How Everything Works
How Everything Works How Everything Works

Question 157

Since an object orbiting the earth is falling as it orbits, does it gradually get closer to the earth? Would it eventually reenter the earth's atmosphere and fall to the ground?-MG
If the orbiting object doesn't interact with anything but the earth, then the answer is: no, it will continue to orbit forever. That's because, although it is always falling and accelerating toward the earth, its sideways velocity continues to make it miss the earth. It just keeps on missing forever. Moreover, its total energy remains constant—the sum of its kinetic and gravitational potential energies. But if something removes some of its energy, it will gradually shift closer and closer to the earth and will reenter the atmosphere. That reentry occurs for low-lying satellites because they interact with the diffuse atoms in the extreme upper atmosphere. These satellites gradually lose energy and eventually come down in a blaze of frictionally heated material.

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