The magnetic field of the earth can rotate a flat coil in its plane. This is explained in Earth’s magnetic field and parallel action. Will a disc magnet rotate a flat coil the same way? The magnetic field of a disc magnet is central symmetric and the field lines are contained in median planes (See Figure 1). If a flat coil is coplanar with a median plane, the Lorentz forces on the currents will be perpendicular to the plane of the coil. So, Lorentz force could not rotate the flat coil in its plane. But in my experiment the coil rotates.

Please read the article at
Disc magnet parallel action experiment
http://pengkuanem.blogspot.com/2015/06/disc-magnet-parallel-action-experiment.html
or Disc magnet parallel action experiment (video included)
https://www.academia.edu/13033082/Disc_magnet_parallel_action_experiment_video_included_

Earth’s magnetic field and parallel action

The magnetic field of the earth is uniform on its surface. The resultant Lorentz force a uniform magnetic field exerts on a coil of any shape is zero. The torque perpendicular to a flat coil is also zero. So, a current carrying coil in the magnetic field of the earth should stay immobile. However, my experiment shows that the test coil rotates in its plane. See the video of this experiment: http://youtu.be/JKMG8jY1RRg

Please read the article at
Earth’s magnetic field and parallel action
http://pengkuanem.blogspot.com/2015/06/earths-magnetic-field-and-parallel.html
or Earth’s magnetic field and parallel action (video included)
https://www.academia.edu/12926460/Earth_s_magnetic_field_and_parallel_action_video_included_

In “Q: Parallel action with a solenoid” I have asked a question: the magnetic field of a long solenoid being zero, will it make a coil rotate in its plan? This experiment will investigate the parallel action of a long solenoid. I have done this experiment and here is my result.

Please read the article at
Solenoid parallel action experiment
http://pengkuanem.blogspot.com/2015/06/solenoid-parallel-action-experiment.html
or Solenoid parallel action experiment with video included
https://www.academia.edu/12722675/Solenoid_parallel_action_experiment_with_video_included