model ClassicGravitation
  "Newtonian"
  parameter Real    G=6.674e-11             "Gravitational Constant";
  Real              m_1(unit="kilogram")    "mass #1";
  Real              m_2(unit="kilogram")    "mass #2";
  Real              r(unit="meter")         "radius";
  Real              F                       "force";
equation
  F = (G * m_1 * m_2) / (r^2);
end ClassicGravitation;