There’s a fundamental truth of nature that is not often quoted. Maybe because it’s simply stating the obvious, or because it’s implicit in some of the established laws of physics and we don’t need to hear it put so plainly, I don’t know. But anyway, here it is: Everything that lives, dies and everything that’s put together falls apart. Acceptance is mandatory. We do not question why time moves only forward; why we grow older and not younger; and why a once gleaming new truck needs a bit of renovating after a decade or so. We would not expect a broken cup, its pieces lying on the kitchen floor, to suddenly mend and rise to the table from which it fell. A hot kettle will always cool. That’s the way life is. But what lies behind probably the most important of all universal truths? The answer is energy, the controlling factor that gives irreversible life in this world. To appreciate how, you just need to look a little more closely at what you already know to be true.
If I were to ask you to push a small car the length of a perfectly smooth and level track, you would probably succeed, eventually. If I then starved you for a few days and ask you to try again, you would probably collapse with exhaustion before hardly any work was done. You know the reason why: without food your muscles are not able to do work - your body’s engine needs fuel. This is also true of vehicles, of course, the very reason we sometimes end up pushing them; without fuel they don’t work either. But what is the connection between fuel and work, and why do engines and people get hot when they work? The answer again is to be found with energy, and for a description of its importance we have to look to the laws of physics.
The First Law of Thermodynamics states that energy is always conserved; it cannot be created or destroyed. This is true of all systems, large or small. The universe contains a finite amount of energy, energy that is continually transforming from one form to another. Like all stars, the Sun burns fuel and in doing so converts chemical energy to heat and light; plants convert light back to chemical energy. Plants provide the fuel that starts the food chain, a chain of energy that eventually fuels us. The oil that is the remains of ancient, long dead plants provides the chemical energy that fuels most of our machines. And the energy this fuel puts into our vehicles is converted to heat energy and kinetic energy, the energy of motion. When we brake, kinetic energy is exchanged for heat energy, as the vehicle slows.
Energy is the ability to do work, and work is a product of force and distance. This may sound a little complicated until you remember what you would instinctively do if the fuel gauge on your car went into the red and you still had a little way to travel. If you drive fast you will use more fuel. At higher speeds the rolling resistance of tyres, a force that is trying to slow you down, is greater. As is the friction force in all the moving parts between the engine and the road wheels. And, of course, so is air resistance, which greatly increases with increasing speed. All these forces have to be counteracted by the engine, which provides the force to keep you moving. So, you drive more sedately, keeping the engine revolutions to a minimum. For the amount of energy available in the fuel, reducing the force required from the engine allows you to eke out more distance.
Energy not only fuels us and our machines, it is also responsible for giving those that can use it the power to be quick. Power is the rate at which energy is used, and the faster you can use energy the more powerful you will be. Large sports motorcycles are a classic example of how to use energy quickly. With over-square pistons, these high revving, short stroke gas guzzlers do loads of work. With a great power to weight ratio they explode with acceleration and overcome retarding forces to give extremely high speeds. Trucks also use power, but to provide the level of work needed to deal with the high retarding forces caused by their weight. Through higher torque and longer stroke engines, they attempt to limit engine revolutions while maintaining speed. High powered trucks climb hills well.
Because energy gives life, it can also save it. In a collision cars are designed so that energy is converted from that of motion, which is ultimately the killer, to a less harmful form. By collapsing in a controlled way, car structures do work, dispersing kinetic energy. Work is done over a specific distance to reduce the force for a given amount of energy. The reduction in force that results gives life.
When work is done heat is produced, the result of another fundamental law of physics. The Second Law of Thermodynamics says that in any system the energy available to do work is always diminishing. Our bodies and our vehicles only convert a certain amount of the chemical energy in fuel to kinetic energy; the rest goes to heat energy. When we work, we get hot. The Second Law works against us in the efficiency of engines, which will never be allowed to reach 100%. Tyres generate heat that will eventually destroy them; bearings and pistons wear out. It is always the same. If you drop a rubber ball from a certain height it will never bounce back to your hand, not unless you lower the hand to meet it. Internal friction in the ball as it bounces creates heat, so the potential energy given to the ball by the height it was dropped from is never fully regained. A cyclist that free-wheels down a hill will not have sufficient useable energy to climb back up a hill of the same height. They would eventually have to put more energy into the system by pedalling.
And as useable energy diminishes, like a kettle that cools until it is the same temperature as the air that surrounds it, in time everything assumes a position of energy equilibrium, a condition where it is most stable but least able to do work. Materials manufactured from elements in their natural state eventually return to that state. Metals corrode, plastics degrade. Ashes to ashes, dust to dust. Everything dies; it has to, the rules say so.
So, next time you drive your car, think of all the energy changing from one form to another as you travel along. Chemical energy to kinetic energy to heat energy. And think of yourself, how your breakfast is turning the steering wheel and pushing the clutch. All the while both you and the machine are heading in the same direction in space and time, your mechanisms wearing down. When you get home, be sure to plug in the kettle and rest while you can, because summer’s coming and the outside of the house will probably need painting – again.
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