home | alphabetical index | |||||||

## Momentum
In physics,
## Momentum in classical mechanics
In classical mechanics, momentum (traditionally written as The SI unit of momentum is newton-seconds, which can alternatively be expressed with the units kg.m/s. An impulse changes the momentum of an object. An impulse is calculated as the integral of force with respect to duration. ## Momentum in relativistic mechanics
It is commonly believed that the physical laws should be invariant under translationss. Thus, the definition of momentum was changed when Einstein formulated Special relativity so that its magnitude would remain invariant under relativistic transformations. See physical conservation law. We now define a vector, called the
- [
*E/c*]**p**
E is the total energy of the system, and is called the "relativistic momentum" defined thus:p
*E*= γ*mc*^{2}
= γ**p***m***v**
- .
The "length" of the vector that remains constant is defined thus:
=pE/c, where E is the energy the photon carries and c is the speed of light.## Momentum in quantum mechanicsIn quantum mechanics momentum is defined as an operator on the wave function. The Heisenberg uncertainty principle defines limits on how accurately the momentum and position of a single observable system can be known at once. ## Figurative use | |||||||

copyright © 2004 FactsAbout.com |