How Everything Works
How Everything Works How Everything Works

Question 717

What source of energy keeps the earth and the planets orbiting the sun or keeps electrons orbiting the nuclei of atoms? - AW
It takes no additional energy to keep those objects orbiting—the earth's inertia keeps it moving around the sun. If the sun weren't there, the earth would continue forward in a straight line at a steady pace forever because that is how free objects behave. It takes no energy or force to keep them moving. But the earth is drawn continuously inward by the sun's gravity and so it travels in an elliptical arc instead of a straight line. Assuming that nothing adds or subtracts energy from the earth and sun, the earth will continue to orbit the sun forever. The same applies for the other planets and for electrons orbiting nuclei in an atom. In the latter case, it is electromagnetic forces that draw the electrons inward, rather than gravity.

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