  A methodology is proposed for formulating dynamic equations in
thermo-piezoelectric and dissipative media from the first principle of energy
conservation. The results are in agreement with those from Hamiltonian
principle. Our formulations based on energy conservation are much easier to
understand. What is more is that, the energy conservation based framework is
able to handle dissipation problems, which is usually behind the scope of
Hamiltonian principle. In our case, the mechanical, electric and thermal
phenomena firstly are taken into account, and then the medium with dissipation
is included. The formulations on acoustic dynamic equation and the associated
constitutive relations of the medium will also pave an alternative way in
computational dynamic modelling based on weak formulations. In addition, our
methodology may be extended to other dynamic equation formulations, such as in
electrodynamics, fluid mechanics and quantum mechanics. This is especially true
for tackling the problems with multi-physical field interactions and coupling.
