A new scheme to determine the gravitational force perpendicular to the galactic plane as a function of the distance to the plane from stellar distances from the plane, velocity component perpendicular to the plane and ages has been applied to young runaway stars using narrow band photometry and Hipparcos astrometric data. This test of the method gives a run of the force in agreement with results of Bahcall. Hipparcos data have also been used to derive an improved velocity field for stars in the local stellar system called Gould's Belt. The galactic rotation parameters for young stars within this system differ drastically from those for stars outside. These differences are discussed in terms of an expansion and rotation of the Gould Belt.