Motion
(physics)
From Wikipedia, the free encyclopedia
In physics,
motion is a
change in position
of an object with respect to time also on its reference point.
Motion is typically described in terms of displacement,
distance
(scalar), velocity,
acceleration,
time and speed.[1]
Motion is observed by attaching a frame
of reference to a body and measuring its change in position
relative to that frame.
If the position of a body is not changing with
the time with respect to a given frame of reference 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 by Newton's
first law. Momentum is a quantity which is used for measuring
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. The study of motion deals with (1)
The study of motion of solids (mechanics). (2) study of motion of
fluids (fluid
mechanics)
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
[clarification
needed].[3]:20–21
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.
Laws of motion
Main article: Mechanics
In physics, motion in the universe 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.
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:
A body
either is at rest or moves with constant velocity, until and unless
an outer force is applied to it.
An object will travel in one
direction only until an outer force changes its direction.
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.[4]
Newton's three laws of motion, along with his Newton's
law of motion, which 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 later further enhanced by Albert
Einstein's special
relativity and general
relativity. Motion of objects with a high velocity,
approaching the speed
of light; general
relativity is employed to handle gravitational
motion at a deeper level.
Quantum mechanics
Main article: 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 is 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]
List of "imperceptible" human motions
Humans,
like all known things in the universe, are in constant motion,[3]:8–9
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.[5]
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.[6]
Galaxy
The Milky
Way Galaxy, is moving through space.
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.[7]
Sun
Solar System
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).[9]
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).[10]
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.[11][12]
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[13]
(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.
Though considerable variation exists, and peak flows in the venae
cavae have been found between 0.1 m/s and 0.45 m/s.[14]
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).[15]
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.[16]
Cells
The cells
of the human body
have many structures which move throughout them.
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; 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.[20]
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.[21]
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.[22]
Light
Main article: Speed
of light
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 (or c) 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.
Types of motion
See also