The Capillary Water-Wheel.

The world, we are told, is in the grip of a growing energy crisis. This of course is not accurate- there are any number of energy sources available, it just requires a little ingenuity to tap some of them. To illustrate this point, I have devised a perpetual motion machine.
Of course every moderately attentive schoolboy knows that prepetual motion machines in the strictest sense are impossible, as they violate the first law of thermodynamics- you cannot create energy. Perpetual motion by harnassing the forces of nature however, is less of a challenge; for example, James Cox famously developed a perpetual clock powered by variations in atmospheric pressure. ( http://en.wikipedia.org/wiki/Cox )
My device works on the principles of capillary action and gravity. Capillary action is really a manifestation of surface tension which allows liquids, in this case water, to climb porous materials. In this device, a length of porous material is immersed at its base, in a trough of water. The water obligingly climbs this, and from the top of it is soaked into a seperate piece of porous substance attached to the paddles of my water-wheel. When the weight of water becomes sufficient, the paddle falls, turning the wheel and bringing the next paddle into place to repeat the process. Upon falling, the orientation of the 'sponge' on the paddle changes from horizontal to upright, reducing its capacity to hold liquid. Most of the water thus drains back into the trough below, rendering the paddle light again. The result is a perpetual turning motion, as illustrated above. The total energy output from such a contraption is inadequate for many practical uses, but working out whence the energy comes is a diverting challenge.