Eloise is holding a helium-filled balloon on a string while standing in a train that is moving at a steady speed. She is facing forward in the direction the train is moving. If the train suddenly comes to a quick stop, what happens to the balloon and why, from Eloise's perspective?
Respond briefly.
When the train comes to a quick stop, Eloise and any loose objects in the train will experience an inertia effect, causing them to continue moving forward due to their momentum. The helium-filled balloon, however, will move in the opposite direction - it will shift backward toward the rear of the train. This occurs because the balloon is buoyant and less dense compared to the air inside the train. The air, being more inertial, moves forward when the train stops. As a result, it creates a temporary high-pressure area at the front of the train and a low-pressure area at the back. The balloon moves from the high-pressure area toward the low-pressure area, which is toward the back of the train, opposite to the direction of Eloise's forward momentum. From Eloise's perspective, while she feels the force pushing her forward as the train stops, she will observe the balloon moving backward, away from her and toward the rear of the train.