A student stands on a moving sidewalk inside an airport terminal and tosses a small rubber ball straight upward relative to her own position. Three observers watch the event under the following conditions.
• Observer G is at rest on the ground outside the terminal.
• Observer S is the student herself, who moves with the sidewalk at a constant speed of 2.0 m/s relative to the ground.
• Observer A rides another sidewalk section that begins from rest but is speeding up at a steady 0.50 m/s² along the same straight line as the first sidewalk.
All sidewalks are level and friction between the ball and air is negligible. The ball is tossed and caught at the same height relative to the student.
Assume that the gravitational field is uniform and constant during the brief flight of the ball.
(a) For each observer (G, S, and A), describe the horizontal path of the ball that the observer actually sees during the toss–catch sequence. State whether it appears to move in a straight line or along a curved trajectory.
(b) Identify which of the three observers’ reference frames can be classified as inertial, and which cannot. Provide clear justification based on the motion you described in part (a).
(c) One of the observers claims that Newton’s first law is violated because the ball appears to curve even though no horizontal force seems to act on it. Explain how your answers above resolve this apparent contradiction.