How do you make objects realistically jump and fall?

So, I was going to make something like one of those fireballs from Mario, and I was using BodyPosition to try to essentially mimic the jumping and falling of them, but I couldn't get the gravity right.

local fireball = script.Parent
local a = fireball.Parent.A
local b = fireball.Parent.B
local c = fireball.Parent.C
local bodyPosition = fireball.BodyPosition

while true do
bodyPosition.Position = a.Position	
	wait(5)
	fireball.Transparency = 0

bodyPosition.Position = c.Position
	wait(.6)	
	bodyPosition.Position = b.Position
	wait(0.01)
end

That's the script, am I doing something wrong? Should I use one of the other bodymovers?