products worldwide by mail order.
Writing from left to right as in many languages, in particular,
with the left hand covers and tends to smear (depending upon ink drying)
what was just written. Left-handed writers have developed various ways
of holding a pen for best results. For using a fountain pen, preferred by many left-handers, nibs ground to optimise left-handed use (pushing rather than pulling across the paper) without scratching are available.
McManus noted that, as the Industrial Revolution
spread across Western Europe and the United States in the 19th century,
workers needed to operate complex machines that were designed with
right-handers in mind. This would have made left-handers more visible
and at the same time appear less capable and more clumsy. Writing
left-handed with a dip pen, in particular, was prone to blots and
smearing.
Negative connotations and discrimination
Moreover,
apart from inconvenience, left-handed people have historically been
considered unlucky or even malicious for their difference by the
right-handed majority. In many languages, including English, the word
for the direction "right" also means "correct" or "proper". Throughout
history, being left-handed was considered negative, or evil.
The Latin adjective sinister
means "left" as well as "unlucky", and this double meaning survives in
European derivatives of Latin, including the English words "sinister"
(meaning both 'evil' and 'on the bearer's left on a coat of arms') and
"ambisinister" meaning 'awkward or clumsy with both or either hand'.
There are many negative connotations associated with the phrase
"left-handed": clumsy, awkward, unlucky, insincere, sinister, malicious,
and so on. A "left-handed compliment" is one that has two meanings, one
of which is unflattering to the recipient. In French, gauche means both "left" and "awkward" or "clumsy", while droit(e) (cognate to English direct
and related to "adroit") means both "right" and "straight", as well as
"law" and the legal sense of "right". The name "Dexter" derives from the
Latin for "right", as does the word "dexterity" meaning manual skill.
As these are all very old words, they would tend to support theories
indicating that the predominance of right-handedness is an extremely old
phenomenon.
Before the development of fountain pens and other writing instruments, children were taught to write with a dip pen.
While a right-hander could smoothly drag the pen across paper from left
to right, a dip pen could not easily be pushed across by the left hand
without digging into the paper and making blots and stains.
Even with more modern pens, writing from left to right, as in many
languages, with the left hand covers and can smear what was just written
when moving across the line.
Into the 20th and even the 21st century, left-handed children in Uganda were beaten by schoolteachers or parents for writing with their left hand, or had their left hands tied behind their backs to force them to write with their right hand. As a child, the future British king George VI
(1895–1952) was naturally left-handed. He was forced to write with his
right hand, as was common practice at the time. He was not expected to
become king, so that was not a factor.
Until very recently in Taiwan, left-handed people were forced to switch to being right-handed, or at least switch to writing with the right hand. Due to the importance of stroke order,
developed for the comfortable use of right-handed people, it is
considered more difficult to write legible Chinese characters with the
left hand than it is to write Latin letters, though difficulty is
subjective and depends on the writer.
Because writing when moving one's hand away from its side towards the
other side of the body can cause smudging if the outward side of the
hand is allowed to drag across the writing, writing in the Latin alphabet
might possibly be less feasible with the left hand than the right under
certain circumstances. Conversely, right-to-left alphabets, such as the
Arabic and Hebrew, are generally considered easier to write with the
left hand.
Depending on the position and inclination of the writing paper, and the
writing method, the left-handed writer can write as neatly and
efficiently or as messily and slowly as right-handed writers. Usually
the left-handed child needs to be taught how to write correctly with the
left hand, since discovering a comfortable left-handed writing method
on one's own may not be straightforward.
In the Soviet school system, all left-handed children were forced to write with their right hand.
International Left-Handers Day is held annually every August 13. It was founded by the Left-Handers Club in 1992, with the club itself having been founded in 1990.
International Left-Handers Day is, according to the club, "an annual
event when left-handers everywhere can celebrate their sinistrality
(left-handedness) and increase public awareness of the advantages and
disadvantages of being left-handed."
It celebrates their uniqueness and differences, who are from seven to
ten percent of the world's population. Thousands of left-handed people
in today's society have to adapt to use right-handed tools and objects.
Again according to the club, "in the U.K. alone there were over 20
regional events to mark the day in 2001 – including left-v-right sports
matches, a left-handed tea party, pubs using left-handed corkscrews
where patrons drank and played pub games with the left hand only, and
nationwide 'Lefty Zones' where left-handers' creativity, adaptability
and sporting prowess were celebrated, whilst right-handers were
encouraged to try out everyday left-handed objects to see just how
awkward it can feel using the wrong equipment."
In other animals
Kangaroos and other macropodmarsupials
show a left-hand preference for everyday tasks in the wild. 'True'
handedness is unexpected in marsupials however, because unlike placental mammals, they lack a corpus callosum. Left-handedness was particularly apparent in the red kangaroo (Macropus rufus) and the eastern gray kangaroo (Macropus giganteus). Red-necked (Bennett's) wallabies (Macropus rufogriseus)
preferentially use their left hand for behaviours that involve fine
manipulation, but the right for behaviours that require more physical
strength. There was less evidence for handedness in arboreal species.
Studies of dogs, horses, and domestic cats have shown that females of
those species tend to be right-handed, while males tend to be
left-handed.
Rayleigh scattering causes the blue color of the daytime sky and the reddening of the Sun at sunset.
Rayleigh scattering (/ˈreɪli/RAY-lee) is the scattering or deflection of light, or other electromagnetic radiation, by particles with a size much smaller than the wavelength of the radiation. For light frequencies well below the resonance frequency of the scattering medium (normal dispersion regime), the amount of scattering is inversely proportional to the fourth power
of the wavelength (e.g., a blue color is scattered much more than a red
color as light propagates through air). The phenomenon is named after
the 19th-century British physicist Lord Rayleigh (John William Strutt).
Due
to Rayleigh scattering, red and orange colors are more visible during
sunset because the blue and violet light has been scattered out of the
direct path. Due to removal of such colors, these colors are scattered
by dramatically colored skies and monochromatic rainbows.
Rayleigh scattering results from the electric polarizability
of the particles. The oscillating electric field of a light wave acts
on the charges within a particle, causing them to move at the same
frequency. The particle, therefore, becomes a small radiating dipole
whose radiation we see as scattered light. The particles may be
individual atoms or molecules; it can occur when light travels through
transparent solids and liquids, but is most prominently seen in gases.
Scattering by particles with a size comparable to, or larger than, the wavelength of the light is typically treated by the Mie theory, the discrete dipole approximation
and other computational techniques. Rayleigh scattering applies to
particles that are small with respect to wavelengths of light, and that
are optically "soft" (i.e., with a refractive index close to 1). Anomalous diffraction theory applies to optically soft but larger particles.
History
In 1869, while attempting to determine whether any contaminants remained in the purified air he used for infrared experiments, John Tyndall discovered that bright light scattering off nanoscopic particulates was faintly blue-tinted. He conjectured that a similar scattering of sunlight gave the sky its blue hue, but he could not explain the preference for blue light, nor could atmospheric dust explain the intensity of the sky's color.
The size of a scattering particle is often parameterized by the ratio
where r is the particle's radius, λ is the wavelength of the light and x is a dimensionless parameter
that characterizes the particle's interaction with the incident
radiation such that: Objects with x ≫ 1 act as geometric shapes,
scattering light according to their projected area. At the intermediate x
≃ 1 of Mie scattering, interference effects develop through phase
variations over the object's surface. Rayleigh scattering applies to
the case when the scattering particle is very small (x ≪ 1, with a
particle size < 1/10 of wavelength)
and the whole surface re-radiates with the same phase. Because the
particles are randomly positioned, the scattered light arrives at a
particular point with a random collection of phases; it is incoherent and the resulting intensity is just the sum of the squares of the amplitudes from each particle and therefore proportional to the inverse fourth power of the wavelength and the sixth power of its size. The wavelength dependence is characteristic of dipole scattering
and the volume dependence will apply to any scattering mechanism. In
detail, the intensity of light scattered by any one of the small spheres
of radius r and refractive indexn from a beam of unpolarized light of wavelength λ and intensity I0 is given by
where R is the distance to the particle and θ is the scattering angle. Averaging this over all angles gives the Rayleigh scattering cross-section of the particles in air:
Here n is the refractive index of the spheres that approximate
the molecules of the gas; the index of the gas surrounding the spheres
is neglected, an approximation that introduces an error of less than
0.05%.
The fraction of light scattered by scattering particles over the
unit travel length (e.g., meter) is the number of particles per unit
volume N times the cross-section. For example, air has a refractive index of 1.0002793 at atmospheric pressure, where there are about 2×1025 molecules per cubic meter, and therefore the major constituent of the atmosphere, nitrogen, has a Rayleigh cross section of 5.1×10−31 m2 at a wavelength of 532 nm (green light). This means that about a fraction 10−5 of the light will be scattered for every meter of travel.
The strong wavelength dependence of the scattering (~λ−4) means that shorter (blue) wavelengths are scattered more strongly than longer (red) wavelengths.
From molecules
Figure showing the greater proportion of blue light scattered by the atmosphere relative to red light
The expression above can also be written in terms of individual
molecules by expressing the dependence on refractive index in terms of
the molecular polarizabilityα,
proportional to the dipole moment induced by the electric field of the
light. In this case, the Rayleigh scattering intensity for a single
particle is given in CGS-units by
and in SI-units by
Effect of fluctuations
When the dielectric constant of a certain region of volume is different from the average dielectric constant of the medium , then any incident light will be scattered according to the following equation
where represents the variance of the fluctuation in the dielectric constant .
Rayleigh scattering of that light off oxygen and nitrogen molecules, and
the response of the human visual system.
The strong wavelength dependence of the Rayleigh scattering (~λ−4) means that shorter (blue) wavelengths are scattered more strongly than longer (red)
wavelengths. This results in the indirect blue and violet light coming
from all regions of the sky. The human eye responds to this wavelength
combination as if it were a combination of blue and white light.
Some of the scattering can also be from sulfate particles. For years after large Plinian eruptions, the blue cast of the sky is notably brightened by the persistent sulfate load of the stratospheric gases. Some works of the artist J. M. W. Turner may owe their vivid red colours to the eruption of Mount Tambora in his lifetime.
In locations with little light pollution, the moonlit night sky is also blue, because moonlight is reflected sunlight, with a slightly lower color temperature
due to the brownish color of the Moon. The moonlit sky is not perceived
as blue, however, because at low light levels human vision comes mainly
from rod cells that do not produce any color perception (Purkinje effect).
Of sound in amorphous solids
Rayleigh scattering is also an important mechanism of wave scattering in amorphous solids
such as glass, and is responsible for acoustic wave damping and phonon
damping in glasses and granular matter at low or not too high
temperatures.
This is because in glasses at higher temperatures the Rayleigh-type
scattering regime is obscured by the anharmonic damping (typically with a
~λ−2 dependence on wavelength), which becomes increasingly more important as the temperature rises.
In amorphous solids – glasses – optical fibers
Rayleigh scattering is an important component of the scattering of optical signals in optical fibers.
Silica fibers are glasses, disordered materials with microscopic
variations of density and refractive index. These give rise to energy
losses due to the scattered light, with the following coefficient:
where n is the refraction index, p is the photoelastic coefficient of the glass, k is the Boltzmann constant, and β is the isothermal compressibility. Tf is a fictive temperature, representing the temperature at which the density fluctuations are "frozen" in the material.
In porous materials
Rayleigh scattering in opalescent glass: it appears blue from the side, but orange light shines through.
Rayleigh-type λ−4 scattering can also be exhibited by porous materials. An example is the strong optical scattering by nanoporous materials. The strong contrast in refractive index between pores and solid parts of sintered alumina results in very strong scattering, with light completely changing direction each five micrometers on average. The λ−4-type scattering is caused by the nanoporous structure (a narrow pore size distribution around ~70 nm) obtained by sintering monodispersive alumina powder.
.jpg)
.jpg)
