mechanics - Significance, Types of Mechanical Bodies, Sub-disciplines in mechanics, Professional Organizations

The study of the motion of objects as a result of the forces acting on them. Motion in a straight line is called linear or rectilinear motion, and is described using mass m, velocity v, acceleration a, momentum p, and force F; rotational motion is described using moment of inertia I, angular velocity ?, angular acceleration ?, angular momentum L, and torque ?. Quantum mechanics governs objects the size of atoms (10^?10 m) or less. Classical mechanics corresponds to all other aspects of mechanics, and includes Newtonian mechanics, celestial mechanics (the motion of stars and planets), general relativity, fluid mechanics, and relativistic mechanics (for objects moving at high velocity).

Significance

Mechanics is the original discipline of physics, dealing with the macroscopic world that humans perceive.

Mechanics also constitutes a central part of technology, the application of physical knowledge for humanly defined purposes. Important aspects of the fields of mechanical engineering, aerospace engineering, civil engineering, structural engineering, materials engineering, biomedical engineering and biomechanics were spawned from the study of mechanics. Quantum

The major division of the mechanics discipline separates classical mechanics from quantum mechanics.

Historically, classical mechanics came first, while quantum mechanics is a comparatively recent invention. Classical mechanics is older than written history, while quantum mechanics didn't appear until 1900.

Quantum mechanics is, formally at least, of the widest scope, and can be seen as encompassing classical mechanics, as a sub-discipline which applies under certain restricted circumstances. While it is true that historically quantum mechanics has been seen as having superseded classical mechanics, this is only true on the hypothetical or foundational level. For practical problems, classical mechanics is able to solve problems which are unmanageably difficult in quantum mechanics and hence remains useful and well used. classical reformation, Einstein's general and special theories of relativity have expanded the scope of mechanics beyond the mechanics of Newton and Galileo, and made small corrections to them. Relativistic corrections were also needed for quantum mechanics, although relativity is categorized as a classical theory. Just as one could, in the loosest possible sense, characterize classical mechanics as dealing with "large" bodies (such as engine parts), and quantum mechanics with "small" ones (such as particles), it could be said that relativistic mechanics deals with "fast" bodies, and non-relativistic mechanics with "slow" ones. This means that all mechanics, whether classical or quantum, potentially needs to be described relativistically.

Types of Mechanical Bodies

Thus the often-used term body needs to stand for a wide assortment of objects, including particles, projectiles, spacecraft, stars, parts of machinery, parts of solids, parts of fluids (gases and liquids), etc.

Other distinctions between the various sub-disciplines of mechanics, concern the nature of the bodies being described. Particles are bodies with little (known) internal structure, treated as mathematical points in classical mechanics.

For instance: The motion of a spacecraft, regarding its orbit and attitude (rotation), is described by the relativistic theory of classical mechanics. While analogous motions of an atomic nucleus are described by quantum mechanics.

Sub-disciplines in mechanics

The following are two lists of various subjects that are studied in mechanics.

Note that there is also the "theory of fields" which constitutes a separate discipline in physics, formally treated as distinct from mechanics, whether classical fields or quantum fields. In fact, in quantum mechanics, particles themselves are fields, as described theoretically by the wave function.

Classical mechanics

The following are described as forming Classical mechanics:

Newtonian mechanics, the original theory of motion (kinematics) and forces (dynamics) Lagrangian mechanics, a theoretical formalism Hamiltonian mechanics, another theoretical formalism Celestial mechanics, the motion of stars, galaxies, etc. Statics, semi-rigid bodies in mechanical equilibrium Fluid mechanics, the motion of fluids Continuum mechanics, mechanics of continua (both solid and fluid) Hydraulics, fluids in equilibrium Applied / Engineering mechanics Biomechanics, solids, fluids, etc. in biology Statistical mechanics, large assemblies of particles Relativistic or Einsteinian mechanics, universal gravitation

Quantum mechanics

The following are categorized as being part of Quantum mechanics:

Particle physics, the motion, structure, and reactions of particles Nuclear physics, the motion, structure, and reactions of nuclei Condensed matter physics, quantum gases, solids, liquids, etc. Quantum statistical mechanics, large assemblies of particles

Professional Organizations

Applied Mechanics Division, American Society of Mechanical Engineers Fluid Dynamics Division, American Physical Society