In classical field theory, translational (in space and time) symmetry leads the derivation of the energy-momentum tensor using Noether's theorem. From this it is possible to derive four conserved charges. The first turns out to be the Hamiltonian, and thus we have energy conservation. The remaining three turn out to be Pi=-∫d3xπa∂iφa where φa are fields and πa are their conjugate momentum densities. It is often stated that these are the three (physical) momentum components, and so we have conservation of momentum. Is there an easy way to see that this is true?