An air conditioner at rest will remain at rest unless it is acted upon by a careless dolt (me) who doesn’t hold onto it during removal. An air conditioner in motion will remain in motion until it is acted upon by the mass of the planet earth beneath my backyard patio.
This little accident could have been a lot worse if I hadn’t unplugged the a/c unit or if it struck my patio table, a window, an animal or a person. As it happened, it was just an embarrassing way to unnecessarily dispose of a cheap, 9-year-old air conditioner.
To prevent your own unplanned physics experiment, use two people to install and remove even small air conditioners, and build or buy triangular braces to support the weight of the air conditioner when the window sash is open.