Mechanical Energy
 Paul Dirac in 1933.

Consider a particle P that is described by its rest mass $m$ and momentum $p$. And please notice that these numbers have been defined by a methodical description of sensation. Definition: the mechanical energy of P is

$E \equiv \sqrt{ c^{2}p^{2} + m^{2}c^{4} \vphantom{\sum^{2}} \; }$

where $c$ is a constant. This statement comes from . And here are some special cases.

$E \simeq \gamma m c^{2}$

$E \left( {\large{\gamma}} \right) =2 \, \left| \, H_{chem}^{\mathcal{A}} \vphantom{{H_{chem}^{\large{\gamma}}}^{9}} \right|$

 Next step: measuring mechanical energy.