how the earth rotates by itself?

Momentum imparted to it million of years ago when the solar system formed.

One theory involves glancing collision with a large asteroid millions of years ago that also broke off material that eventually developed into the moon.

I hope this helps a little more. Thanks for asking.

the moon causing colision altered the spin both in velocity and angle giving us our 23deg. tilt among other things. the Moon is as a brake on rotation. Since its formation the rotation of the earth has slowed from 8 to 24 horus per rotation

I just bought the newest book on the moon subject, "The Big Splat" by Dana Mackenzie ISBN 0-471-51057-6

sun's gravity pull

The rotation of the Earth is due to the initial momentum it received when the solar system formed. When the solar system was in its early stages, the matter that eventually formed the Earth was rotating. As gravity caused the matter to come together and form the Earth, the rotation continued and resulted in the spinning motion we observe today.

Another theory suggests that a glancing collision with a large asteroid millions of years ago played a role in the Earth's rotation. This collision not only contributed to the Earth's spin but also resulted in the formation of the Moon. The Moon's gravitational pull on the Earth has since affected its rotation by altering its velocity and angle. This interaction has resulted in the Earth's current tilt of approximately 23 degrees and has also acted as a brake, slowing down the Earth's rotation over time.

It is important to note that the Sun's gravity also plays a role in the Earth's rotation. The gravitational pull of the Sun affects the Earth, causing it to orbit around the Sun and also exerting a slight gravitational force that influences its rotation.

These explanations provide some insight into how the Earth rotates on its own axis, but they are based on scientific theories and research. Understanding the complex dynamics of planetary formation and celestial interactions requires continual scientific investigation and exploration.