A balance equation expresses the change of physical quantities with respect to time. For three-dimensional bodies, the physical quantity can flow through the surface of the balance volume and be generated or vanish inside the volume. Balancing the conserved quantities’ mass, momentum, and moment of momentum yields the fundamental equations of mechanics. Balancing the conserved quantity energy and the non-conserved entropy yields the laws of thermodynamics.
balance of mass
balance of momentum
balance of moment of momentum
balance of energy
balance of entropy.
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