How could you make a bobbing "animation" for an object?

I have floating swords with SurfaceGUIs in front of them that the player can interact with to buy and / or sell, but right now they feel kind of static just sitting there (and being anchored). To give more life and movement to them, I wanted to program something that would make them bob up and down so they would be "floating".

Looked into it for a bit and would assume it has something to do with CFrame but I couldn't find a definitive answer and I couldn't figure out how to do it myself. Any pointers people could give me would be appreciated.

tl;dr I want to make something bob up and down as if its floating but cant find out how to do it myself. Need a shove in the right direction.

If you have any questions please feel free to ask in the comments.

Inside anything that is called per frame you can use this formula:

local pos = Origin + Vector3.new(0, math.abs(math.sin(P + DT * S) * amplitude), 0)
--// where p is phase, dt is deltatime, and s is speed.
--// i had this formula saved from the devforum.

You can also use TweenService to gradually move it up and down.