Have you ever seen a wheel rolling uphill, neglecting the laws of gravity? You can by realizing this interesting desktop gadget.
A small neodymium ring magnet (d=10mm, t=5mm) is attracted by a row of ten even smaller (5x5x5mm) cubes, hidden under a rail.
http://www.supermagnete.nl/
Make sure the orientation of the cubes is correct. The easiest way is to take the ring magnet between two fingers, and bring it in contact with one cube. The cube will position itself and can be pushed into its hole with the ring magnet. Repeat this for the other nine cubes without changing the orientation of ring magnet and rail. The climbing angle of the rail is about 20 degrees. If the ring stops halfway, the distance to the cubes is too small. There should be a layer of about 4mm between the ring and the cubes.
The ring magnet is placed at the bottom and then released. It will run uphill right to the top.
Suppose, we can shoot the ring magnet beyond the last cube and let it roll down to the start position, driven by gravity. Wouldn’t that be a perfect perpetuum mobile? Too bad there is an equilibrium law.
https://www.youtube.com/watch?v=74LaGS8pPy4&feature=youtu.be

https://www.youtube.com/watch?v=G7McaP5eJx8&feature=youtu.be