Why does the Earth rotate?

The Earth rotates because of the conservation of angular momentum acquired from the rotation of the solar nebula, a gaseous cloud that is believed to have formed the solar system.

Angular momentum is the measure of a rotating object’s tendency to continue spinning. It stays constant until external forces stop the object’s rotation.

The nebula that predated the solar system collapsed because of its own gravity about 4.6 billion years ago. It began to spin as it collapsed, resulting in eddies of dust and gas that stuck together and condensed to form the Sun and the planets. These bodies, including Earth, inherited the angular momentum of the nebula. The conservation of that angular momentum and the absence of significant external torques acting on Earth contribute to its continued rotation.