Final answer:
Ellis feels like his head is still spinning after turning in circles due to the continued movement of the fluid in his ear's semicircular canals, which are part of the vestibular system responsible for balance and the detection of motion.
Step-by-step explanation:
The sensation of head spinning that Ellis feels after turning around in a circle is due to the activity of the fluid in the semicircular canals of his ears. These fluid-filled canals are a part of the vestibular system, which is responsible for maintaining balance and sensing angular acceleration and deceleration. When Ellis stops spinning, the fluid inside the semicircular canals continues to move, which causes the hair cells lining the canals to send nerve impulses that the brain interprets as continued spinning, resulting in a dizzy feeling.
This phenomenon is similar to the fictitious force called centrifugal force experienced when on a merry-go-round. The brain's processing of input from the three semicircular canals enables the detection of motion in three dimensions. However, even when Ellis stops spinning, the continued motion of the fluid in the canals leads to the sensation of dizziness until the fluid settles and the nerve impulses align with the actual lack of movement.