86.3 Kepler's laws of planetary motion 3. Kepler’ s third law If fis the time that it takes for a planet to make one full revolution around the sun and if a is half major axis of the ellipse then P252~P254 2、4z2 GM M 86.4 The gravitational field and Gausss law for the the gravitational field 1. The gravitational field The existence of M sets up or establishes the gravitational field at all points in space whether the other mass m is presented or not. g(7) F Gm r The gravitational field can be imagined as the force per unit mass at a given point in space. It is the same as the acceleration due to gravity at that location14 §6.3 Kepler’s laws of planetary motion 3. Kepler’s third law If T is the time that it takes for a planet to make one full revolution around the sun, and if a is half major axis of the ellipse, then 3 2 2 4 a GM T π = M a P252~P254 m §6.4 The gravitational field and Gauss’s law for the the gravitational field 1. The gravitational field The existence of M sets up or establishes the gravitational field at all points in space whether the other mass m is presented or not. r r GM m F g(r) ˆ 2 = = − r r The gravitational field can be imagined as the force per unit mass at a given point in space. It is the same as the acceleration due to gravity at that location