Final answer:
The forces acting on a Ferris wheel in motion are gravitational force, normal force, and potentially frictional force, affecting the angular velocity and angular momentum of the wheel.
Step-by-step explanation:
When a Ferris wheel is loaded with people in chairs at the 4 o'clock, 1 o'clock, 9 o'clock, and 6 o'clock positions and begins to turn, the primary forces acting on the system are gravitational force, normal force, and frictional force (if considered). The gravitational force acts downwards, while the normal force acts perpendicular to the surface of the Ferris wheel. Once the wheel is in motion, the riders at varying positions around the wheel experience these forces differently, depending on their position relative to the ground. The gravitational force works along with centripetal force to keep the riders in circular motion. As the wheel turns, each person's weight creates a torque that must be balanced by the Ferris wheel's motor. This affects the angular velocity due to changes in rotational inertia when the riders are at different positions on the wheel. The angular momentum of the system is conserved unless an external torque acts on it.