![<span class="mw-page-title-main">Angular momentum</span> Conserved physical quantity; rotational analogue of linear momentum](https://upload.wikimedia.org/wikipedia/commons/b/b9/Gyroskop.jpg)
Angular momentum is the rotational analog of linear momentum. It is an important physical quantity because it is a conserved quantity – the total angular momentum of a closed system remains constant. Angular momentum has both a direction and a magnitude, and both are conserved. Bicycles and motorcycles, flying discs, rifled bullets, and gyroscopes owe their useful properties to conservation of angular momentum. Conservation of angular momentum is also why hurricanes form spirals and neutron stars have high rotational rates. In general, conservation limits the possible motion of a system, but it does not uniquely determine it.
Continuum mechanics is a branch of mechanics that deals with the deformation of and transmission of forces through materials modeled as a continuous medium rather than as discrete particles. The French mathematician Augustin-Louis Cauchy was the first to formulate such models in the 19th century.
![<span class="mw-page-title-main">Force</span> Influence that can change motion of an object](https://upload.wikimedia.org/wikipedia/commons/thumb/c/c3/Force_examples.svg/320px-Force_examples.svg.png)
A force is an influence that can cause an object to change its velocity unless counterbalanced by other forces. The concept of force makes the everyday notion of pushing or pulling mathematically precise. Because the magnitude and direction of a force are both important, force is a vector quantity. The SI unit of force is the newton (N), and force is often represented by the symbol F.
![<span class="mw-page-title-main">Fluid dynamics</span> Aspects of fluid mechanics involving flow](https://upload.wikimedia.org/wikipedia/commons/thumb/a/a5/Teardrop_shape.svg/320px-Teardrop_shape.svg.png)
In physics, physical chemistry and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids — liquids and gases. It has several subdisciplines, including aerodynamics and hydrodynamics. Fluid dynamics has a wide range of applications, including calculating forces and moments on aircraft, determining the mass flow rate of petroleum through pipelines, predicting weather patterns, understanding nebulae in interstellar space and modelling fission weapon detonation.
![<span class="mw-page-title-main">Kinetic energy</span> Energy of a moving physical body](https://upload.wikimedia.org/wikipedia/commons/thumb/3/30/Wooden_roller_coaster_txgi.jpg/320px-Wooden_roller_coaster_txgi.jpg)
In physics, the kinetic energy of an object is the form of energy that it possesses due to its motion.
![<span class="mw-page-title-main">Momentum</span> Property of a mass in motion](https://upload.wikimedia.org/wikipedia/commons/thumb/8/86/Billard.JPG/320px-Billard.JPG)
In Newtonian mechanics, momentum is the product of the mass and velocity of an object. It is a vector quantity, possessing a magnitude and a direction. If m is an object's mass and v is its velocity, then the object's momentum p is:
![<span class="mw-page-title-main">Equations of motion</span> Equations that describe the behavior of a physical system](https://upload.wikimedia.org/wikipedia/commons/thumb/6/68/Velocity_vs_time_graph_for_average_acceleration_that_shows_dependence_on_time.jpg/320px-Velocity_vs_time_graph_for_average_acceleration_that_shows_dependence_on_time.jpg)
In physics, equations of motion are equations that describe the behavior of a physical system in terms of its motion as a function of time. More specifically, the equations of motion describe the behavior of a physical system as a set of mathematical functions in terms of dynamic variables. These variables are usually spatial coordinates and time, but may include momentum components. The most general choice are generalized coordinates which can be any convenient variables characteristic of the physical system. The functions are defined in a Euclidean space in classical mechanics, but are replaced by curved spaces in relativity. If the dynamics of a system is known, the equations are the solutions for the differential equations describing the motion of the dynamics.
![<span class="mw-page-title-main">Gravitational field</span> Model in physics](https://upload.wikimedia.org/wikipedia/commons/thumb/4/4f/Earth-moon-field.svg/320px-Earth-moon-field.svg.png)
In physics, a gravitational field or gravitational acceleration field is a vector field used to explain the influences that a body extends into the space around itself. A gravitational field is used to explain gravitational phenomena, such as the gravitational force field exerted on another massive body. It has dimension of acceleration (L/T2) and it is measured in units of newtons per kilogram (N/kg) or, equivalently, in meters per second squared (m/s2).
In theoretical physics and mathematical physics, analytical mechanics, or theoretical mechanics is a collection of closely related formulations of classical mechanics. Analytical mechanics uses scalar properties of motion representing the system as a whole—usually its kinetic energy and potential energy. The equations of motion are derived from the scalar quantity by some underlying principle about the scalar's variation.
![<span class="mw-page-title-main">Rigid body dynamics</span> Study of the effects of forces on undeformable bodies](https://upload.wikimedia.org/wikipedia/commons/thumb/f/f2/SteamEngine_Boulton%26Watt_1784.png/320px-SteamEngine_Boulton%26Watt_1784.png)
In the physical science of dynamics, rigid-body dynamics studies the movement of systems of interconnected bodies under the action of external forces. The assumption that the bodies are rigid simplifies analysis, by reducing the parameters that describe the configuration of the system to the translation and rotation of reference frames attached to each body. This excludes bodies that display fluid, highly elastic, and plastic behavior.
In classical mechanics, the Laplace–Runge–Lenz (LRL) vector is a vector used chiefly to describe the shape and orientation of the orbit of one astronomical body around another, such as a binary star or a planet revolving around a star. For two bodies interacting by Newtonian gravity, the LRL vector is a constant of motion, meaning that it is the same no matter where it is calculated on the orbit; equivalently, the LRL vector is said to be conserved. More generally, the LRL vector is conserved in all problems in which two bodies interact by a central force that varies as the inverse square of the distance between them; such problems are called Kepler problems.
A classical field theory is a physical theory that predicts how one or more fields in physics interact with matter through field equations, without considering effects of quantization; theories that incorporate quantum mechanics are called quantum field theories. In most contexts, 'classical field theory' is specifically intended to describe electromagnetism and gravitation, two of the fundamental forces of nature.
In physics, relativistic mechanics refers to mechanics compatible with special relativity (SR) and general relativity (GR). It provides a non-quantum mechanical description of a system of particles, or of a fluid, in cases where the velocities of moving objects are comparable to the speed of light c. As a result, classical mechanics is extended correctly to particles traveling at high velocities and energies, and provides a consistent inclusion of electromagnetism with the mechanics of particles. This was not possible in Galilean relativity, where it would be permitted for particles and light to travel at any speed, including faster than light. The foundations of relativistic mechanics are the postulates of special relativity and general relativity. The unification of SR with quantum mechanics is relativistic quantum mechanics, while attempts for that of GR is quantum gravity, an unsolved problem in physics.
![<span class="mw-page-title-main">Stokes flow</span> Type of fluid flow](https://upload.wikimedia.org/wikipedia/commons/thumb/a/ae/Stokes_sphere.svg/320px-Stokes_sphere.svg.png)
Stokes flow, also named creeping flow or creeping motion, is a type of fluid flow where advective inertial forces are small compared with viscous forces. The Reynolds number is low, i.e. . This is a typical situation in flows where the fluid velocities are very slow, the viscosities are very large, or the length-scales of the flow are very small. Creeping flow was first studied to understand lubrication. In nature, this type of flow occurs in the swimming of microorganisms and sperm. In technology, it occurs in paint, MEMS devices, and in the flow of viscous polymers generally.
Fluid mechanics is the branch of physics concerned with the mechanics of fluids and the forces on them. It has applications in a wide range of disciplines, including mechanical, aerospace, civil, chemical, and biomedical engineering, as well as geophysics, oceanography, meteorology, astrophysics, and biology.
![<span class="mw-page-title-main">Classical mechanics</span> Description of large objects physics](https://upload.wikimedia.org/wikipedia/commons/4/4e/Orbital_motion.gif)
Classical mechanics is a physical theory describing the motion of objects such as projectiles, parts of machinery, spacecraft, planets, stars, and galaxies. The development of classical mechanics involved substantial change in the methods and philosophy of physics. The qualifier classical distinguishes this type of mechanics from physics developed after the revolutions in physics of the early 20th century, all of which revealed limitations in classical mechanics.
![<span class="mw-page-title-main">Lagrangian mechanics</span> Formulation of classical mechanics](https://upload.wikimedia.org/wikipedia/commons/1/19/Lagrange_portrait.jpg)
In physics, Lagrangian mechanics is a formulation of classical mechanics founded on the stationary-action principle. It was introduced by the Italian-French mathematician and astronomer Joseph-Louis Lagrange in his presentation to the Turin Academy of Science in 1760 culminating in his 1788 grand opus, Mécanique analytique.
In physics, the n-body problem is the problem of predicting the individual motions of a group of celestial objects interacting with each other gravitationally. Solving this problem has been motivated by the desire to understand the motions of the Sun, Moon, planets, and visible stars. In the 20th century, understanding the dynamics of globular cluster star systems became an important n-body problem. The n-body problem in general relativity is considerably more difficult to solve due to additional factors like time and space distortions.
![<span class="mw-page-title-main">Gravitoelectromagnetism</span> Analogies between Maxwells and Einsteins field equations](https://upload.wikimedia.org/wikipedia/commons/thumb/7/7a/Gravity_Probe_B_Confirms_the_Existence_of_Gravitomagnetism-en.jpg/320px-Gravity_Probe_B_Confirms_the_Existence_of_Gravitomagnetism-en.jpg)
Gravitoelectromagnetism, abbreviated GEM, refers to a set of formal analogies between the equations for electromagnetism and relativistic gravitation; specifically: between Maxwell's field equations and an approximation, valid under certain conditions, to the Einstein field equations for general relativity. Gravitomagnetism is a widely used term referring specifically to the kinetic effects of gravity, in analogy to the magnetic effects of moving electric charge. The most common version of GEM is valid only far from isolated sources, and for slowly moving test particles.