Faraday ‘s Law of Induction describes how a magnetic field interacts with an electric circuit to produce an electromotive force. It is the fundamental principle behind both electric motors and generators. An important aspect of this is Lenz ‘s Law, which states than when an induced current flows, the resulting magnetic field will always oppose the change that produced it.
Magnetic resonance imaging (MRI) machines produce a strong magnetic field along the central bore where the patient resides. This particular machine has a static magnetic field strength of 3 Tesla, which is approximately 100,000x stronger than that of the Earth’s.
When a piece of aluminum (a non-ferromagnetic metal) is moved through the MRI machine’s magnetic field, it induces an electric current in the metal. Per Lenz’s Law, the magnetic field produced by this induced current opposes the original movement and results in the aluminum slowly falling over.