In classical mechanics, linear momentum or translational momentum (pl. momenta; SI unit kg m/s, or, equivalently, N s) is the product of the mass and velocity of an object. For example, a heavy truck moving fast has a large momentum—it takes a large and prolonged force to get the truck up to this speed, and it takes a large and prolonged force to bring it to a stop afterwards. If the truck were lighter, or moving slower, then it would have less momentum.

Like velocity, linear momentum is a vector quantity, possessing a direction as well as a magnitude:

Linear momentum is also a conserved quantity, meaning that if a closed system is not affected by external forces, its total linear momentum cannot change. In classical mechanics, conservation of linear momentum is implied by Newton's laws; but it also holds in special relativity (with a modified formula) and, with appropriate definitions, a (generalized) linear momentum conservation law holds in electrodynamics, quantum mechanics, quantum field theory, and general relativity.

Read more about Momentum:  Newtonian Mechanics, Generalized Coordinates, Classical Electromagnetism, Quantum Mechanics, History of The Concept

Other articles related to "momentum":

Momentum - History of The Concept
... in Alexandria, Byzantine philosopher John Philoponus developed a concept of momentum in his commentary to Aristotle's Physics ... be read as a statement of the modern law of momentum, since he had no concept of mass as distinct from weight and size, and more importantly he believed that it is speed ... The first correct statement of the law of conservation of momentum was by English mathematician John Wallis in his 1670 work, Mechanica sive De Motu ...
Convection–diffusion Equation - Similar Equations in Other Contexts
... closely related to the Navier–Stokes equations, because the flow of momentum in a fluid is mathematically similar to the flow of mass or energy ... of an incompressible Newtonian fluid, in which case the Navier–Stokes equation is where M is the momentum of the fluid (per unit volume) at each point (equal to the density ... equation, the term on the left-hand side describes the change in momentum at a given point the first term on the right describes viscosity, which is really the diffusion of momentum ...
Momentum (finance)
... In finance, momentum is the empirically observed tendency for rising asset prices to rise further, and falling prices to keep falling ... The existence of momentum is a market anomaly, which finance theory struggles to explain ... have largely attributed the appearance of momentum to cognitive biases, which belong in the realm of behavioral economics ...
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Legal Momentum
... Legal Momentum, formerly known as NOW Legal Defense and Education Fund, is the oldest legal advocacy group for women in the United States ... Founded in 1970, Legal Momentum is a liberal multi-issue organization dedicated to advancing women’s rights across the country ... In its advocacy role, Legal Momentum maintains a public-access database of current and recent cases in litigation of interest to legal practitioners and people involved in or affected by gender ...