13CHAPTER OUTLINE13.1 Newton’s Law of UniversalGravitation13.2Measuring the GravitationalConstant13.3Free-Fall Acceleration andthe Gravitational Force13.4Kepler’s Laws and theMotion of Planets13.5The Gravitational Field13.6Gravitational PotentialEnergy 13.7Energy Considerations inMotionPlanetary and SatelliteUniversal GravitationANSWERS TO QUESTIONSQ13.1Because gis the same for all objects near the Earth’s surface.The larger mass needs a larger force to give it just the sameacceleration.Q13.2To a good first approximation, your bathroom scale reading isunaffected because you, the Earth, and the scale are all in freefall in the Sun’s gravitational field, in orbit around the Sun. Toa precise second approximation, you weigh slightly less atnoon and at midnight than you do at sunrise or sunset. TheSun’s gravitational field is a little weaker at the center of theEarth than at the surface subsolar point, and a little weaker stillon the far side of the planet. When the Sun is high in your sky,
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