# Motion (physics)

In physics, motion is a change in position of an object over time. Motion is mathematically described in terms of displacement, distance, velocity, acceleration, time, and speed. Motion of a body is observed by attaching a frame of reference to an observer and measuring the change in position of the body relative to that frame.

If the position of a body is not changing with respect to a given frame of reference (reference point), the body 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. Momentum is a quantity which is used for measuring the motion of an object. An object's momentum is directly related to the object's mass and velocity, and the total momentum of all objects in an isolated 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.[1] Thus, everything in the universe can be considered to be moving.[2]:20–21

Motion applies to objects, bodies, and matter particles, to radiation, radiation fields and radiation particles, and to space, its curvature and space-time. One can also speak of motion of shapes and boundaries. So, the term motion, in general, signifies a continuous change in the configuration of a physical system. For example, one can talk about motion of a wave or about motion of a quantum particle, 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.
Principle of Motion and Principle of Rest are among the six eternal substances in the Jain cosmology

## Laws of motion

In physics, motion is described through two sets of apparently contradictory laws of mechanics. Motions of all large-scale and familiar objects in the universe (such as projectiles, planets, cells, and humans) are described by classical mechanics. Whereas the motion of very small atomic and sub-atomic objects is described by quantum mechanics.

 First law: In an inertial reference frame, an object either remains at rest or continues to move at a constant velocity, unless acted upon by a net force. Second law: In an inertial reference frame, the vector sum of the forces F on an object is equal to the mass m of that object multiplied by the acceleration a of the object: F = ma. Third law: When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.

### 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 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. Newton's three laws are:

1. A body either is at rest or moves with constant velocity, until and unless an outer force is applied to it.
2. An object will travel in one direction only until an outer force changes its direction.
3. Whenever one body exerts a force F onto a second body, (in some cases, which is standing still) the second body exerts the force −F on the first body. F and −F are equal in magnitude and opposite in sense. So, the body which exerts F will go backwards.[3]

Newton's three laws of motion were the first to accurately provide a mathematical model for understanding orbiting bodies in outer space. This explanation unified the motion of celestial bodies and motion of objects on earth.

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

Uniform Motion:

When an object moves with a constant speed at a particular direction at regular intervals of time it's known as the uniform motion. For example: a bike moving in a straight line with a constant speed.

EQUATIONS OF UNIFORM MOTION:

If v = final velocity, u = initial velocity, a = acceleration, t = time, s = displacement, then :

${\displaystyle \mathbf {v} =\mathbf {u} +\mathbf {a} \mathbf {t} }$
${\displaystyle \mathbf {v} ^{2}=\mathbf {u} ^{2}+2\mathbf {a} \mathbf {s} }$
${\displaystyle \mathbf {s} =\mathbf {u} \mathbf {t} +{\frac {\mathbf {a} \mathbf {t} ^{2}}{2}}}$

### Quantum mechanics

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

In classical mechanics, accurate measurements and predictions of the state of objects can be calculated, such as location and velocity. In the quantum mechanics, due to the Heisenberg uncertainty principle, the complete state of a subatomic particle, such as its location and velocity, cannot be simultaneously determined.[citation needed]

In addition to describing the motion of atomic level phenomena, 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.[citation needed]

Other Languages
Afrikaans: Beweging
Alemannisch: Bewegung (Physik)
العربية: حركة (فيزياء)
অসমীয়া: চলন
asturianu: Movimientu
azərbaycanca: Mexaniki hərəkət
বাংলা: গতি
Bân-lâm-gú: Tín-tāng
беларуская: Механічны рух
беларуская (тарашкевіца)‎: Мэханічны рух
български: Движение
bosanski: Kretanje
català: Moviment
Cymraeg: Mudiant
eesti: Liikumine
Ελληνικά: Κίνηση
euskara: Higidura
فارسی: حرکت
galego: Movemento
हिन्दी: गति (भौतिकी)
hrvatski: Gibanje
Ido: Movo
Bahasa Indonesia: Gerak
italiano: Moto (fisica)
ಕನ್ನಡ: ಚಲನೆ
македонски: Движење (физика)
മലയാളം: ചലനം
मराठी: गती
Bahasa Melayu: Pergerakan (fizik)
монгол: Хөдөлгөөн
norsk nynorsk: Rørsle i fysikk
português: Movimento
Runa Simi: Kuyuy
sardu: Movimentu
sicilianu: Motu (fìsica)
Simple English: Movement
slovenčina: Mechanický pohyb
slovenščina: Gibanje
کوردی: جووڵە
српски / srpski: Кретање
srpskohrvatski / српскохрватски: Gibanje
Basa Sunda: Gerak
Tagalog: Mosyon
తెలుగు: చలనం
тоҷикӣ: Ҳаракат
ತುಳು: ಚಲನೆ
Türkçe: Hareket (fizik)
Türkmençe: Mehaniki hereket
українська: Рух (механіка)
Tiếng Việt: Chuyển động
ייִדיש: באוועגונג
Yorùbá: Ìmúrìn