Conceptual Physics (12th Edition)

Published by Addison-Wesley

Chapter 9 - Think and Discuss: 93

Answer

If Earth and the moon had the same mass, indeed they would rotate around a common point exactly halfway between them. However, the Earth is so much more massive than the moon (by a factor of about 80) that the Earth and Moon rotate about a point, known as the barycenter of the Earth-moon system, that lies within the Earth. The barycenter is about 4700 km (about 3/4 of an Earth radius) from the Earth’s center.

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