Home Energy Audit

Authors

Pod(s)

Home Life, Energy

Module(s)

Home Energy

Abstract

In the 1800's, scientists found, empirically, that rules exist that determine how energy can be transferred. The first of these rules is called the First Law of Thermodynamics. This law is usually stated as, "Energy can neither be created nor destroyed; it can only be transferred from one form to another." This often leads to the re-titling of this law as the Conservation of Energy Principle since it says that energy must be conserved. This statement of the First Law does not say anything about how energy can be transferred, though. It turns out that there are only two ways. This was discovered in 1850 by the English scientist James Joule, who found that heat and work are equivalent methods for changing the energy of an object. In his experimental work, Joule was able to show that he could increase the thermal energy of a pot of water by either placing it over a flame (adding heat), or by stirring it with a paddle (doing work). For this and other important work in this area, the SI unit of energy is called a joule (1 J = 1 kg m 2 /sec2). Using this, we can re-write the First Law mathematically as ∆E = W + Q where ∆E is the change in the energy of an object, W is the work done on the object, and Q is the heat added to an object. In laymen's terms, this means that the only way to change the energy of an object is to exchange either work or heat with it.