The Way Things Work Now
INTRODUCTION EVERYTHING A MACHINE DOES is in accordance with a set of principles or scientific laws. To see the way a machine works, you can take the covers off and look inside. But to understand what goes on, you need to get to know the principles that govern its actions. The machines in this and the following parts of this book are therefore grouped by their principles rather than by their uses. This produces some interesting neighbours: the plough rubs shoulders with the zipper, for example, and the hydroelectric power station with the dentist’s drill. They may be vastly different in scale and have different purposes, but when seen in terms of principles, they work in the same way.
MACHINERY IN MOTION Mechanical machines work with parts that move, including levers, gears, belts, wheels, cams, cranks, and springs. These moving parts are often interconnected in complex linkages, some large enough to move mountains and others almost invisible. Their movement can be so fast that it disappears in a blur of spinning axles and whirling gears, or it can be so slow that nothing seems to be moving at all. But whatever their nature, all machines that use mechanical parts are built with the same single aim: to change the size or direction of a force.
MOVEMENT AND FORCE Many machines convert one form of movement into another. Often linear movement is converted into circular or rotary movement, and vice-versa, because the power source driving the machine moves in one way and the machine in another. But whether direction is altered or not, the mechanical parts change the force applied into one – either larger or smaller – that is appropriate for the task to be tackled. A force may be the push of a motor, or the pull of muscle or gravity, for example.
A machine changes the size of this force and conveys it to the right place to do a job. When you squeeze and twist the handles of a can opener, the blade cuts easily through the lid of the can. This makes light work of something that would otherwise be impossible. The can opener increases the force that your wrist produces and applies it where it is needed.
THE CONSERVATION OF ENERGY Underlying the actions of all machines is one principle which encompasses all the others – the conservation of energy. This principle says that you can only get as much energy out of a machine as you put into it in the first place – no more and no less. Energy takes different forms. Movement is a form of energy called kinetic energy. It is produced by converting other forms of energy, such as the potential energy stored in a spring, the heat in a petrol engine, the electric energy in an electric motor, or the chemical energy in muscles. A machine can only expend the same amount of energy as that put into it to get things moving. If the force the machine applies is to be greater, then the movement produced must be correspondingly smaller, and vice-versa. Overall, the total energy always remains the same. The principle of conservation of energy governs all actions. Springs may store energy, and friction will convert energy to heat, but when everything is taken into account, no energy is created and none destroyed. If the principle of conservation of energy were to vanish, then nothing would work. If energy were destroyed as machines worked, then, no matter how powerful they might be, they would all slow down and stop. And if the workings of machines created energy, then all machines would get faster and faster in an energy build-up of titanic proportions. Either way, the world would end – with a whimper in one case and a bang in the other. But the principle of conservation of energy holds good and all machines obey: energy cannot be created or destroyed, only converted into different forms.
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