We know earth is spinning that's why we have day night cycle .. but why it's spinning ?
Answer:-
If earth wasn't spinning then it doesn't have life. But every planet have spin .. because torque due to moon and sun .. now earth have some mass so earth-sun system due to two body central force problem it should not rotate about the sun center but near to sun center .this result a external torque on sun and also done by others planet in same direction so it has an resultant up or down spin.. similarly moon-earth system the moon doesn't rotate around the centre of earth but near to center of earth and sun gravity .this result a continuous external torque and earth is spinning..