Derivation of the Navier–Stokes equations equation), three important concepts may be concisely written: conservation of mass, conservation of momentum, and conservation of energy. Validity is retained if formula_5 is a vector, in which case the vector-vector product in the second term will be a dyad. A general momentum equation is obtained when the conservation relation is applied to momentum. If the intensive property formula_5; considered is the mass flux (also "momentum density"), i.e. the product of mass density and flow velocity formula_17, by substitution in the general continuum equation: where formula_19 is a dyad, a special case of tensor product, which results in a second
Brain-to-body mass ratio animals usually have larger brains than smaller animals); the relationship is not, however, linear. Small mammals such as mice may have a brain/body ratio similar to humans, while elephants have a comparatively lower brain/body ratio. In animals, it is thought that the larger the brain, the more brain weight will be available for more complex cognitive tasks. However, large animals need more neurons to represent their own bodies and control specific muscles; thus, relative rather than absolute brain size makes for a ranking of animals that better coincides with the observed complexity of animal behaviour. The relationship between brain-to-body mass