The air in the compartment starts moving. So the situation is like being out in free air when a breeze starts to blow. If the fly had zero mass it would go exactly with it. Since it doesn't have zero mass, a "drag" effect will accelerate it and its speed will quickly approach the speed of the air. In the carriage it means that the fly will shift a little way to the back wall.
Hovering is flying in one spot without moving (much)
When you are driving, the objects inside the car are moving at the same speed and direction as the car, so they appear stationary relative to you. On the other hand, the objects outside the car are stationary or moving at varying speeds, which creates a visual contrast making them seem like they are moving relative to you.
Because there's no such thing as "really" stationary or "really" moving. If the distance between a point on one train and a point on the other train is changing, then a person on either train says that the other train is moving, and both of them are correct. A "stationary" train only appears to be moving if the train you're on is moving relative to that one.
The antonym of stationary is mobile.
stationary
The word for not moving is "stationary."
Here are some words that mean the opposite of stationary: active, mobile, moving, restless, unfixed, unsteady.
Stationary mean "not moving" so it must mean the the position is not moving or stay the same place.
One situation where you can be at rest and moving at the same time is when you are inside a moving vehicle. While you are stationary relative to the vehicle (at rest), you are moving relative to an observer outside the vehicle.
Stationary or immobile objects.
Any object that is not moving can be classed as stationary.
The opposite of moving would be not moving. The best opposite would be "stay put" or the similar concepts stay or remain. Another possible antonym is "stop" because it represents the opposite of something stationary that moves: something moving that becomes stationary.