In a lattice, the product of h-bar with the wave vector of the lattice gives the crystal variety of this property, which is sometimes assigned to phonons. In 2010 Barnett resolved a century long controversy by showing that both Abraham and Minkowski had correct formulae for this quantity for light in a medium. One form of this quantity is only conserved for central forces while Planck's constant is divided by another to get the de Broglie wavelen
In a lattice, the product of h-bar with the wave vector of the lattice gives the crystal variety of this property, which is sometimes assigned to phonons. In 2010 Barnett resolved a century long controversy by showing that both Abraham and Minkowski had correct formulae for this quantity for light in a medium. One form of this quantity is only conserved for central forces while Planck's constant is divided by another to get the de Broglie wavelength. Relativistically this is described as a 4-vector with the relativistic energy over c being the first term. This quantity is conserved in both elastic an inelastic collisions. Appearing in the original form of Newton's Second law, the linear version of this quantity , when crossed with the position vector, gives the Angular form of this quantity. FTP, name this quantity which is always conserved and which is typically given for linear motion as mass times velocity.
In a lattice, the product of h-bar with the wave vector of the lattice gives the crystal variety of this property, which is sometimes assigned to phonons.
momentum [Anti prompt on linear or angular momentum before those words are mentioned]  