How to find position between a part and a player?

1. use magnitude!

You shouldn't be defining getMagnitude yourself. ROBLOX has it built in. (In general, you should pretty much never need to use .x, .y and .z on a vector)

part_position.magnitude

2. update your variables!

You only ever set (ie., change) the Position and part_position variable at the beginning of the script.

That means if the player moves, Position isn't going to change. You have to explicitly ask for the position of the player each time you need it to be fresh.

Part.Position.magnitude - Torso.Position.magnitude

3. compute distance correctly!

The difference of magnitudes is not the way to measure the distance between things. (That clearly doesn't make sense. Magnitudes are numbers; a difference could be negative -- what is a negative distance? Magnitude of a position is also meaningless, because it makes the origin special).

The magnitude of the difference in position is what you want:

local distance = (Torso.Position - Part.Position).magnitude

4. use while right!

You are not using while in a meaningful way. while will stop once the condition fails. Thus this will print until the player is not within five studs, and then the script is over.

What you want to do is:

• For forever,
  • if the player is close, print.

So write that!

while wait(1) do
	local distance = (Torso.Position - Part.Position).magnitude
	if distance < 5 then
		print(distance)
	end
end