Base unit (measurement) aspects of the world, such as time, distance, velocity, mass, temperature, energy, and weight, and "units" are used to describe their magnitude or quantity. Many of these quantities are related to each other by various physical laws, and as a result the units of a quantities can be generally be expressed as a product of powers of other units; for example, momentum is mass multiplied by velocity, while velocity is measured in distance divided by time. These relationships are discussed in dimensional analysis. Those that can be expressed in this fashion in terms of the base units are called .
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