In physics Physics is a natural science that involves the study of matter and its motion through space-time, as well as all applicable concepts, such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves, motion is change of location or position A position, location, or radius vector is a vector which represents the position of an object in space in relation to an arbitrary reference point. The concept applies to two- or three-dimensional space. The term is also used as a means of deriving displacement by the spatial comparison of two or more position vectors and are usually 2- or, of an object with respect to time. Change in motion is the result of an applied force In physics, a force is any influence that causes a free body to undergo an acceleration. Force can also be described by intuitive concepts such as a push or pull that can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform. A force has both magnitude and direction, making it a. Motion is typically described in terms of velocity In physics, velocity is the rate of change of position. It is a vector physical quantity; both magnitude and direction are required to define it. The scalar absolute value of velocity is speed, a quantity that is measured in meters per second (m/s or ms−1) when using the SI (metric) system also seen as speed, acceleration In physics, and more specifically kinematics, acceleration is the change in velocity over time. Because velocity is a vector, it can change in two ways: a change in magnitude and/or a change in direction. In one dimension, i.e. a line, acceleration is the rate at which something speeds up. However, as a vector quantity, acceleration is also the, displacement A displacement is the shortest distance from the initial and final positions of a point P. Thus, it is the length of an imaginary straight path, typically distinct from the path actually travelled by P. A displacement vector represents the length and direction of that imaginary straight path, and time Time is "a nonspatial continuum in which events occur in apparently irreversible succession from the past through the present to the future." It is used to sequence events, to quantify the durations of events and the intervals between them, and to quantify and measure the motions of objects and other changes. Time is quantified in.^[1] An object's velocity cannot change unless it is acted upon by a force In physics, a force is any influence that causes a free body to undergo an acceleration. Force can also be described by intuitive concepts such as a push or pull that can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform. A force has both magnitude and direction, making it a, as described by Newton's first law Newton's laws of motion are three physical laws that form the basis for classical mechanics. They have been expressed in several different ways over nearly three centuries, and can be summarised as follows: also known as Inertia Inertia is the resistance of any physical object to a change in its state of motion. It is represented numerically by an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to describe the motion of matter and how it is affected by applied forces. Inertia comes from the Latin word, ". An object's momentum In classical mechanics, momentum is the product of the mass and velocity of an object (p = mv). In relativistic mechanics, this quantity is multiplied by the Lorentz factor. Momentum is sometimes referred to as linear momentum to distinguish it from the related subject of angular momentum. Linear momentum is a vector quantity, since it has a is directly related to the object's mass In physics, mass commonly refers to any of three properties of matter, which have been shown experimentally to be equivalent: Inertial mass, active gravitational mass and passive gravitational mass. In everyday usage, mass is often taken to mean weight, but in scientific use, they refer to different properties and velocity In physics, velocity is the rate of change of position. It is a vector physical quantity; both magnitude and direction are required to define it. The scalar absolute value of velocity is speed, a quantity that is measured in meters per second (m/s or ms−1) when using the SI (metric) system, and the total momentum of all objects in a closed system In computing a closed system refers to software which the specifications and detail of implementation are kept secret, as opposed to open source systems (one not affected by external forces) does not change with time, as described by the law of conservation of momentum In classical mechanics, momentum is the product of the mass and velocity of an object (p = mv). In relativistic mechanics, this quantity is multiplied by the Lorentz factor. Momentum is sometimes referred to as linear momentum to distinguish it from the related subject of angular momentum. Linear momentum is a vector quantity, since it has a.

A body which does not move is said to be at rest, motionless, immobile, stationary, or to have constant (time-invariant A time-invariant system is one whose output does not depend explicitly on time. That is, treating time as the independent variable, it is an autonomous system) position.

Motion is always observed and measured relative to a frame of reference A frame of reference in physics, may refer to a coordinate system or set of axes within which to measure the position, orientation, and other properties of objects in it, or it may refer to an observational reference frame tied to the state of motion of an observer. It may also refer to both an observational reference frame and an attached. As there is no absolute reference frame, absolute motion cannot be determined; this is emphasised by the term relative motion.^[2] A body which is motionless relative to a given reference frame, moves relative to infinitely many other frames. Thus, everything in the universe is moving.^[3]

More generally, the term motion signifies any spatial and/or temporal change in a physical system. For example, one can talk about motion of a wave or a quantum particle (or any other field In physics, a field is a physical quantity associated to each point of spacetime. A field can be classified as a scalar field, a vector field, a tensor field,or a spinor field according to whether the value of the field at each point is a scalar, a vector, a spinor or, more generally, a tensor, respectively. For example, the Newtonian) where the concept location does not apply.

Laws of Motion

In physics, motion in the universe is described through two sets of apparently contradictory laws A scientific law or scientific principle is a concise verbal or mathematical statement of a relation that expresses a fundamental principle of science, like Newton's law of universal gravitation. A scientific law must always apply under the same conditions, and implies a causal relationship between its elements. The law must be confirmed and of mechanics Mechanics is the branch of physics concerned with the behavior of physical bodies when subjected to forces or displacements, and the subsequent effects of the bodies on their environment. The discipline has its roots in several ancient civilizations (see History of classical mechanics and Timeline of classical mechanics). During the early modern. Motions of all large scale and familiar objects in the universe (such as projectiles A projectile is any object projected into space by the exertion of a force. Although a thrown baseball is technically a projectile too, the term more often refers to a weapon., planets A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.[a], cells The cell is the functional basic unit of life. It was discovered by Robert Hooke and is the functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. Some organisms, such as most bacteria, are unicellular . Other organisms, such as humans,, and humans Humans are a species of animal known taxonomically as Homo sapiens , and are the only extant member of the Homo genus of bipedal primates in Hominidae, the great ape family. However, in some cases "human" is used to refer to any member of the genus Homo) are described by classical mechanics In the fields of physics, classical mechanics is one of the two major sub-fields of study in the science of mechanics, which is concerned with the set of physical laws governing and mathematically describing the motions of bodies and aggregates of bodies geometrically distributed within a certain boundary under the action of a system of forces. Whereas the motion of very small atomic The name Atom applies to a pair of related standards. The Atom Syndication Format is an XML language used for web feeds, while the Atom Publishing Protocol is a simple HTTP-based protocol for creating and updating web resources and sub-atomic In physics, subatomic particles are the small particles composing nucleons and atoms. There are two types of subatomic particles: elementary particles, which are not made of other particles, and composite particles. Particle physics and nuclear physics study these particles and how they interact sized objects is described by quantum mechanics Quantum mechanics or quantum physics or quantum theory, is a branch of physics that provides a mathematical description of much of the particle-like and wave-like behavior and interactions of energy and matter that depart from classical mechanics at the atomic and subatomic scales. In advanced topics of QM, some of these behaviors are macroscopic.

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, stars, 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 fundamentally based on Newton's Laws of Motion. These laws describe the relationship between the forces acting on a body and the motion of that body. They were first compiled by Sir Isaac Newton in his work Philosophiæ Naturalis Principia Mathematica, first published on July 5, 1687. His three laws are:

1. In the absence of a net external force, a body either is at rest or moves with constant velocity.
2. The net external force on a body is equal to the mass of that body times its acceleration; F = ma. Alternatively, force is proportional to the time derivative of momentum.
3. Whenever a first body exerts a force F on a second body, the second body exerts a force −F on the first body. F and −F are equal in magnitude and opposite in direction.^[4]

Newton's three laws of motion, along with his law of universal gravitation, explain Kepler's laws of planetary motion, which were the first to accurately provide a mathematical model or understanding orbiting bodies in outer space. This explanation unified the motion of celestial bodies and motion of objects on earth.

Classical mechanics was later further enhanced by Albert Einstein's special relativity and general relativity. Special relativity explains the motion of objects with a high velocity, approaching the speed of light; general relativity is employed to handle gravitation motion at a deeper level.

Quantum mechanics

Quantum mechanics is a set of principles describing physical reality at the atomic level of matter (molecules and atoms) and the subatomic (electrons, protons, and even smaller particles). These descriptions include the simultaneous wave-like and particle-like behavior of both matter and radiation energy, this described in the wave–particle duality.

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).

In addition to describing the motion of atomic level phenomenon, quantum mechanics is useful in understanding some large scale phenomenon such as superfluidity, superconductivity, and biological systems, including the function of smell receptors and the structures of proteins.

List of "imperceptible" human motions

Humans, like all things in the universe are in constant motion,^[5] 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.^[6] The smaller scales of these motions are too small for humans to sense.

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.^[7]

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.^[8]

Solar System

• The Milky Way is rotating around its 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 (or about a half-million mi/h).^[9]

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 (or 1040 mi/h).^[10]
• 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 (or 67,000 mi/h).^[11]

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.^[12][13] 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^[14] (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.^[15] 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.^[16]
• 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 or 0.036 m/s.^[17]
• 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.^[18]

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.^[19]
• Various motor proteins work as molecular motors within a cell and move along the surface of various cellular substrates such as microtubules. Motor proteins are typically powered by the hydrolysis of adenosine triphosphate, (ATP), and convert chemical energy into mechanical work.^[20] Vesicles propelled by motor proteins have been found to have a velocity of approximately 0.00000152 m/s.^[21]

Particles

• According to the laws of thermodynamics all particles of matter 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; high temperatures (which represent greater kinetic energy in the particles) feel warmer to humans, whereas lower temperatures feel colder.^[22]

Subatomic particles

• Within each atom the electrons 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 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 2,420,000 m/s^[23]
• Inside the atomic nucleus the protons and neutrons are also probably moving around due the electrical repulsion of the protons and the presence of angular momentum of both particles.^[24]

Light

Light propagates at 299,792,458 m/s (about 186,282.397 mi/s).

Types

• Simple harmonic motion – (e.g. pendulum).
• Linear motion – motion which follows a straight linear path, and whose displacement is exactly the same as its trajectory.
• Reciprocating (i.e. vibration)
• Brownian Motion (i.e. the random movement of particles)
• Circular motion (e.g. the orbits of planets)
• 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

1. ^ Nave, R. 2005. Motion. HyperPhysics. Georgia State University
2. ^ Wåhlin, L. 1997. "THE DEADBEAT UNIVERSE", Chapter 9. Colutron Research Corporation ISBN 0 933407 03 3
3. ^ De Grasse Tyson, N., Liu, C., & Irion, R. 2000. One Universe: At home in the cosmos. p.20–21. Joseph Henry Press. ISBN 0-309-06488-0
4. ^ Newton's "Axioms or Laws of Motion" can be found in the "Principia" on page 19 of volume 1 of the 1729 translation.
5. ^ De Grasse Tyson, N., Liu, C., & Irion, R. 2000. One Universe: At home in the cosmos. p.8–9. Joseph Henry Press. ISBN 0-309-06488-0
6. ^ 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
7. ^ Hubble, Edwin, "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 (Full article, PDF)
8. ^ 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. (1993). "Dipole Anisotropy in the COBE Differential Microwave Radiometers First-Year Sky Maps". Astrophysical Journal 419: 1. doi:10.1086/173453. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1993ApJ...419....1K. Retrieved 2007-05-10.
9. ^ Imamura, Jim (August 10, 2006). "Mass of the Milky Way Galaxy". University of Oregon. http://zebu.uoregon.edu/~imamura/123/lecture-2/mass.html. Retrieved 2007-05-10.
10. ^ Ask and Astrophysicist. NASA Goodard Space Flight Center.
11. ^ Williams, David R. (September 1, 2004). "Earth Fact Sheet". NASA. http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html. Retrieved 2007-03-17.
12. ^ Staff. "GPS Time Series". NASA JPL. http://sideshow.jpl.nasa.gov/mbh/series.html. Retrieved 2007-04-02.
13. ^ Huang, Zhen Shao. "Speed of the Continental Plates". The Physics Factbook. http://hypertextbook.com/facts/ZhenHuang.shtml. Retrieved 2007-11-09.
14. ^ Meschede, M.; Udo Barckhausen, U. (November 20, 2000). "Plate Tectonic Evolution of the Cocos-Nazca Spreading Center". Proceedings of the Ocean Drilling Program. Texas A&M University. http://www-odp.tamu.edu/publications/170_SR/chap_07/chap_07.htm. Retrieved 2007-04-02.
15. ^ Penny, P. 2003. Hemodynamic: Blood Velocity
16. ^ LEWIS WEXLER, DEREK H. BERGEL, IVOR T. GABE, GEOFFREY S. MAKIN, & CHRISTOPHER J. MILLS (1 September 1968). "Velocity of Blood Flow in Normal Human Venae Cavae". Circulation Research. 23 (3): 349. PMID 5676450. http://circres.ahajournals.org/cgi/content/abstract/circresaha;23/3/349. Retrieved 2007-11-14.
17. ^ Bowen, R. 2006. Gastrointestinal Transit: How Long Does It Take? Colorado State University.
18. ^ M. Fischer, U. K. Franzeck, I. Herrig, U. Costanzo, S. Wen, M. Schiesser, U. Hoffmann and A. Bollinger (1 January 1996). "Flow velocity of single lymphatic capillaries in human skin". Am J Physiol Heart Circ Physiology 270 (1): H358–H363. PMID 8769772. http://ajpheart.physiology.org/cgi/content/abstract/270/1/H358. Retrieved 2007-11-14.
19. ^ Cytoplasmic Streaming: Encyclopedia Britannica
20. ^ Microtubule Motors: Rensselaer Polytechnic Institute.
21. ^ 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. http://adsabs.harvard.edu/abs/2002APS..SES.EA002H. Retrieved 2007-11-14.
22. ^ Temperature and BEC. Physics 2000: Colorado State University Physics Department
23. ^ Ask a scientist archive. Argonne National Laboratory, United States Department of Energy
24. ^ Chapter 2, Nuclear Science- A guide to the nuclear science wall chart. Berkley National Laboratory.

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