Motion (physics)

Articles on aviation - Aerospace Engineering

Motion (physics)

By Wikipedia,
the free encyclopedia,

http://en.wikipedia.org/wiki/Motion_(physics)

Motion involves change in position, such as in this perspective of rapidly leaving Yongsan Station

In physics, motion means a change in the location of a body. Change in motion is the result of applied force. Motion is typically described in terms of velocity, acceleration, displacement, and time. An object's velocity cannot change unless it is acted upon by a force, as described by Newton's first law also known as Inertia. 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.

A body which does not move is said to be at rest, motionless, immobile, stationary, or to have constant (time-invariant) position.

Motion is always observed and measured relative to a frame of reference. As there is no absolute reference frame, absolute motion cannot be determined; this is emphasised by the term relative motion. 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.

List of "imperceptible" human motions

Humans, like all 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. 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.

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.

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.

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).
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).

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. 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 to range 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 or 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 cellulars substrate such as microtubules. 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 you up 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.

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
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

Light propagates at 299,792,458 m/s (about 186,282.397 mi/s). According to the theory of relativity, nothing can move faster than the speed of light.

Types

Simple harmonic motion - pendulum).
Linear motion - motion which follows a straight linear path, and whose displacement is exactly the same as its trajectory.
Reciprocation (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