Editing Pendulum (section)

== Other uses ==

=== Seismometers ===
A pendulum in which the rod is not vertical but almost horizontal was used in early [[seismometers]] for measuring Earth tremors. The bob of the pendulum does not move when its mounting does, and the difference in the movements is recorded on a drum chart.

=== Schuler tuning ===
{{Main|Schuler tuning}}
As first explained by [[Max Schuler|Maximilian Schuler]] in a 1923 paper, a pendulum whose period exactly equals the orbital period of a hypothetical satellite orbiting just above the surface of the Earth (about 84 minutes) will tend to remain pointing at the center of the Earth when its support is suddenly displaced. This principle, called [[Schuler tuning]], is used in [[inertial guidance system]]s in ships and aircraft that operate on the surface of the Earth. No physical pendulum is used, but the [[control system]] that keeps the [[inertial platform]] containing the [[gyroscope]]s stable is modified so the device acts as though it is attached to such a pendulum, keeping the platform always facing down as the vehicle moves on the curved surface of the Earth.

=== Coupled pendulums ===
[[File:Coupled oscillators.gif|frame|Two pendulums with the same period coupled by suspending them from a common support string. The oscillation alternates between the two.]]
[[File:Huygens synchronization of two clocks (Experiment).jpg|thumbnail|left|100px|Repetition of Huygens experiment showing synchronization of two clocks]]
{{main|Injection locking}}
In 1665 Huygens made a curious observation about pendulum clocks. Two clocks had been placed on his [[mantlepiece]], and he noted that they had acquired an opposing motion. That is, their pendulums were beating in unison but in the opposite direction; 180° [[out of phase]]. Regardless of how the two clocks were started, he found that they would eventually return to this state, thus making the first recorded observation of a [[Coupled oscillation|coupled oscillator]].<ref>{{cite web
 | last=Toon | first=John | date=2000-09-08
 | url=http://gtresearchnews.gatech.edu/newsrelease/PENDULUM.html
 | title=Out of Time: Researchers Recreate 1665 Clock Experiment to Gain Insights into Modern Synchronized Oscillators
 | publisher=Georgia Tech | access-date=2007-05-31 }}</ref>

The cause of this behavior was that the two pendulums were affecting each other through slight motions of the supporting mantlepiece. This process is called [[entrainment (physics)|entrainment]] or [[mode locking]] in physics and is observed in other coupled oscillators. Synchronized pendulums have been used in clocks and were widely used in [[gravimeter]]s in the early 20th century. Although Huygens only observed out-of-phase synchronization, recent investigations have shown the existence of in-phase synchronization, as well as "death" states wherein one or both clocks stops.<ref>{{cite journal|author1=A.L. Fradkov|author2=B. Andrievsky|title=Synchronization and phase relations in the motion of two-pendulum system|journal=International Journal of Non-linear Mechanics|volume=42|date=2007|issue=6 |pages=895–901|doi=10.1016/j.ijnonlinmec.2007.03.016 |bibcode=2007IJNLM..42..895F }}</ref><ref>{{cite book|author=I.I. Blekhman|title=Synchronization in science and technology|publisher=ASME Press|location=New York|date=1988}}</ref>

=== Religious practice ===
[[File:Catedral Metropolitana, México D.F., México, 2013-10-16, DD 89.JPG|thumb|Pendulum in the Metropolitan Cathedral, Mexico City]]
Pendulum motion appears in religious ceremonies as well. The swinging [[incense]] burner called a [[censer]], also known as a [[thurible]], is an example of a pendulum.<ref>An interesting simulation of thurible motion can be found at [http://www.sciences.univ-nantes.fr/physique/perso/gtulloue/Meca/Oscillateurs/botafumeiro.html#manip this site] {{Webarchive|url=https://web.archive.org/web/20110523233141/http://www.sciences.univ-nantes.fr/physique/perso/gtulloue/Meca/Oscillateurs/botafumeiro.html#manip |date=2011-05-23 }}.</ref> Pendulums are also seen at many gatherings in eastern Mexico where they mark the turning of the tides on the day which the tides are at their highest point. Pendulums may also be used for [[dowsing]].

=== Education ===

Pendulums are widely used in [[science education]] as an example of a [[harmonic oscillator]], to teach [[dynamics (mechanics)|dynamics]] and [[oscillatory motion]].  One use is to demonstrate the law of [[conservation of energy]].<ref name=Hart>{{cite web|last1=Hart|first1=Matthew|title=Physics Risks Death by Wrecking Ball for Science|url=http://nerdist.com/physics-risks-death-by-wrecking-ball-for-science/|website=Nerdist|access-date=14 March 2017|language=en|date=2 February 2016|archive-date=15 March 2017|archive-url=https://web.archive.org/web/20170315085935/http://nerdist.com/physics-risks-death-by-wrecking-ball-for-science/|url-status=dead}}</ref><ref>{{cite book|last1=Sorenson|first1=Roy|editor1-last=Booth|editor1-first=Anthony Robert|editor2-last=Rowbottom|editor2-first=Darrell P.|title=Intuitions|date=2014|publisher=Oxford Univ Pr|isbn=9780199609192|page=139|chapter-url=https://books.google.com/books?id=ttX1AwAAQBAJ&q=bowling+ball+pendulum+experiment&pg=PA139|access-date=15 March 2017|chapter=Novice Thought Experiments}}</ref> A heavy object such as a [[bowling ball]]<ref>{{cite web|title=Bowling Ball Pendulum|url=http://wonders.physics.wisc.edu/bowling-ball-pendulum.htm|website=The Wonders of Physics|publisher=University of Wisconsin–Madison|access-date=14 March 2017|language=en}}</ref> or [[wrecking ball]]<ref name=Hart/> is attached to a string. The weight is then moved to within a few inches of a volunteer's face, then released and allowed to swing and come back. In most instances, the weight reverses direction and then returns to (almost) the same position as the original release location — ''i.e.'' a small distance from the volunteer's face — thus leaving the volunteer unharmed. On occasion the volunteer is injured if either the volunteer does not stand still<ref>{{cite web|last1=weknowmemes|title=Physics Ball Test Gone Wrong|url=https://www.youtube.com/watch?v=teqsNtYbJAY| archive-url=https://ghostarchive.org/varchive/youtube/20211110/teqsNtYbJAY| archive-date=2021-11-10 | url-status=live|website=YouTube|access-date=14 March 2017|date=8 August 2014}}{{cbignore}}</ref> or the pendulum is initially released with a push (so that when it returns it surpasses the release position).

=== Torture device ===
[[File:PitandthePendulum-Clarke.jpg|thumb|Illustration to [[Edgar Allan Poe]]’s [[The Pit and the Pendulum]] by [[Harry Clarke]]]]
It is claimed that the pendulum was used as an instrument of [[torture]] and [[execution]] by the [[Spanish Inquisition]]<ref name="Scott">{{cite book
 | last1  = Scott
 | first1 = George Ryley
 | title  = The History Of Torture Throughout the Ages
 | publisher = Routledge
 | date   = 2009
 | pages  = 242
 | url    = https://books.google.com/books?id=PVPYAQAAQBAJ&q=pendulum&pg=PA242
 | isbn   = 978-1136191602
 }}</ref> in the 18th century. The allegation is contained in the 1826 book ''The history of the Inquisition of Spain ''  by the Spanish priest, historian and [[Classical liberalism|liberal]] activist [[Juan Antonio Llorente]].<ref name="Llorente">{{cite book
 | last1  = Llorente
 | first1 = Juan Antonio 
 | title  = The history of the Inquisition of Spain. Abridged and translated by George B. Whittaker
 | publisher = Oxford University
 | date   = 1826
 | pages  = XX, preface
 | url    = https://books.google.com/books?id=oZS63BNSlLMC&q=pendulum&pg=PR20
 }}</ref>  A swinging pendulum whose edge is a knife blade slowly descends toward a bound prisoner until it cuts into his body.<ref name="Abbott" >{{cite book |title=Execution: The Guillotine, the Pendulum, the Thousand Cuts, the Spanish Donkey, and 66 Other Ways of Putting Someone to Death |last= Abbott |first=Geoffrey |year=2006 |publisher=St. Martin's Press |isbn=978-0-312-35222-6}}</ref>  This method of torture came to popular consciousness through the 1842 short story "[[The Pit and the Pendulum]]" by American author [[Edgar Allan Poe]].<ref name="Poe">{{cite book
 | last  = Poe
 | first = Edgar Allan
 | title  = The Pit and the Pendulum
 | publisher = Booklassic
 | date   = 1842
 | url    = https://books.google.com/books?id=86IQCgAAQBAJ
 | isbn   = 978-9635271900
 }}</ref>

Most knowledgeable sources are skeptical that this torture was ever actually used.<ref name="Roth">{{cite book
 | last  = Roth
 | first = Cecil 
 | title  = The Spanish Inquisition
 | publisher = W. W. Norton and Company 
 | date   = 1964
 | pages  = [https://archive.org/details/spanishinquisiti00ceci/page/258 258]
 | url    = https://archive.org/details/spanishinquisiti00ceci
 | url-access = registration
 | quote = pendulum.
 | isbn   = 978-0-393-00255-3
 }}</ref><ref name="Mannix">{{cite book
 | last  = Mannix
 | first = Daniel P.
 | title  = The History of Torture
 | publisher = eNet Press
 | date   = 2014
 | pages  = 76
 | url    = https://books.google.com/books?id=ktX9AwAAQBAJ&q=pendulum&pg=PA76
 | isbn   = 978-1-61886-751-3
 }}</ref><ref name="Pavlac">{{cite book
 | last1  = Pavlac
 | first1 = Brian  
 | title  = Witch Hunts in the Western World: Persecution and Punishment from the Inquisition through the Salem Trials
 | publisher = ABC-CLIO
 | date   = 2009
 | pages  = 152
 | url    = https://books.google.com/books?id=cOmyAcgxFgAC&q=pendulum&pg=PA152
 | isbn   = 978-0-313-34874-7
 }}</ref>  The only evidence of its use is one paragraph in the preface to Llorente's  1826 ''History'',<ref name="Llorente" /> relating a second-hand account by a single prisoner released from the Inquisition's Madrid dungeon in 1820, who purportedly described the pendulum torture method.  Modern sources point out that due to Jesus' admonition against bloodshed, Inquisitors were only allowed to use torture methods which did not spill blood, and the pendulum method would have violated this stricture.  One theory is that Llorente misunderstood the account he heard; the prisoner was actually referring to another common Inquisition torture, the ''[[strappado]]'' (garrucha), in which the prisoner has his hands tied behind his back and is hoisted off the floor by a rope tied to his hands.<ref name="Pavlac" /> This method was also known as the "pendulum".  Poe's popular horror tale, and public awareness of the Inquisition's other brutal methods, has kept the myth of this elaborate torture method alive.

=== Pendulum wave ===
[[File:pendulum_wave_animation.svg|thumb|upright|link={{filepath:pendulum_wave_animation.svg}}|[[SVG animation]] of a pendulum wave]]
A [[pendulum wave]] is a physics demonstration and [[kinetic art]] comprising several uncoupled pendulums with different lengths. As the pendulums oscillate, they appear to produce travelling and standing waves, beating, and random motion.<ref>Harvard Natural Sciences Lecture Demonstrations, [http://sciencedemonstrations.fas.harvard.edu/presentations/pendulum-waves ''Pendulum Waves'']</ref>