What makes Earth to rotate on its axis?

Earth's rotation on its axis is a result of several key factors, both from its formation and ongoing physical principles.

Formation and Initial Angular Momentum

Earth's rotation originated from the formation of the Solar System about 4.6 billion years ago. A massive cloud of gas and dust, known as the solar nebula, began to collapse under its own gravity. As this cloud collapsed, it started to spin due to the conservation of angular momentum. This spinning motion increased as the material gathered more closely together, forming a disk shape. The planets, including Earth, inherited this spinning motion as they formed from this disk132.

Inertia and Continued Rotation

Once Earth formed and began spinning, it continued to do so due to inertia, which is the tendency of an object to resist changes in its state of motion. Since there are no significant forces strong enough to stop Earth's rotation, it persists to this day3.

External Influences

Although Earth's rotation is not halted, it is influenced by external forces, particularly tidal interactions with the Moon and, to a lesser extent, the Sun. These interactions have gradually slowed Earth's rotation over millions of years, increasing the length of a day from about 21 hours 600 million years ago to the current 24 hours2.

Recent Variations

In recent times, Earth's rotation has shown some variability. For instance, the melting of polar ice due to climate change has led to a slight increase in Earth's rotational speed, as the redistribution of mass towards the center of the Earth results in a faster spin according to the conservation of angular momentum2.

In summary, Earth's rotation is a legacy of the angular momentum it acquired during the formation of the Solar System, maintained by inertia, and slightly modified by ongoing external gravitational interactions.