ASTR 101 Lecture Notes - Lecture 5: Inverse-Square Law, Escape Velocity, Hyperbola
10 Feb 2017
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The force of gravitational attraction between two bodies is proportional to their masses and inversely proportional to the square of the distance between them. Consider a spherically symmetric body one that looks the same no matter what direction you drill into it (stars, planets, etc. ) The attraction of the whole sphere is as if all its mass were concentrated at its center. If an unbalanced force acts on an object. For every force, this is always an equal and opposite reaction force. Newton realized the same force that causes the apple to fall keeps the moon orbiting the earth. The moon is constantly falling to earth but its sideways motion keeps it from crashing into earth. Orbiting objects are in freefall: e. g. For every 1km sideways, the moon falls about 1mm towards eartg, keeping it in an almost circular orbit around earth.
