For angular acceleration. This type of acceleration occurs when a spherical object rotates. Again, when an object is rotated in a circular motion, the same angular acceleration is created in that object. For example, if an object is tied in a thread and rotated around in a circular path, you will see that it automatically revolves in a circular path. The same thing happens in the case of the earth. Since the earth is round and its orbit around the sun is also round, the acceleration caused by its motion when the earth rotates is angular acceleration. Again, its center-facing force towards the sun and its outward force towards the outside are equal. So even if it wants to move forward for the acceleration created at the front, it moves backwards towards the center for center-facing attraction. In this way, the earth revolves in a circular way again and again for the angular acceleration created at every moment.