  If we assume that the source of thermodynamic system, $\rho$ and $p$, are
also the source of gravity, thermal quantities, such as entropy, temperature,
and chemical potential, can induce effects of gravity, or gravity can induce
thermal effects. We find only for systems with constant temperature and zero
chemical potential, gravity can be seen as an entropic force. The case for
Newtonian approximation is discussed.
