Elementary Kinematics: The Lens-Magnet-Spinner of WaxingRadiance

This True Experiment contains all the data you need to understand how and why the upper object spins, and allows prediction of direction of spin.

Only one of the objects needs to be a magnet. A smooth flat piece of ferromagnetic metal will act just the same, in either the top or bottom role. And will spin in the same relative direction.

The upper object here isn’t even a metal or ferrite magnet. It is one of those flexible “rubber magnets” that comes in sheets and is magnetized by a process analogous to recording a magnetic tape, with gapped heads and all.

The point of contact of the upper object with the curved surface of the lens is a “drag point” and the attractive force of the magnet and the gravity of the earth create a force couple with this drag point and thus result in the rotational motion of the object, with the drag point as the pivot. The entire process can be duplicated without any magnets at all. I leave the design of the apparatus as an exercise for the reader.

You might want to review your Beer & Johnston first, if it’s not immediately obvious.

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Music is “Get Back” by Silent Partner, from the YT Audio Library. Thanks folks!

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