how exactly would i detect if a part has landed on the ground?

I'm trying to make a pseudo 2d game on Roblox and I need to make a player system but avoiding the humanoid instance as that was made more for controlling 3d games so I need to make my own player controller, left and right I can handle myself but with jumping I need to know when the player lands on the ground so I don't have my player flying around, using a humanoid would make this easy but again I'm trying to avoid using it so I can have more control on the movement, how exactly would I make a system to detect if the player object has landed on the ground?

I don't think theres a simpler way to do this. But you could possibly name all parts that are the floor, to "Floor". Then detect when the right leg touches one of them after a jump. I don't know how exactly you would setup the code but its just an idea.