Gravity traps are often used by kingdoms to prevent airborne enemies. As sixth-grade people could freely move in the air, some kingdoms created a lot of countermeasures against airborne enemies.
The trap will suddenly increase the gravity above them and pull everything in the air. This is a nasty trap for airborne enemies since the sudden gravity increase will leave the enemy unprepared in the worst case, they will fall to their death.
Unless they are powerful people like seventh-grade combatants, most flying people will pull without any resistance. Furthermore, the longer the trap is activated, the higher its pulling range.
As the altitude gets higher, its range is also bigger. It has a similar principle to a black hole in Angus' past life. A coin size black hole could pull an entire earth into the abyss. The source of pulling may be small, but the pulling range is getting bigger as time passes.
