Tampan, Paminggir people. Lampung region of Sumatra, near Semangka Bay, 19th century, 64 x 64 cm. Photograph by D Dunlop. From the library of Darwin Sjamsudin, Jakarta. |

Let P be a material particle in a stable balance with its environment. It might be emitting and absorbing lots of photons, but not melting or breaking into pieces. More exactly, let P be in dynamic equilibrium with its surroundings. Then it is presumably steady enough so that we can model P using a sequence of excited states. Let these states be described by their density $\varrho$. And recall that the constant number $k_{\sf{F}}$ was introduced earlier to grasp the shape of a particle. Then we say that P is a **Newtonian** particle if it is so dense that

$k_{\sf{F}} \ll \varrho$

This quality implies that Newtonian particles are heavy, as shown below. And later we show how interactions between Newtonian particles obey conservation laws for mass and mechanical energy.

$m c^{2} \simeq \left| \, H \, \right|$

$W^{2} \ll H ^{2}$