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In physics, action is a scalar quantity that describes how the balance of kinetic versus potential energy of a physical system changes with trajectory. Action is significant because it is an input to the principle of stationary action, an approach to classical mechanics that is simpler for multiple objects. [1]
Every object in a 2-body ballistic trajectory has a constant specific orbital energy equal to the sum of its specific kinetic and specific potential energy: = = =, where = is the standard gravitational parameter of the massive body with mass , and is the radial distance from its center. As an object in an escape trajectory moves outward, its ...
Action principles are "integral" approaches rather than the "differential" approach of Newtonian mechanics.[2]: 162 The core ideas are based on energy, paths, an energy function called the Lagrangian along paths, and selection of a path according to the "action", a continuous sum or integral of the Lagrangian along the path.
Mechanics (from Ancient Greek μηχανική (mēkhanikḗ) 'of machines') [1] [2] is the area of physics concerned with the relationships between force, matter, and motion among physical objects. [3] Forces applied to objects may result in displacements, which are changes of an object's position relative to its environment.
The study of mechanics is complicated by the fact that household words like energy are used with a technical meaning. [10] [11] Moreover, words which are synonymous in everyday speech are not so in physics: force is not the same as power or pressure, for example, and mass has a different meaning than weight.
The energy that a physical body possesses due to its motion, defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. The body continues to maintain this kinetic energy unless its velocity changes. Contrast potential energy. Kirchhoff's circuit laws. Also called Kirchhoff's rules or simply Kirchhoff's laws.
In quantum mechanics, energy is defined in terms of the energy operator (Hamiltonian) as a time derivative of the wave function. The Schrödinger equation equates the energy operator to the full energy of a particle or a system. Its results can be considered as a definition of measurement of energy in quantum mechanics.
Nuclear energy is energy stored in interactions between the particles in the atomic nucleus and is studied in nuclear physics. [25] Electromagnetic energy is in the form of electric charges, magnetic fields, and photons. It is studied in electromagnetism. [26] [27] Various forms of energy in quantum mechanics; e.g., the energy levels of ...