[[Image:Leaving Yongsan Station.jpg|300px|thumb|right|Motion involves a change in position, such as in this perspective of rapidly leaving [[Yongsan Station]].]]
[[Image:Leaving Yongsan Station.jpg|300px|thumb|right|Motion involves a change in position, such as in this perspective of rapidly leaving [[Yongsan Station]].]]
==Laws of Motion==
Gamgam style yo oy Nicolas bob bob
{{main|Mechanics}}
In physics, motion in the universe is described through two sets of apparently contradictory [[scientific law|laws]] of [[mechanics]]. Motions of all large scale and familiar objects in the universe (such as [[projectile]]s, [[planet]]s, [[Cell (biology)|cell]]s, and [[human]]s) are described by [[classical mechanics]]. Whereas the motion of very small [[atom]]ic and [[subatomic particle|sub-atomic]] objects is described by [[quantum mechanic]]s.
===Classical mechanics===
{{main|Classical mechanics}}
{{Classical mechanics}}
{{Classical mechanics}}
Classical mechanics is used for describing the motion of [[macroscopic]] objects, from [[projectiles]] to parts of [[machinery]], as well as [[astronomical objects]], such as [[spacecraft]], [[planets]], [[star]]s, and [[galaxies]]. It produces very accurate results within these domains, and is one of the oldest and largest subjects in [[science]], [[engineering]], and [[technology]].
Classical mechanics is used for describing the motion of [[macroscopic]] objects, from [[projectiles]] to parts of [[machinery]], as well as [[astronomical objects]], such as [[spacecraft]], [[planets]], [[star]]s, and [[galaxies]]. It produces very accurate results within these domains, and is one of the oldest and largest subjects in [[science]], [[engineering]], and [[technology]].
Revisionasof00:59,23January2013
Inphysics, motion is a change in position of an object with respect to time and its reference point. Motion is typically described in terms of velocity, acceleration, displacement, and time.[1] Motion is observed by attaching a frame of reference to a body and measuring its change in position relative to another reference frame.
A body which does not move is said to be at rest, motionless, immobile, stationary, or to have constant (time-invariant) position. An object's motion cannot change unless it is acted upon by a force, as described by Newton's first law. An object's momentum is directly related to the object's mass and velocity, and the total momentum of all objects in a closed system (one not affected by external forces) does not change with time, as described by the law of conservation of momentum.
As there is no absolute frame of reference, absolute motion cannot be determined.[2] Thus, everything in the universe can be considered to be moving.[3]
More generally, the term motion signifies a continuous change in the configuration of a physical system. For example, one can talk about motion of a wave or a quantum particle (or any other field) where the configuration consists of probabilities of occupying specific positions.
Motion involves a change in position, such as in this perspective of rapidly leaving Yongsan Station.
In the absence of a net external force, a body either is at rest or moves with constant velocity.
The net external force on a body is equal to the mass of that body times its acceleration; F = ma. Alternatively, the acceleration is directly proportional to the force causing it, and inversely proportional to the mass.
Whenever one body exerts a force F onto a second body, the second body exerts the force −F on the first body. F and −F are equal in magnitude and opposite in sense.[4]
In contrast to classical mechanics, where accurate measurements and predictions can be calculated about location and velocity, in the quantum mechanics of a subatomic particle, one can never specify its state, such as its simultaneous location and velocity, with complete certainty (this is called the Heisenberg uncertainty principle).
Kinematics applies geometry to the analysis of movement, or motion, of a mechanical system.
Rest and motion is a very relative term as far as the frames of reference is concerned. So, while proceeding with any of the problems in kinematics one should be very careful about the frame of reference.
[5] The rotation and sliding movement central a mechanical system is modeled mathematically as Euclidean, or rigid, transformations. The set of rigid transformations in three dimensional space forms a Lie group, denoted as SE(3).
Planar motion
While all motion in a mechanical system occurs in three dimensional space, planar motion can be analyzed using plane geometry, if all point trajectories are parallel to a plane. In this case the system is called a planar mechanism (or robot). The kinematic analysis of planar mechanisms uses the subset of SE(3) consisting of planar rotations and translations, denoted SE(2).
The group SE(2) is three dimensional, which means that every position of a body in the plane is defined by three parameters. The parameters are often the x and y coordinates of the origin of a coordinate frame in M measured from the origin of a coordinate frame in F, and the angle measured from the x-axis in F to the x-axis in M. This is described saying a body in the plane has three degrees-of-freedom. SE(2) is the configuration space for a planar body, and a planar motion is a curve in this space.
Spherical motion
It is possible to construct a mechanical system such that the point trajectories in all components lie in concentric spherical shells around a fixed point. An example is the gimbaledgyroscope. These devices are called spherical mechanisms.[6] Spherical mechanisms are constructed by connecting links with hinged joints such that the axes of each hinge passes through the same point. This point becomes center of the concentric spherical shells. The movement of these mechanisms is characterized by the group SO(3) of rotations in three dimensional space. Other examples of spherical mechanisms are the automotive differential and the robotic wrist.
The rotation group SO(3) is three dimensional. An example of the three parameters that specify a spatial rotation are the roll, pitch and yaw angles used to define the orientation of an aircraft. SO(3) is the configuration space for a rotating body, and a spherical motion is a curve in this space.
Spatial motion
Amechanical system in which a body moves through a general spatial movement is called a spatial mechanism. An example is the RSSR linkage, which can be viewed as a four-bar linkage in which the hinged joints of the coupler link are replaced by rod ends, also called spherical joints or ball joints. The rod ends allow the input and output cranks of the RSSR linkage to be misaligned to the point that they lie in different planes, which causes the coupler link to move in a general spatial movement. Robot arms, Stewart platforms, and humanoid robotic systems are also examples of spatial mechanisms.
Select this link for an animation of Bennett's linkage, which is a spatial mechanism constructed from four hinged joints.
The group SE(3) is six dimensional, which means the position of a body in space is defined by six parameters. Three of the parameters define the origin of the moving reference frame relative to the fixed frame. Three other parameters define the orientation of the moving frame relative to the fixed frame. SE(3) is the configuration space for a body moving in space, and a spatial motion is a curve in this space.
List of "imperceptible" human motions
Humans, like all known things in the universe, are in constant motion,[7] however, aside from obvious movements of the various external body parts and locomotion, humans are in motion in a variety of ways which are more difficult to 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 frame of reference which would allow individuals to easily see that they are moving.[8] The smaller scales of these motions are too small for humanstosense.
Universe
Spacetime (the fabric of the universe) is actually 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.[9]
Galaxy
The Milky Way Galaxy, is hurtling through space at an incredible speed. 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.[10]
Sun
The Milky Way is rotating around its densegalactic center, thus the sun 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 (about half-million mi/h).[11]
Solar System
All planets and their moons move with the sun. Thus the solar system is moving.
Earth
The Earth is rotating or spinning around its axis, this is evidenced by day and night, at the equator the earth has an eastward velocity of 0.4651 km/s (1040 mi/h).[12]
The Earth is orbiting 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 (67,000 mi/h).[13]
Continents
The Theory of Plate tectonics tells us that the continents are drifting on convection currents within the mantle causing them to move across the surface of the planet at the slow speed of approximately 1 inch (2.54 cm) per year.[14][15] 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[16] (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.[17] Though considerable variation exists, and peak flows in the venae cavae have been found between 0.1 m/s and 0.45 m/s.[18]
The smooth muscles of hollow internal 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 (0.036 m/s).[19]
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.
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.[20]
Cells
The cells of the human body have many structures which move throughout them.
Various motor proteins work as molecular motors within a cell and move along the surface of various cellular substrates such as microtubuless. Motor proteins are typically powered by the hydrolysisofadenosine triphosphate (ATP), and convert chemical energy into mechanical work.[22]Vesicles propelled by motor proteins have been found to have a velocity of approximately 0.00000152 m/s.[23]
Particles
According to the laws of thermodynamics all particlesofmatter are in constant random motion as long as the temperature is above absolute zero. Thus the molecules and atoms which make up the human body are vibrating, colliding, and moving. This motion can be detected as temperature; higher temperatures, which represent greater kinetic energy in the particles, feel warm to humans whom sense the thermal energy transferring from the object being touched to their nerves. Similarly, when lower temperature objects are touched, the senses perceive the transfer of heat away from the body as feeling cold.[24]
Subatomic particles
Within each atom, electrons exist in an area around the nucleus. This area is called the electron cloud. According to Bohr's model of the atom, electrons have a high velocity, and the larger the nucleus they are orbiting the faster they would need to move. If electrons 'move' about the electron cloud in strict paths the same way planets orbit the sun, then electrons would be required to do so at speeds which far exceed the speed of light. However, there is no reason that one must confine one's self to this strict conceptualization, that electrons move in paths the same way macroscopic objects do. Rather one can conceptualize electrons to be 'particles' that capriciously exist within the bounds of the electron cloud.[25]
Light propagates at 299,792,458 m/s, often approximated as 300,000 kilometres per second or 186,000 miles per second. The speed of light (orc) is the speed of all massless particles and associated fields in a vacuum, and it is the upper limit on the speed at which energy, matter, and information can travel.
^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
^LEWIS WEXLER, DEREK H. BERGEL, IVOR T. GABE, GEOFFREY S. MAKIN, & CHRISTOPHER J. MILLS (1 September 1968GGHKHJ,H,kamnalaa mancha haru
khatam). "Velocity of Blood Flow in Normal Human Venae Cavae". Circulation Research. 23 (3): 349–59. PMID5676450. Retrieved 2007-11-14. {{cite journal}}: Check date values in: |date= (help); line feed character in |date= at position 46 (help)CS1 maint: multiple names: authors list (link)
^Bowen, R. 2006. Gastrointestinal Transit: How Long Does It Take? Colorado State University.
^Hill, David; Holzwarth, George; Bonin, Keith (2002). "Velocity and Drag Forces on motor-protein-driven Vesicles in Cells". American Physical Society, the 69th Annual Meeting of the Southeastern. abstract. #EA.002. Bibcode:2002APS..SES.EA002H.{{cite journal}}: CS1 maint: multiple names: authors list (link)
