Gravity and Motion 79
2.1 Solving the Problem of Astronomical Motion 80
2.2 Inertia 80
2.3 Orbital Motion and Gravity 82
2.4 Newton's Second Law of Motion 83
Acceleration 83
Mass 84
2.5 The Law of Gravity 85
2.6 Newton's Third Law of Motion 85
2.7 Measuring a Body's Mass Using Orbital Motion 86
2.8 Surface Gravity 88
2.9 Escape Velocity 90