  A classical model of a stable particle of finite size is studied. The model
parameters can be chosen such that the described particle has the mass and
radius of a proton. Using the energy-momentum tensor (EMT), we show how the
presence of long-range forces alters some notions taken for granted in
short-range systems. We focus our attention on the D-term form factor. The
important conclusion is that a more careful definition of the D-term may be
required when long-range forces are present.
