It takes power to rotate in a gravitational field, because there are tides that pull both Earth & Moon into little ovoids and cause friction. After a long enoug

It takes power to rotate in a gravitational field, because there are tides that pull both Earth & Moon into little ovoids and cause friction. After a long enough time any pair of orbiting bodies will become tidally locked. This is especially true when objects are relatively close compared to their diameter (moon is only 30 earths away), and the smaller object will lock much sooner, because it has much less angular momentum.