Section 1.5 – Energy
Outline of the Work, Energy, Wealth and Power thread:
In 1865, economist William Jevons remarked that in about 100 years the British coal reserves would be exhausted, and that this would mean the end of Britain’s dominance as a major world power. This must have seemed inconceivable to his readers at that time – at the height of the wealth and confidence of the greatest global empire the world had ever seen, but – as we know now – it was uncannily accurate. By 1965 most of Britain’s coalfields were nearing exhaustion, and its time as a leading world power was indeed over.
In the previous section we touched on the fact that creating wealth involves work. Energy is what it takes to get work done. The energy to do the work of getting your car from one place to another comes from the gasoline that you put in the tank. The energy to run your sewing machine comes from the electric current flowing from the wall socket. The energy to dig your vegetable patch comes from the sugar in your muscle cells causing them to change shape (the actual biochemistry is more complicated than this, but this is accurate as a summary).
Let’s trace this further back: the energy in the sugar came from the food ate you ate for dinner. The energy in the vegetables came from sugars that were manufactured in the leaves of the plant from energy in the sunlight. The energy in the sunlight came from the fusion of hydrogen into helium in the core of the sun (the same process that releases energy when a nuclear warhead is detonated). The energy in the meat came from plants that the animal ate.
The energy in gasoline is derived from sugars manufactured by marine plankton and other micro-organisms millions of years ago from sunlight that fell on the Earth at that time.
The energy that is delivered from your electric sockets came from the movement of spinning magnets within coils of wire in the generators in the power station. The magnets were spinning because they were connected to turbines driven by high-pressure steam. The energy in the steam came from coal burned in the boilers, and the energy in the coal came from sugars made in the leaves of trees in ancient forests, from sunlight which fell on the Earth between 300 and 360 million years ago.
But suppose the electricity was generated in a nuclear power station? In this case the heat for the steam to drive the turbines came from the breaking up of uranium nuclei into smaller lighter elements. This energy was originally stored in the Uranium by nuclear processes in the centre of stars that lived and died before our sun and solar system were formed.
From these reflections we can draw two conclusions: the first is that energy can take many forms and can be changed from one form to another myriad ways. Careful experiments carried out over the last few hundred years have established that in every conversion process the total amount of energy at the end is exactly the same as it was at the start. This is the First Law of Heat and Movement (it is usually called the First Law of Thermodynamics, but as with other technical jargon elsewhere in the book, I’m going to substitute words in everyday language. ‘Thermodynamics’ sounds complicated, mysterious, difficult – but it’s just a fancy way of saying ‘heat and movement’, and if I use those words you will know what I’m talking about). Another name is the Law of Conservation of Energy.
When you are driving down the road, some of the energy consumed from the gasoline taken from your fuel tank has took been turned into the energy of the movement of your car, but not all of it. Some has been turned into heat energy making the engine hot; heat warming the air passing through the radiator; and heat in the gases emitted from the exhaust pipe. When you bring the car back to a standstill all that energy of movement is turned into heat energy in the hot brake discs and the air around them. – Unless you have an electric or hybrid car, in which case some of that would have been turned into electrical energy and stored in the battery, in the form of chemical energy.
The second conclusion is that although the total quantity of energy remains constant, the quality of it does not. You cannot use the heat that was dissipated into the environment from the radiator and the exhaust pipe and the brakes to drive back home again! This observation is the basis for the Second Law of Heat and Movement, and it is the reason why it is impossible to build a perpetual motion machine.
In everyday usage the words energy and power are used more or less interchangeably, and many people are uncertain of the distinction between them. But to an engineer, the concepts are clear: energy, as we have said, is the capacity to do work, whereas power is the rate of doing work (or the rate of transforming one form of energy into another). It takes the same amount of energy to boil a litre of water whatever the power of your kettle, but a 3 kW kettle will do it in one third of the time that a 1 kW one would have. A 300 hp sports car will accelerate to 60 miles an hour about six times as quickly as a 50 hp family saloon of the same weight.
There is of course another – somewhat related – meaning of the word power: the ability to control or exploit the actions of others, as in political or economic power. Political power depends on economic power, and – as human affairs are ordered currently – both are derived ultimately from military power. Hence the relevance of Britain’s ability to operate a global empire being dependent on the energy supply from its coalfields. And hence the conflict today over control of the world’s oil supplies. The Work, Energy, Wealth and Power thread will explore these issues in greater depth, and examine their interactions with the other threads.
This is Section 1.5 of my forthcoming book The World in 2100: What might be Possible for Humanity?
When we return to the ‘Work, Energy, Wealth and Power’ thread, the next topic will be The Second Law – and Why You Cannot Build a Perpetual Motion Machine.
If you haven’t already done so, you can register to receive a free review copy just before it goes on general sale later this summer. Registering will also take you straight to Chapter 1 – The Foundations which will give you more idea of what the book will cover.
