Most of the science I learned at school was reasonably straightforward – I understood it and accepted it, and most of the time remembered it too. Except for potential energy, which never made any sense whatsoever. In fact, I recently told a teacher friend of mine why potential energy doesn’t work, and he couldn’t counter my argument. The following is therefore my thought process in trying to understand and/or disprove potential energy, and may or may not actually include anything scientific.

Ok, the idea of potential energy is that if you raise an object to a certain height you have given it potential energy – you have used energy in raising it, and since energy cannot be created or destroyed but only transformed from one form to another, the energy you used in moving it upwards must then be stored in that object as potential energy. At least, that’s what the textbooks told us. Where it falls down is where you measure that distance from. If you lift a book off the table, where it is at rest, and put it on a shelf, you have raised it 1m, for instance. That apparently gives the book a certain amount of potential energy. If you drop the book from 1m it will use that amount of energy in the falling process. What happens if you move the floor? What happens if you move that book left a bit and drop it out of the window, you happen to be on the top floor of a very tall building? It’s not the object that increases its store of energy, but the world around it that changes in relation to it.

Now we can see from this that potential energy cannot possibly be just to do with the distance between the object and the ground, because we cannot define what the ground is. It might be a table, but the table might be on the top floor of a building, and the building might be on a hill. No, this all comes back to gravity, and hence the distance from the centre of the earth. The further something is away from the centre of the earth, the more potential energy it has. However, the earth is not the only gravitational force we experience – the sun is a pretty strong contender too. If the earth suddenly vanished (we’re not necessarily in the realms of science here) we would be floating around in space, and the force of the sun’s gravity would pull us toward it. That means that right now the sun is still pulling on us, and since we are millions of miles from the centre of the sun, that should warrant us an enormous amount of potential energy. Then take into account all the suns and all the planets in the universe, and we should have an almost infinite amount of potential energy, which makes no sense at all since we can’t use it.

The next problem is that gravity decreases the further away from the source you are. I can’t be bothered to go drawing graphs and playing with algorithms to work out the relationship there, I’ll let someone who actually knows about this sort of stuff do that!

Ok, let’s go back to our book on the shelf. Gravity is pulling it downwards, and in order to keep the book in one place the shelf must therefore be exerting an equal force in the opposite direction. Does that take energy? Does the shelf use energy? I can’t possibly be using energy, since it has no energy source, it’s a shelf. Neither is the floor using energy to hold up everything sitting on it. Which tends to imply that gravity is not an energy either, but only a force. Gravity is generated by mass and movement. Ah, now we also get kinetic energy into the equation – if movement is energy, gravity does indeed have energy to transform, and gravity is a form of energy. But is kinetic energy really energy? If I’m sat on a chair, I’m not moving. The chair is not moving relative to the room, the room is not moving relative to the house, the house is not moving relative to the country, but the planet is most definitely moving around the sun, and the sun is moving around the galaxy, and the galaxy is moving around the universe, and so as I sit on the chair I am actually moving incredibly fast. Does that mean I have loads and loads of kinetic energy? Not really. If you have a book in space and you set it moving relative to the universe, unaffected by external forces it will continue to move in that direction indefinitely, neither increasing or decreasing in speed. It’s moving, but is it using kinetic energy? If it is using energy, where is that energy coming from, and will it run out? Now I’m beginning to think that kinetic energy doesn’t exist either, in which case mass and movement create gravity but not energy.

Potential energy is therefore not an energy in itself, but more an equation-balancing trick used by physics teachers to try to persuade us that it makes sense, when it clearly doesn’t. If a book is on the shelf it has the logical potential to fall, hence ‘potential’ energy. As it falls it moves, which is ‘kinetic’ energy. When it hits the floor the floor exerts an equal and opposite force to stop the book in its tracks, but we don’t attribute the floor as using energy to counteract the momentum of the falling book. Lifting a book in our hand requires us to use energy, we can feel our muscles working against the weight of the book. For us to keep the book stationary at a certain height we have to maintain that force, which requires us to use energy. The longer we hold the book there, the more energy we use. Where is all that energy going? Is the book more potentially energised the longer we hold it there? No, it’s just a book. I therefore submit that energy is being used to create force, and that it isn’t transformed into potential energy, nor is potential energy transformed into kinetic energy, and hence science is wrong.

Categories: Rants


Phill · 23 June 2007 at 6:32 pm

Energy… it’s all relative, innit? 😀

Dad · 25 June 2007 at 10:04 am

You should get out more, Matthew!!

Matthew · 25 June 2007 at 10:22 am

Out? Out? I was out when I thought of all this!!

Just the thought of all that kinetic energy I supposedly have as I wizz round the universe on this little planet is enough to make me feel dizzy…

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