Mass in special relativity (including the kinetic energy of the gas) only when it is measured in the center of momentum frame. Just as is the case for single particles, the calculated "rest mass" of such a container of gas does not change when it is in motion, although its "relativistic mass" does change. The container may even be subjected to a force which gives it an overall velocity, or else (equivalently) it may be viewed from an inertial frame in which it has an overall velocity (that is, technically, a frame in which its center of mass has a velocity). In this case,
Tensor product of modules "R" of "N". Then the tensor product of "M" and "N" over "R" can be defined as the coequalizer: together with the requirements If "S" is a subring of a ring "R", then formula_1 is the quotient group of formula_155 by the subgroup generated by formula_156, where formula_157 is the image of formula_158 under formula_159 In particular, any tensor product of "R"-modules can be constructed, if so desired, as a quotient of a tensor product of abelian groups by imposing the "R"-balanced product property. In the construction of the tensor product over a commutative ring "R", the "R"-module structure can