“Displace” is a verb meaning “to take over or force from its position or role”. Because the verb is transitive, it requires both a subject and an object: thing A (the subject) displaced thing B (the object). “Displaced” is not an adjective, but the past participle of the verb. Hence, when you say a thing has been displaced, it doesn't just mean “out of its typical environment”: it means “forced from its typical environment by something else”.
Some examples of “displaced” used correctly:
- When Archimedes sat down in his bathtub, he displaced a large amount of water and caused the tub to overflow. (The subject [Archimedes] took over the position of the object [water]).
- Digital cash registers have largely displaced mechanical ones in stores. (The subject [digital cash registers] took over the role of the object [mechanical cash registers]).
- Several visitors have asked about the displaced park bench. I told them it was hit by a reversing bus last week. (The object [park bench] has been forcibly moved from its normal location. The past participle is being used without a subject, i.e. in the passive voice).
The sentence “the displaced ball floats around” means something forced the ball from its normal position. While this may be literally true (the ball may have been forced by humans from a sports locker into a rocket, then forced by that rocket to the moon), the intended meaning is probably something more like “out of place” or “incongruous”.