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
Escape velocity "r" from the center of mass of the planet, whose mass is "M". Its initial speed is equal to its escape velocity, formula_6. At its final state, "f", it will be an infinite distance away from the planet, and its speed will be negligibly small and assumed to be 0. Kinetic energy "K" and gravitational potential energy "U" are the only types of energy that we will deal with, so by the conservation of energy, "K" = 0 because final velocity is zero, and "U" = 0 because its final distance is infinity, so where μ is the standard gravitational