Motion (physics)
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[[Image:Leaving Yongsan Station.jpg|300px|thumb|right|Motion involves change in position, such as in this perspective of rapidly leaving [[Yongsan Station]]]]
In [[physics]], '''motion''' means a continuous change in the location of a body. Change in motion is the result of applied [[force]]. Motion is typically described in terms of [[velocity]], [[acceleration]], [[Displacement (vector)|displacement]], and [[time]].<ref>[http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html Nave, R. 2005. Motion. HyperPhysics. Georgia State University]</ref> An object's [[momentum]] is directly related to the object's [[mass]] and [[velocity]], and is conserved within a system, as described by the [[Momentum#Conservation of momentum|law of conservation of momentum]].
Everything in the universe is moving.<ref>[http://www.nap.edu/html/oneuniverse/motion_20-21.html De Grasse Tyson, N., Liu, C., & Irion, R. 2000. One Universe: At home in the cosmos. p.20-21. Joseph Henry Press. ISBN-10: 0-309-06488-0]</ref> As there is no absolute reference system, ''absolute motion'' cannot be determined and only motion relative to a [[frame of reference|point of reference]] can be determined; this is emphasised by the term ''relative motion''.<ref>[http://www.colutron.com/download_files/chapt9.pdf Wåhlin, L. 1997. "THE DEADBEAT UNIVERSE"], Chapter 9. Colutron Research Corporation ISBN 0 933407 03 3</ref>
== Theories ==
Until the end of the 19th century, [[Isaac Newton]]'s [[Newton's laws of motion|laws of motion]], which he posited as axioms or postulates in his famous [[Philosophiae Naturalis Principia Mathematica|Principia]] were the basis of what has since become known as [[classical physics]]. Calculations of trajectories and forces of bodies in motion based on Newtonian or classical physics were very successful until physicists began to be able to measure and observe very fast physical phenomena.
At very high speeds, the equations of classical physics were not able to calculate accurate values. To address these problems, the ideas of [[Henri Poincaré]] and [[Albert Einstein]] concerning the fundamental phenomenon of motion were adopted in lieu of Newton's. Whereas Newton's laws of motion assumed absolute values of space and time in the equations of motion, the model of Einstein and Poincaré, now called the [[special theory of relativity]], assumed values for these concepts with arbitrary zero points. Because (for example) the special relativity equations yielded accurate results at high speeds and Newton's did not, the special relativity model is now accepted as explaining bodies in motion (when we ignore [[gravity]]). However, as a practical matter, Newton's equations are much easier to work with than those of special relativity and therefore are more often used in [[applied physics]] and [[engineering]].
In the Newtonian model, because motion is defined as the proportion of [[space]] to [[time]], these concepts are prior to motion, just as the concept of motion itself is prior to [[force]]. In other words, the properties of space and time determine the nature of motion and the properties of motion, in turn, determine the nature of force.
In the special relativistic model, motion can be thought of as something like an [[angle]] between a space direction and the time direction.
In special relativity and [[Euclidean space]], only relative motion can be measured, and absolute motion is meaningless.
=== Relative motion ===
Relative motion is a change in location relative to a reference point, as measured by a particular [[observation|observer]] in a particular [[frame of reference]]. Essentially, an object is in relative motion when its distance from another object is changing. However, whether the object appears to be moving or not depends on the point of view.<ref>[http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html Nave, R. 2005. Relative Motion. HyperPhysics. Georgia State University.]</ref> For example, a woman riding in a bus is not moving in relation to the seat she is sitting on, but she is moving in relation to the buildings the bus passes.
The place or object used for comparison to determine the change in position of an object is known as the reference point. Thus, if it is assumed that the reference point is stationary, an object can be said to be in motion if it changes position relative to a reference point. A classic misinterpretation of relative motion was the incorrect assumption that the [[Sun]] moved around the [[Earth]] rather than the other way around.
==List of "imperceptible" human motions==
Humans, like all things in the universe are in constant motion,<ref>[http://www.nap.edu/html/oneuniverse/motion_8-9.html De Grasse Tyson, N., Liu, C., & Irion, R. 2000. One Universe: At home in the cosmos. p.8-9. Joseph Henry Press. ISBN-10: 0-309-06488-0]</ref> however, aside from obvious movements of the various external [[anatomy|body]] parts and [[locomotion]], humans are in motion in a variety of ways which are more difficult to [[Motion perception|perceive]]. Many of these "imperceptible motions" are only perceivable with the help of special tools and careful observation. The larger scales of "imperceptible motions" are difficult for humans to perceive for two reasons: 1) [[Newton's laws of motion]] (particularly [[Inertia]]) which prevent humans from feeling motions of a mass to which they are connected, and 2) the lack of an obvious [[reference point|frame of reference]] which would allow individuals to easily see that they are moving.<ref>[http://www.physlink.com/education/askexperts/ae118.cfm Safkan, Y. 2007] "f the term 'absolute motion' has no meaning, then why do we say that the earth moves around the sun and not vice versa?" Ask the Experts. PhysicsLink</ref> The smaller scales of these motions are too small for [[human]]s to [[sense]].
=== Universe ===
*[[Spacetime]] (the fabric of the universe) is actually [[Metric expansion of space|expanding]]. Essentially, everything in the [[universe]] is stretching like a [[rubber band]]. This motion is the most obscure as it is not physical motion as such, but rather a change in the very nature of the universe. The primary source of verification of this expansion was provided by [[Edwin Hubble]] who demonstrated that all galaxies and distant astronomical objects were moving away from us (''"[[Hubble's law]]"'') as predicted by a universal expansion.<ref>Hubble, Edwin, "[http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1929PNAS...15..168H&db_key=AST&data_type=HTML&format=&high=42ca922c9c30954 A Relation between Distance and Radial Velocity among Extra-Galactic Nebulae]" (1929) ''Proceedings of the National Academy of Sciences of the United States of America'', Volume 15, Issue 3, pp. 168-173 ([http://www.pnas.org/cgi/reprint/15/3/168 Full article], PDF)</ref>
=== Galaxy ===
*The [[Milky Way Galaxy]], is hurtling through [[space]] at an incredible [[speed]]. It is powered by the [[force]] left over from the [[Big Bang]]. Many astronomers believe the Milky Way is moving at approximately 600 km/s relative to the observed locations of other nearby galaxies. Another reference frame is provided by the [[Cosmic microwave background]]. This frame of reference indicates that The Milky Way is moving at around 552 km/s.<ref name="dipole">{{cite journal
| author=Kogut, A.; Lineweaver, C.; Smoot, G. F.; Bennett, C. L.; Banday, A.; Boggess, N. W.; Cheng, E. S.; de Amici, G.; Fixsen, D. J.; Hinshaw, G.; Jackson, P. D.; Janssen, M.; Keegstra, P.; Loewenstein, K.; Lubin, P.; Mather, J. C.; Tenorio, L.; Weiss, R.; Wilkinson, D. T.; Wright, E. L.
| title=Dipole Anisotropy in the COBE Differential Microwave Radiometers First-Year Sky Maps
| journal=Astrophysical Journal
| year=1993
| volume=419
| pages=1
| url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1993ApJ...419....1K
| accessdate=2007-05-10 | doi = 10.1086/173453 <!--Retrieved from CrossRef by DOI bot-->
}}</ref>
=== Solar System ===
*The Milky Way is [[rotation|rotating]] around its [[density|dense]] [[galactic center]], thus the [[solar system]] is moving in a circle within the [[galaxy]]'s [[gravity]]. Away from the central bulge or outer rim, the typical stellar [[velocity]] is between 210 and 240 km/s.<ref name="fn4">{{cite web
| last=Imamura
| first=Jim
| date=[[August 10]] [[2006]]
| url=http://zebu.uoregon.edu/~imamura/123/lecture-2/mass.html
| title=Mass of the Milky Way Galaxy
| publisher=University of Oregon
| accessdate=2007-05-10 }}</ref>
=== Earth ===
*The Earth is [[rotation|rotating]] or spinning around its [[Axis of rotation|axis]], this is evidenced by [[day]] and [[night]], at the equator the earth has an eastward velocity of 0.4651 km/s (or 1040 mi/h).<ref name="nasa goodard">[http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970401c.html Ask and Astrophysicist]. NASA Goodard Space Flight Center.</ref>
*The Earth is [[orbit]]ing around the [[Sun]] in an [[orbital revolution]]. A complete orbit around the sun takes one [[year]] or about 365 days, it averages a speed of about 30 km/s (or 67,000 mi/h).<ref name="earth_fact_sheet">{{cite web | last = Williams | first = David R. | date = September 1, 2004 | url = http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html | title = Earth Fact Sheet | publisher = NASA | accessdate = 2007-03-17 }}</ref>
=== Continents ===
*The Theory of [[Plate tectonic]]s tells us that the [[continent]]s are drifting on [[convection current]]s within the [[Mantle (geology)|mantle]] causing them to move across the surface of the [[planet]] at the slow speed of approximately 1 [[inch]] (2.54 cm) per year.<ref>{{cite web
| author=Staff
| url =http://sideshow.jpl.nasa.gov/mbh/series.html
| title =GPS Time Series
| publisher =NASA JPL
| accessdate =2007-04-02 }}</ref><ref>{{cite web
| last =Huang
| first =Zhen Shao
| url =http://hypertextbook.com/facts/ZhenHuang.shtml
| title =Speed of the Continental Plates
| work =The Physics Factbook
| accessdate =2007-11-09
}}</ref> However, the velocities of plates range widely. The fastest-moving plates are the oceanic plates, with the [[Cocos Plate]] advancing at a rate of 75 mm/yr<ref>{{cite web
| author=Meschede, M.; Udo Barckhausen, U.
| date=November 20, 2000
| url = http://www-odp.tamu.edu/publications/170_SR/chap_07/chap_07.htm
| title = Plate Tectonic Evolution of the Cocos-Nazca Spreading Center
| work=Proceedings of the Ocean Drilling Program
| publisher = Texas A&M University
| accessdate = 2007-04-02
}}</ref> (3.0 in/yr) and the [[Pacific Plate]] moving 52–69 mm/yr (2.1–2.7 in/yr). At the other extreme, the slowest-moving plate is the [[Eurasian Plate]], progressing at a typical rate of about 21 mm/yr (0.8 in/yr).
=== Internal body ===
*The human [[heart]] is constantly contracting to move [[blood]] throughout the body. Through larger veins and arteries in the body blood has been found to travel at approximately 0.33 m/s.<ref>[http://www.coheadquarters.com/PennLibr/MyPhysiology/lect5/xpen5.01.htm Penny, P.] 2003. Hemodynamic: Blood Velocity</ref> Though considerable variation exists, and peak flows in the venae cavae have been found to range between 0.1 m/s and 0.45 m/s.<ref>{{cite journal
| author=LEWIS WEXLER, DEREK H. BERGEL, IVOR T. GABE, GEOFFREY S. MAKIN, & CHRISTOPHER J. MILLS
| title=Velocity of Blood Flow in Normal Human Venae Cavae
| journal=Circulation Research.
| year=1968
| volume=23
| pages=349
| url=http://circres.ahajournals.org/cgi/content/abstract/circresaha;23/3/349
| accessdate=2007-11-14
| pmid=5676450 }}</ref>
*The [[smooth muscle]]s of hollow internal [[viscera|organs]] are moving. The most familiar would be [[peristalsis]] which is where digested [[food]] is forced throughout the [[digestive tract]]. Though different foods travel through the body at rates, an average speed through the human [[small intestine]] is 2.16 m/h or 0.036 m/s.<ref>[http://www.vivo.colostate.edu/hbooks/pathphys/digestion/basics/transit.html Bowen, R.] 2006. Gastrointestinal Transit: How Long Does It Take? Colorado State University.</ref>
*Typically some [[sound]] is audible at any given moment, when the vibration of these sound waves reaches the [[ear drum]] it moves in response and allows the sense of [[Hearing (sense)|hearing]].
*The human [[lymphatic system]] is constantly moving excess [[fluids]], [[lipids]], and immune system related products around the body. The lymph fluid has been found to move through a lymph capillary of the [[skin]] at approximately 0.0000097 m/s.<ref>{{cite journal
| author=M. Fischer, U. K. Franzeck, I. Herrig, U. Costanzo, S. Wen, M. Schiesser, U. Hoffmann and A. Bollinger
| title=Flow velocity of single lymphatic capillaries in human skin
| journal=Am J Physiol Heart Circ Physiology
| year=1996
| volume=270
| pages=H358–H363
| url=http://ajpheart.physiology.org/cgi/content/abstract/270/1/H358
| accessdate=2007-11-14
| pmid=8769772 }}</ref>
=== Cells ===
The [[cells]] of the [[human body]] have many structures which move throughout them.
*[[Cytoplasmic streaming]] is a way which cells move molecular substances throughout the [[cytoplasm]].<ref>[http://www.britannica.com/eb/article-9028448/cytoplasmic-streaming Cytoplasmic Streaming: Encyclopedia Britannica]</ref>
* Various [[motor proteins]] work as [[molecular motors]] within a cell and move along the surface of various cellulars substrate such as [[microtubule]]s. Motor proteins are typically powered by the hydrolysis of ATP and convert chemical energy into mechanical work.<ref>[http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb2/part1/kinesin.htm Microtubule Motors: Rensselaer Polytechnic Institute.]</ref> [[Vesicles]] propelled by motor proteins have been found to have a velocity of approximately 0.00000152 m/s. <ref>{{cite journal
| author=Hill, David; Holzwarth, George; Bonin, Keith
| title=Velocity and Drag Forces on motor-protein-driven Vesicles in Cells
| journal=American Physical Society, The 69th Annual Meeting of the Southeastern
| year=2002
| volume=abstract #EA.002
| url=http://adsabs.harvard.edu/abs/2002APS..SES.EA002H
| accessdate=2007-11-14 }}</ref>
=== Particles ===
*According to the [[laws of thermodynamics]] all [[particle]]s of [[matter]] are in constant random motion as long as the [[temperature]] is above [[absolute zero]]. Thus the [[molecule]]s and [[atom]]s which make you up are vibrating, colliding, and moving. This motion can be detected as temperature; high temperatures (which represent greater [[kinetic energy]] in the particles) feel warmer to humans, whereas lower temperatures feel colder.<ref>[http://www.colorado.edu/UCB/AcademicAffairs/ArtsSciences/physics/PhysicsInitiative/Physics2000/bec/temperature.html Temperature and BEC.] Physics 2000: Colorado State University Physics Department</ref>
=== Subatomic particles ===
*Within each atom the [[electron]]s are speeding around the nucleus so fast that they are not actually in one location, but rather smeared across a region of the [[electron cloud]]. Electrons have a high [[Electron velocity|velocity]], and the larger the nucleus they are orbiting the faster they move. In a hydrogen atom, electrons have been calculated to be orbiting at a speed of approximately 242,000 m/s<ref>[http://www.newton.dep.anl.gov/newton/askasci/1993/physics/PHY112.HTM Ask a scientist archive. Argonne National Laboratory, United States Department of Energy]</ref>
* Inside the [[atomic nucleus]] the [[proton]]s and [[neutron]]s are also probably moving around due the electrical repulsion of the protons and the presence of [[angular momentum]] of both particles.<ref>[http://www.lbl.gov/abc/wallchart/teachersguide/pdf/Chap02.pdf Chapter 2, Nuclear Science- A guide to the nuclear science wall chart. Berkley National Laboratory.]</ref>
== Light ==
{{main|Light}}
{{Refimprove|date=March 2008}}
Light is both a photon and a wave, and moves at 186,000 miles per second (300,000 km per second). It is the fastest moving thing known to man, and, according to Einstein, a limit which nothing can travel faster than. Einstein also claimed that time would "slow down" for whatever was traveling near light speed; so, if a person was moving near light speed, they would age slower than someone who was not. Since light is what humans depend on to see the universe, there are tiny, imperceptible changes in what one observer is seeing compared to another. This is because, of course, that light still has to travel to get to an observer; so, if Observer #2 was twice as far from an object than Observer #1, Observer #2 would see it two times later than Observer #1. This can especially be seen when you look at stars many light-years away: you are actually seeing the past of that star, not what is happening at moment, since the light from that star must travel years and years to reach earth (depending on exactly how far away it was).
==Types==
*[[Simple harmonic motion]] - motion that is constantly being accelerated towards a midpoint (e.g. a swinging [[pendulum]]).
*[[Linear motion]] - motion which follows a straight [[line]]ar path, and whose [[displacement (vector)|displacement]] is exactly the same as its [[trajectory]].
*[[Reciprocation]] (i.e. vibration)
*[[Brownian Motion]] (i.e. the random movement of particles)
*[[Circular motion]] (e.g. the [[orbit]]s of planets)
*[[Rotational motion|Rotary motion]] - a motion about a fixed point ex. the wheel of a bicycle
==See also==
* [[Equation of motion]]
* [[Molecular dynamics]]
* [[Motion perception]]
* [[Newton's laws of motion]]
* [[Trajectory of a projectile]]
* [[Rigid body motion]]
== References ==
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