“Perpetual” machines consume more energy than they generate

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

20 May 2007

We are very good at counting money – making sure that we trace how much we put into a project and how much we get out of it. Although that reminds me of a person who started a business (selling groceries) and he could not make out how much profit or loss he was making from the enterprise!

When it comes to energy, most people assume that it cannot be quantified accurately, even though they “know” that a lorry, for example, produces more energy than a car. Thus, many readers were convinced that the invention I described here last week can work. Out of 14 letters, only one (Nathan Ateka Mukaka of Webuye) gave proper reasons why the perpetual machine wouldn’t run; the rest encouraged me to look for funds and build it!

So, let us analyse it. Suppose that each litre of water flowing from the top to the bottom tank generates ten units of energy. Assume further that all the bearings, pipes and joints are 100 percent smooth – that is, they present no resistance to the movement of shafts and water.

Now, it is obvious that the amount of energy generated by one litre of water flowing from the top tank to the bottom one is exactly equal to that required to pump one litre upwards. Therefore, the idealised, 100 percent smooth machine can run for ever. But what happens when the electricity generator is connected?

It will convert some of the energy into electricity - say, 20 percent. So, when one litre flows down, ten units of energy are produced. Out of these, 2 (20 percent) are converted into electrical power and only 8 are left for the job of returning water to the upper tank.

If ten units of energy can pump one litre of water, then 8 units can only pump 0.8 litre (800mL). Therefore, every time one litre flows down, only 0.8L will be pumped up. Thus the volume of water in the lower tank will increase while that in the upper one will decrease. Eventually, the flow will reduce to just trickle – not even enough to turn the generator.

Now, if that is what would happen in an ideal, 100 percent smooth system, imagine how a real one with normal bearings and pipes behaves. The friction can take away another 25 percent of the energy. Add to that the fact that the electricity generator will also waste another 5 to 10 percent and it turns out that only about half of the energy will be available to pump the water back to the upper tank.

Thus the system slows down continuously and, in a short time, the excess water in the bottom tank has to be pumped up by some external means. This is the case with all perpetual motion machines: They need an external injection of energy to start them off and periodic additions to keep them running. They are not “perpetual”! In reality, they actually consume more energy than they generate.