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• The force of gravity rules the universe.
• It governs our everyday lives on Earth and it controls the motions of the heavens above.
• Yet it is one of the least understood of all the forces of nature.
• To endeavor to understand this fundamental force is to experience anew something as simple as getting out of bed, throwing a ball, or diving into a pool; and it gives deep insight into the central organizing principle of the cosmos.
• Consider these crucial aspects of gravity: Gravity governs the rising and falling of tides—not only tides in the ocean, but tides in the solid rock of Earth itself.