• Question: Is faeces a form of energy and does it adhere to the laws of conservation of energy?

    Asked by mustumar to Chris, Dave, David, Fiona, Jack on 25 Jun 2013.
    • Photo: Jack Miller

      Jack Miller answered on 25 Jun 2013:

      Hi mustumar,

      Everything that can happen in our universe conserves energy overall. What you decide to do with your poo, and how you do it, is limited (ultimately) by how much energy is in it, and how effective you are at extracting that.

      The most obvious source of energy in faeces is chemical: many people around the world heat their homes by burning it. Faeces is a complicated mix of organic molecules, bacteria, water and other elements in smaller quantities, so you can get a fair amount of energy out by burning it, removing carbon and producing CO2.

      If your sample of faeces was moving relative to an observer, it would have kinetic energy in his frame of reference (and the observer would have kinetic energy in the poo’s reference frame). There is no limit, in principle, to the amount of kinetic something has, although practical constraints — such as the Earth’s atmosphere, the ease at which you can accelerate an amorphous block of faeces, and the amount of energy in the universe — do limit how much energy you could ever impart. Naturally, the poo would asymptotically approach the speed of light as you fed more and more time and resources into accelerating it.

      If you decided to hold your faeces and swing your arm about in a rotational fashion, you and your poo would have angular momentum. The behaviour of things that rotate is different to things moving in a straight line: anything moving in a circle is constantly being accelerated. If you opened your hand, most of this rotational potential energy (given, in total by E=1/2 I omega^2, where I is the ‘moment of inertia’ of you and your poo, and omega your rotational frequency) would be converted to kinetic energy, and you’d successfully fling your faeces everywhere (at a wall, your keepers, your disgusted parents, etc).

      By far the most energy faeces has, however, is that due to its mass. The total amount of energy bound up in particles like protons, neutrons and electrons is unimaginably huge — for poo that isn’t moving in your reference frame, it’s just given by mc^2. (For poo that’s moving with a certain momentum, E^2=p^2c^2-m^2c^4). If you could release all of this energy at once, you’d probably blast a chunk out of the side of the earth — even thermonuclear fusion weapons only release the difference in binding energies between certain atomic nuclei, not all of the energy of those nuclei’s total mass at once.

      In fact, assuming you somehow managed to utterly annihilate a fairly substantial 200g block of faeces, the total amount of energy released would be about that of the meteor impact that led to the extinction of the dinosaurs. Now, that really would be an explosive time on the toilet!

      Hope that helps,

      — Jack

    • Photo: Dave Farmer

      Dave Farmer answered on 25 Jun 2013:

      There’s no way I can compete with Jack’s answer, clearly he puts his time on the toilet to good use!