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In Newtonian mechanics, momentum (pl.: momenta or momentums; more specifically linear momentum or translational momentum) is the product of the mass and velocity of an object. It is a vector quantity, possessing a magnitude and a direction.
is the position vector (a vector from the point about which the torque is being measured to the point where the force is applied), and r is the magnitude of the position vector, F {\displaystyle \mathbf {F} } is the force vector, F is the magnitude of the force vector and F ⊥ is the amount of force directed perpendicularly to the position of ...
[19]: 14–15 The torque can vanish even when the force is non-zero, if the body is located at the reference point (=) or if the force and the displacement vector are directed along the same line. The angular momentum of a collection of point masses, and thus of an extended body, is found by adding the contributions from each of the points.
The moment of force, or torque, is a first moment: =, or, more generally, .; Similarly, angular momentum is the 1st moment of momentum: =.Momentum itself is not a moment.; The electric dipole moment is also a 1st moment: = for two opposite point charges or () for a distributed charge with charge density ().
However, it is a mathematical constraint, the natural consequence of the equations of motion, rather than a physical constraint (which would require extra constraint forces). Common examples include energy, linear momentum, angular momentum and the Laplace–Runge–Lenz vector (for inverse-square force laws).
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. Force plays an important role in classical mechanics.
Momentum is a vector quantity, so impulse is also a vector quantity: =. Newton’s second law of motion states that the rate of change of momentum of an object is equal to the resultant force F acting on the object: F = p 2 − p 1 Δ t , {\displaystyle \mathbf {F} ={\frac {\mathbf {p} _{2}-\mathbf {p} _{1}}{\Delta t}},}
In special relativity, four-momentum (also called momentum–energy or momenergy [1]) is the generalization of the classical three-dimensional momentum to four-dimensional spacetime. Momentum is a vector in three dimensions ; similarly four-momentum is a four-vector in spacetime .