The SMOT device described in Wikipedia is said to cause a metal ball to roll uphill and then fall off the ramp.

I understand that perpetual motion is not possible. However, reading through the Wikipedia talk pages and the reference given does not give me a clear indication whether the device works or not. Does the ball go up the ramp? Does it fall over the edge? What part of it "does not work?" Does it go up halfway?

I am confused as to what the laws of physics say can about the device and where exactly the laws of physics say the ball will stop, once it is placed at the beginning of the ramp.

  • $\begingroup$ Please, out of courtesy to readers, do not use unfamiliar acronyms or abbreviations without defining them on their first use. Here, that would be in the subject/title. $\endgroup$ – garyp Dec 27 '16 at 15:05

The section of your article entitled "Analysis of operation" pretty much spells out why it wouldn't (and doesn't) work. Over any closed loop, the ball cannot gain energy from the action of magnetic fields; since there is also friction, which dissipates energy, the ball must eventually stop.

  • $\begingroup$ As to where the ball stops, that's difficult to predict without knowing details such as the initial distance of the ball from the first magnet and the height of the ramp. It could indeed make several loops before stopping, if the magnets are strong and the ramp is short. On the other hand, it could also not even make it up the ramp in the opposite case. $\endgroup$ – probably_someone Dec 27 '16 at 9:27
  • $\begingroup$ The "Analysis of operation" part of the Wikipedia article says "At the starting point, the ball has the potential energy given it by being put there under the forces of the magnets". Since the article is not specific about how the ball is put in place, it does not specify the forces of magnets on the ball when it is being put to place. Presumably being rolled down the ramp against the action of the magnets would involve different forces than if it was rolled to the start of the ramp from a position where the magnetic fields are much weaker? $\endgroup$ – stackex555 Dec 27 '16 at 10:42
  • $\begingroup$ Yes, in that rolling down the ramp involves gravity. Otherwise, no. $\endgroup$ – probably_someone Dec 27 '16 at 10:56
  • $\begingroup$ The strength of the magnetic field decreses according to the inverse square law, so how can the ball experience the same force acting on it regardless of whether it is moved through a weak field or a strong field? Maybe that's another question. $\endgroup$ – stackex555 Dec 27 '16 at 11:14
  • $\begingroup$ It doesn't experience the same force, but that doesn't matter from an energy perspective. Can you give me a closed path (i.e. starting and ending at the same point) for which the ball ends up with more energy than it had before? $\endgroup$ – probably_someone Dec 27 '16 at 11:26

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.