Answer :
The process of PLACING a compass wherever you want it involves Biology. Biology deals with everything that has to happen for your brain to send instructions to your muscles, your muscles to operate your arm and your hand, and your hand to move the compass to where you want it, while your eyes keep track of what's happening and send course-corrections through your brain.
Once you get the compass there and see it start doing strange things, those EFFECTS are explained by laws of nature that are covered in Physics.