Len's Law states that the direction of current induced in a conductor by a changing magnetic field due to Faraday's law of induction will create a magnetic field that opposes the change that produced it. In this demonstration, a very strong neodymium magnet falls slowly down a copper tube as though passing through a viscous liquid. Moving magnetic fields produce electric currents in a conductor, such as copper. These currents produce magnetic fields that have the opposite polarity to the initial field. So, a falling magnet makes the copper tube briefly into an electromagnet that acts against the falling magnet. Credit: PhysicsFun