Energy has always been the key to all the human goals and his dreams for a better world. The caveman began the civilization after he used the energy of fire to get light and heat, and his body energy to survive and eat.

Using the horse, man could move faster than using his own legs. With this animal, they shared the production of energy, water and wind. This was one of the first times, man tried to improve his work limited by his muscles. In the following centuries coal, oil and electricity were used to make his life easier. The mechanics slaves (gas particles and electrons) moved the machines faster and without fatigue. This was the beginning of an era where man controls the process instead of making muscular and rutinary hardwork. Now a day, the moon was reached thanks to the chemical energy and the conquest of planets is on the way.

We live in a sea of energy. Everywhere we look, nature is working producing energy in such a way that we just exploit a tiny fraction of it. Rivers are giving us 2% of our needs, but could give us as much as 80%, winds could give twice as rivers, the tide could satisfy 50% of the demand. The dynamo that affects everything on Earth is the Sun; if all the fuels of the world could burn together to equal what we receive from the Sun, they would finish in four days.

Galileo Galilei was the first man to really study the energy. In 1583, at 19 years old, he saw a lamp pending from a large chain. The lamp went from one side to the other in the same time. Without a clock in that time, he counted his pulse between each oscillation. Observing this phenomenon he afirmed that "the period for the back-and-forth oscillation of a pendulum of a given length remains the same, no matter how large its arc or amplitude."

Galileo also made important experiments to prove that everything falls at the same speed in a space without air. This incited others to study Mechanics, the science that opened the mind to the world of energy. The mathematicians like Renato Descartes, Isaac Newton and Gottfried Wilhelm von Leibniz made the concept of force.

Leibniz saw that a big weight in a body causes more damage than a little weight when falling to the Earth, no matter if the time is the same. There was a way to measure a force. It is obvious that the impact depends upon weight and height (everybody knows that a block makes less damage from 1 feet than from 100 feet); but suppose that we are interested in a ball going up or straight horizontally, ¿how does the weight affect the measure? Leibniz concluded that height was not really important but the speed of the object. He named the impact vis viva or living force. The formula used by Leibniz to measure the vis viva is the same used today to measure the kinetic energy.

At the same time Leibniz was studying in Germany, Christian Huygens, Dutch mathematician, stated that when two or more objects are impacted by themselves, the vis viva of all the objects is the same before than after the impact. This observation at the XVII century is the base for the law of conservation of energy, stated in 1850.

In 1803, L. N. M. Carnot concluded that a weight in the top of a place has energy just because it can fall down and generate kinetic energy; Carnot called that energy latent vis viva, later named potential energy. Four years later, in 1807, the term energy was used instead of vis viva

Also the terms work and power are used. Work is an aplicated force, this is, a force aplicated through a certain distance. The speed at which work is made, is called power.