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Physics Help » Physics Tutorial Index » Physics Tutorial: Gravity and Satellites
Gravity, a force that pulls masses together, is described by Newton’s Law of Universal Gravitation:
two bodies attract each other with a gravitational force which is proportional to the mass of each body and inversely proportional to the square of the distance between their centers.
Satellites orbiting the earth have velocity. They are held in an orbit by the force of gravity between the earth and the satellites. This is similar to an apple falling from a tree. When an apple falls it hits the ground. A satellite is constantly falling toward the ground, it just never reaches the ground like an apple would. This is because the earth curves out from under the satellite so it never reaches the earth’s surface.
Gravity's ARC: The Story of Gravity from Aristotle to Einstein and Beyond  In Gravity's Arc, you'll discover how some of the most colorful, eccentric, and brilliant people in history first locked, then unlocked the door to understanding one of nature's most essential forces. You'll find out why Aristotle's misguided conclusions about gravity became an unassailable part of Christian dogma, how Galileo slowed down time to determine how fast objects fall, and why Isaac Newton erased every mention of one man's name from his magnum opus Principia. You'll also figure out what Einstein meant when he insisted that space is curved, whether there is really such a thing as antigravity, and why some scientists think that the best way to get to outer space is by taking an elevator. Gravity's ARC: The Story of Gravity from Aristotle to Einstein and Beyond
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