“It is important to realize that in physics today, we have no knowledge what energy is. We do not have a picture that energy comes in little blobs of a definite amount. It is not that way.”

“Energy is a numerical quantity, which does not change when something happens….”

The above quotes come from Richard Feynmann, a 20th century physicist who is thought to have some of the greatest insights into the physical world. He's being a bit flippant about our knowledge of energy, but he's not wrong. We don't know what energy is. We know that energy is a conserved quantity. That is, you can track the energy of a system and see that it changes forms, but it is not created or destroyed. In this set of notes, you will read a brief bit about the history of different energy ideas, about the different forms of energy, and the first law of thermodynamics (conservation of energy).

The greek philosopher Aristotle is often attributed with the first discussion of energy, but not in its modern form. Aristotle, like many philosophers of his time, were concerned with connecting the physical world to the human experience. Aristotle's and others' of the time “scientific” arguments were not grounded in science as we know it now, but more natural philosophy. That is, a well-spoke argument could go a long way even if it had little scientific evidence to back it up. Aristotle's concept of energy (energeia) was more like the idea of work. But it applied not only to physical systems, but to other natural systems as well, including human emotion. Two examples of energy applied to human emotion in Aristotle's work are pleasure and happiness. Pleasure is the energy of the human body while happiness is the energy of the human being human.

In the 17th century, Isaac Newton and Gottfried Leibniz provided our first understanding of the modern concept of energy. They built off of the great work of mathematicians like Archimedes and physicists like