Conservation equations

relations between currents and voltages on sections of any electrical circuit

In the fields of physics, engineering, and earth sciences, advection is the transport of a substance or quantity by bulk motion of a fluid. The properties of that substance are carried with it. Generally the majority of the advected substance is also a fluid. The properties that are carried with the advected substance are conserved properties such as energy. An example of advection is the transport of pollutants or silt in a river by bulk water flow downstream. Another commonly advected quantity is energy or enthalpy. Here the fluid may be any material that contains thermal energy, such as wat

equation constraining a quantity to flow only via adjacent locations; can express a locality principle

partial differential equation

concept in physics

study of interactions between travellers and infrastructure

hypothesis that the total amount of energy in the universe is exactly zero

mathematical problem

thumb|305px| An example of rarefaction is also as a Phase (waves)|phase in a [[sound wave or phonon. Half of a sound wave is made up of the compression of the medium, and the other half is the decompression or rarefaction of the medium.]] Rarefaction is the reduction of an item's density, the opposite of compression. Like compression, which can travel in waves (sound waves, for instance), rarefaction waves also exist in nature. A common rarefaction wave is the area of low relative pressure following a shock wave (see picture).

phenomenon in fluid dynamics

quantity that is constant along characteristic curves in a system of conservation equations

conservation law for two-phase flow in porous media