The motor spins the copper disk to a high speed. Then by pushing the magnets (red) over the disk, the disk is caused to stop very quickly. Almost no parts to wear out.
This device was on display at the International Tesla Society Museum, for its demonstration of the electromagnetic principles involved.
The usual explanation is this: When a conductor moves through a magnetic field, the electrons in it are made to move (of course), and when they move they generate their own magnetic field which is opposite to the external magnetic field that is causing them to move (Lenz law), resulting in direct repulsion, and therefore opposition to movement of the conductor. (I would welcome new or different information on this).
gee_ha_double_u_kay_at_this_server_dot_com
Date: Thu, 22 May 1997 07:01:04 -0700 To: gee_ha_double_u_kay_at_this_server_dot_com Subject: Magnetic Brake --- Comments --- Sounds a lot like the dynamic brake systems used in diesel locomotives and heavy mining equipment using electric motors for traction. When the brake is applied it redirects the current to the motor turning it into a generator and the power produced is disipated in electric grids.