throw, hurl, throw away, cast
扔 centers on forceful, decisive hand action: throwing, hurling, or casting something away. The idea of discarding or throwing away is a natural extension of that same forceful motion.
扔 combines the hand radical 扌 with 乃, which likely contributes a phonetic element. The exact historical development is uncertain, but the structure suggests a hand action related to throwing or discarding.
The hand radical 扌 beside 乃 looks like a hand winding up to throw something. Picture a hand gripping an object and hurling it away with force.
For ジョウ, imagine a strongman named Joe hurling a heavy object: Joe -> ジョウ, and his powerful throw sends it flying.