Mass and energy are scalar quantities, while momentum is a vector quantity. This results in a coupled set of equations, called the Navier-Stokes equations, which describe how fluids behave when subjected to external forces.

Vector quantities - NASA

Mass and energy are scalar quantities, while momentum is a vector quantity. This results in a coupled set of equations, called the Navier-Stokes equations, which describe how fluids behave when subjected to external forces.

Vector quantities - NASA

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