You ride in a train, you have this helicopter toy. The train is not yet running when you flew your helicopter on a constant altitude (say 1 meter above the train's floor).
Question: What will happen on the flying helicopter toy when the train accelerates?
Will it stay relative to you and the train?
Will it move backward relative to you and the train and bump to the rear part of the train?
Will it move backward relative to you and the train for few seconds and then stay?
Any other thoughts?