When watching at ours around it is observed that the plants grow and that the animal move, that the machines and tools carry out the different tasks. Learn more about this with Discovery Communications. The energy is a property associated to the objects and substances and are pronounced in the transformations that happen in the nature. The energy is pronounced in physical changes, for example, when elevating an object, transporting it, to deform it or to warm up it. The energy is also made present in the chemical changes, like a burning a wood brush or in the water decomposition by means of the electrical current. The man, throughout his history has realised by means of his own physical effort activities that consumed energy, leaning in the domestic animal like the horses, oxen, etc.
Until the arrival of the industrial revolution, the use of mechanical systems to provide energy was limited the water or wind mills. Any other application of these technologies for the accomplishment of works was from little yield. Of the power plants, first and more important of the used ones by the man it was the firewood, due to the abundance of forests that proliferated throughout of the world. Other point sources were only used there where they were accessible, such as superficial filtrations of petroleum, coal or asphalts. In the average age the firewood began to be used to make charcoal with whose ores metals were obtained, and that later would come to be replaced by the mineral coal in the principles of the industrial revolution.