In many ways, physical mediumship does adhere to the laws of  physics.  Here, we see the production of  what is known as ectoplasmic rods.  It is through the production of  these rods that levitation often occurs.  Generally, the rods are constructed from an invisible form of  ectoplasm.  William J. Crawford spent many years investigating the Goligher circle  (Kathleen Goligher, the medium).  Through his researches, he ascertained that spirit uses these rods very much like a cantilever in order to apply the necessary force to levitate an object.  His findings can be found in the book,  "The Reality of  Psychic Phenomena:  Raps, Levitations, Etc.",  by W. J. Crawford.