A sample text widget

Etiam pulvinar consectetur dolor sed malesuada. Ut convallis euismod dolor nec pretium. Nunc ut tristique massa.

Nam sodales mi vitae dolor ullamcorper et vulputate enim accumsan. Morbi orci magna, tincidunt vitae molestie nec, molestie at mi. Nulla nulla lorem, suscipit in posuere in, interdum non magna.

Perpetual Motion Revisited

On our most recent 5×5 episode we discussed the notion of perpetual motion, or free energy machines. They are, as anyone who is even vaguely familiar with the laws of thermodynamics and conservation is aware, impossible. The bottom line is that there is no way to create a machine that created energy from nothing. Energy always has to come from somewhere, and at least a little bit of energy has to be wasted in any process.

However, listener Karen Clow (rhymes with “flow”) asks this question:

I just listened to your 5×5 episode about perpetual motion, and I have a question.  While I haven’t been able to find it on YouTube, I saw a video a few months ago that seemed like a form of perpetual motion.  There was a column of marbles in the center, and the structure holding the column was slightly wider than the marbles so that instead of a straight-up stack, they rested on top of one another in a sort of zig-zag pattern.  There was a “track” of sorts starting form the top of the column, so that a marble went down the track, and when it reached the bottom, it went into the bottom of the column, forcing the column up, causing the top marble to go down the track.  I don’t recall anyone claiming that this was perpetual motion in the traditional sense, it was more of a “kinetic art” thing (although searching for kinetic art I can only find pieces which use motors).  I also realize that there would be no way to harness the energy of the marbles, since any attempt to do so would cause them to slow down enough that they wouldn’t have enough inertia to force the column upwards.  Is my memory of this invention flawed?  Is such a thing possible, and if so, would it not be considered perpetual motion?  Sorry if this is a hoax that’s been debunked a hundred times over, but nothing about it seemed to be an attempted hoax, it was more of a curiosity like a fountain but with marbles instead of water, so I’m really curious.

These types of machines are not the free energy machines that we were talking about.  As Karen points out, they cannot be used to generate energy. If you try to take energy out of the system it will quickly wind down. But can you make a machine that is energy neutral – meaning that it does not create energy but it does not lose energy either, so it can continue indefinitely – perpetual motion?

Here is one such device:

The trick to this type of perpetual motion is to eliminate all sources of energy loss – usually friction. Imagine the earth revolving about the sun – this is a type of perpetual, or at least very long-lived, motion. There is little friction is space and the momentum of the earth is precisely balanced by the gravitational force of the earth-sun system so that it is very stable. It is probably more accurate to describe this as a very stable system, rather than perpetual motion, but billions of years is pretty good.

On earth it is more difficult to create a micro-friction situation. A rolling marble makes noise; that noise represents vibrating air molecules, which takes energy. Therefore noise is carrying energy away from the system. There is also friction with the air, and vibrations in the machine itself. So while a precisely engineered machine may minimize friction and other subtle energy losses, it cannot eliminate it completely.

Therefore most of these perpetual motion machines use another trick to simulate true perpetual motion – they are tapping into a subtle source of energy to replace the slight loss in the system. These are often very clever. Magnets may be used to give a ferromagnetic component a subtle push, just enough to replace losses due to friction. Of course, this takes energy away from the magnet which will eventually wear down. It seems like the machine above may be using magnets.

However, that machine also has pendulums. It is therefore possible that energy could be borrowed from the rotation of the earth, which would make free swinging pendulums rotate around (ala Foucault).

I have also heard of a clock that is wound by the expansion and contraction of various metals in the spring from the daily cycle of heating and cooling in the room. Watches that wind by the motion of the wearer are now old hat, but that is another example.

The fact is, there is lots of usable energy in the environment. If you could tap into some source of energy, even if it is slight, it can potentially keep a precise system going indefinitely (as long as the conditions and materials remain stable). On a large scale such systems may even be used to generate usable energy. I have heard plans for sidewalks that derive energy from the people walking on them, or piezoelectrical systems that generate electricity from the energy of raindrops falling on them. In the new era of supposed green energy, most people have probably seen proposals for generating energy from ocean waves.

It is fun to think about the ultimate sources of energy on the earth – mainly solar, nuclear and geothermal. The sun heats the surface of the earth putting a lot of energy into the system, which causes the wind to blow, runs waterfalls, and gives energy to plants (the ultimate source of all fossil fuel energy). Radioactive minerals provide energy through nuclear reactors. And the earth itself is very hot beneath the surface – energy deriving from all the collisions that formed the earth.

There is another potential source of energy – the gravity of the moon and sun, which cause tides, which could be tapped for energy. There are also many sources of chemical energy, although I am not sure how much of that derives from other sources like solar and geothermal. And naturally occurring magnets have energy, but again I am not sure where they ultimately get their energy from – from the collisions that made them or from the supernova that formed the elements themselves (which is the ultimate source of nuclear energy).

I have probably missed something. If you can think of any other ultimate sources of energy that we could potentially tap into, let us know in the comments.

2 comments to Perpetual Motion Revisited

  • Drum Billet

    How about tapping the energy from a black hole?

    The Time Lords did it, so I don’t see why we can’t.

  • The ever-present neutrino flux is another source of energy.
    Let’s see the con-artists use that!
    Plus: Cosmic rays, the Casimir effect, sound (did you explicitly cover that one?), photon pressure, to name but a few.

Leave a Reply