Perpeptual Motion Machine

January 12th, 2012 by Potato

Another perpetual motion machine scheme has cropped up, this time stealing its name from a popular carnival ride, the gravitron. What made this one come to my attention was the fact that they are looking to hire a post-doc to run some calculations for them.

Now, I need a job, so I’m tempted to apply (though I have no desire to go to BC — perhaps I could work from home in Ontario?). If they’re going to waste their money to get someone to tell them precisely why their idea for a generator doesn’t obey the laws of physics, I suppose I’m as good a person as any to be the recipient of that money. On the other hand, perpetual motion machine pumpers tend to be flaky at best, and fraudulent at worst, so I’d have to negotiate for cash up front.

Their description of how it works is full of unit errors (using Watts for both power and energy, then comparing one to the other), and lots of dubious explanations. Rather than trying to work out where they’ve gone wrong on the physics (hey, they might hire me to do that!) let’s instead look at the economics. They say that it’s not a perpetual motion machine, because:

The Gravitron is not a perpetual motion machine, that is, it will not work indefinitely. The neodymium magnets that make up the magnet track will lose magnetic energy over time, and at some point will no longer have enough magnetic energy to lift the neodymium spherical magnets from the bottom to the top, at which point they will need to be replaced or remagnetized.

Ok, so let’s take that at face value: their not-a-perpetual-motion-physics-defying machine is just a really neat way to turn the energy in the magnetic field of a neodymium magnet into electricity. Well, obviously you can’t round-trip that or it’s again going to run into the perpetual motion problem, so the machine is going to extract less energy than it would take to re-magnetize the neodymium magnets when you’re done. The only way to work the machine then is to run it until you “drain” the neodymium magnets, throw those away, and buy brand new, fully-magnetized magnets to extract the energy from those anew. The question then becomes how much energy do you get, and how much does a replacement magnet cost?

Without spending too much time looking up the properties of neodymium and how to calculate the energy density of its magnetic field, Wikipedia provides this figure: an energy density of ~500 kJ/m3, or in electricity terms, 0.138 kWh per cubic meter of neodymium. A ballpark figure for the cost of electricity is 5 cents/kWh, so in order to be economical, they’d have to be able to source magnets at less than a penny per cubic meter. I don’t think so.

A former classmate says on facebook:

Here is some free advice to all inventors out there: if you have to include an explanation on your web site why your invention isn’t a perpetual motion machine, you’re probably trying to invent a perpetual motion machine.

When I told Wayfare I was thinking of applying, since hey, if nothing else I need to do some mock interviews to get some practice, she said: ‎”When I say you need to do a mock interview, I don’t mean an interview where you mock the interviewers.”

One Response to “Perpeptual Motion Machine”

  1. Marty Samson Says:

    Another perpetual motion machine.

    What do you think of this one?