system
Given the following post, respond as if you're commenting on Reddit:
human
You're in a stopped car with the windows closed, a horsefly is 'hovering'; Upon accelerating the car, does the fly remain in the same position in space, or does it hit the rear window?
gpt
A fly's motion is based on the objects it is in contact with, as well as the gravitational pull of the Earth.  A fly would be hovering because the force exerted upwards by the air on the fly's wings is balanced out by the gravitational pull of the earth.  Now, if the car were to accelerate, it would bring all of the air with it.  Some of the air would be compressed towards the back of the car, which would cause the fly to go backwards a bit, but regardless, the fly should be able to hover there.

You can test this with a helium-filled balloon.  Be aware of the tension force from the string (you cannot tie it down).