motion
In physics, motion is
a change in position of an object over time. Motion is typically 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, 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 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. Thus,
everything in the universe can be considered to be moving.
More generally,
motion is a concept that 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.
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.
List of "imperceptible" human motions
Humans, like all
known things in the universe, are in constant motion,
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.[4]
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.[5]
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 582 km/s.[6][not in citation given]
Sun and solar system
- The Milky Way is rotating around its dense galactic 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. 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).
- 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).
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.[10][11] 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 (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.
- 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).
- 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.
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.
- 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 hydrolysis of adenosine triphosphate (ATP), and convert chemical energy into mechanical work. Vesicles propelled by motor proteins have been found to have a velocity of approximately 0.00000152 m/s.
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.
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.
- 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.
Light
Main : 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 also 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. The speed of light is
the limit speed for physical systems.
In addition, the
speed of light is an invariant quantity: it has the same value, irrespective of
the position or speed of the observer. This property makes the speed of light c
the natural measurement unit for speed.
Types of motion
- Simple harmonic motion – (e.g., that of a pendulum).
- Anharmonic motion
- Periodic motion
- Linear motion – motion which follows a straight linear path, and whose displacement is exactly the same as its trajectory.
- Reciprocal motion (e.g. vibration)
- Random motion (e.g. 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. (e.g. Ferris wheel).
- Curvilinear motion – It is defined as the motion along a curved path that may be planar or in three dimensions.
- Rotational motion
- Rolling motion - (as of the wheel of a bicycle)
- Oscillation
- vibratory motion
- Combination (or simultaneous) motions - Combination of two or more above listed motions
- Projectile motion - uniform horizontal motion + vertical accelerated motion
- Half projectile motion
- circular motion(this is a motion that move in a round of body)(e.g the moon and the earth)
There are
so many types of motion but for the cause of this study for senior secondary
school one (SS1). Our study will be limited to the four main types of motion.
Transnational motion results in a change of location. This category may
seem ridiculous at first as motion implies a change in location, but an object
can be moving and yet not go anywhere. I get up in the morning and go to work
(an obvious change in location), but by evening I'm back at home — back in the
very same bed where I started the day. Is this transnational motion? Well, it
depends. If the problem at hand is to determine how far I travel in a day, then
there are two possible answers: either I've gone to work and back (22 km
each way for a total of 44 km) or I've gone nowhere (22 km each way
for a total of 0 km). The first answer invokes transitional motion while
the second invokes oscillatory motion.
Oscillatory motion is repetitive and fluctuates between two locations.
In the previous example of going from home to work to home to work I am moving,
but in the end I haven't gone anywhere. This second type of motion is seen in
pendulums (like those found in grandfather clocks), vibrating strings (a guitar
string moves but goes nowhere), and drawers (open, close, open, close — all
that motion and nothing to show for it). Oscillatory motion is interesting in
that it often takes a fixed amount of time for an oscillation to occur. This
kind of motion is said to be periodic and the time
for one complete oscillation (or one cycle) is called a period.
Periodic motion is important in the study of sound, light, and other waves.
Large chunks of physics are devoted to this kind repetitive motion. Doing the
same thing over and over and going nowhere is pretty important; which brings us
to our next type of motion.
Rotational motion occurs when an object spins. The earth is in a
constant state of motion, but where does that motion take it? Every twenty-four
hours it makes one complete rotation about its axis. (Actually, it's a bit less
than that, but let's not get bogged down in details.) The sun does the same
thing, but in about twenty-four days. So do all the planets, asteroids, and
comets; each with its own period. (Note that rotational motion too is often
periodic.) On a more mundane level, bocce balls, CDs, and wheels also rotate. The best example is our fan.
Random motion occurs for one of two reasons.
Some motion is
predictable in theory but unpredictable in practice, which makes it appear
random. For example, a single molecule in a gas will move freely until it
strikes another molecule or one of the walls containing it. The direction the
molecule travels after a collision like this is completely predictable
according to current theories of classical mechanics.
Every measurement has uncertainty associated with it. Every calculation made
using the results of a measurement will carry that uncertainty along. Now
imagine that you are trying to predict the motion of a billion gas atoms in a
container. (That's a small amount, by the way.) After measuring the position
and velocity of each one as accurately as possible, you enter the data into a
monstrous computer and let it do the calculations for you. Since the
measurements associated with each molecule are a little off, the first round of
computation will be a little wrong. Those wrong numbers will then be used in
the next round of calculation and the results will be a little more wrong.
After a billion calculations, the compounded error would render the results
useless. The molecule could be anywhere within the container. This type of
randomness is called chaos.
Some motion is
unpredictable in theory and is truly random. For example, the motion of the
electron in an atom is fundamentally unpredictable because of a weird
conspiracy of nature described by quantum mechanics.
The harder you try to locate the electron, the less you know about its
velocity. The harder you try to measure its velocity, the less you know about
its location. This is fundamental quality of small objects like electrons and
there is no way around it. Although the electron is often said to
"orbit" the nucleus of an atom, strictly speaking, this isn't true.
The probability of finding the electron at any particular point in space is
predictable, but how it got from the first place you observed it to the second
is actually a meaningless question. There is no name for this kind of motion
because the concept of motion doesn't even apply.
