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Momentum

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This article is about momentum in physics. For other uses, see Momentum (disambiguation).

In a game of pool, momentum is conserved; that is, if one ball stops dead after the collision, the other ball will continue away with all the momentum. If the moving ball continues or is deflected then both balls will carry a portion of the momentum from the collision,
Common symbol(s):	p
SI unit:	kg m/s or N s

Classical mechanics
History of classical mechanics Timeline of classical mechanics
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Fundamental concepts[hide] Space Time Mass Inertia Velocity Speed Acceleration Force Momentum Impulse Torque / Moment / Couple Angular momentum Moment of inertia Reference frame Energy Kinetic energy Potential energy Mechanical work Mechanical power Virtual work D'Alembert's principle
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v t e

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.

Contents 1 Newtonian mechanics 1.1 Single particle 1.2 Many particles 1.3 Relation to force 1.4 Conservation 1.5 Dependence on reference frame 1.6 Application to collisions 1.7 Multiple dimensions 1.8 Objects of variable mass 2 Generalized coordinates 2.1 Lagrangian mechanics 2.2 Hamiltonian mechanics 2.3 Symmetry and conservation 3 Relativistic mechanics 3.1 Lorentz invariance 3.2 Four-vector formulation 4 Classical electromagnetism 4.1 Vacuum 4.2 Media 4.3 Particle in field 5 Quantum mechanics 6 Deformable bodies and fluids 6.1 Conservation 6.2 Acoustic waves 7 History of the concept 8 See also 9 Notes 10 References 11 Further reading 12 External links

Newtonian mechanics

Momentum has a direction as well as magnitude. Quantities that have both a magnitude and a direction are known as vector quantities. Because momentum has a direction, it can be used to predict the resulting direction of objects after they collide, as well as their speeds. Below, the basic properties of momentum are described in one dimension. The vector equations are almost identical to the scalar equations (see multiple dimensions).