The world functions in this very concept of science. Energy can neither be created nor be destroyed, it can only be transformed from one form to another. This one fundamental law of physics which works on a spiritual level too.
My first brush with Energy Balance, popularly called the first law of thermodynamics was in class 9. It was a rather interesting concept to learn back then. Again, during my coursework in Engineering, we had a subject which purely dealt with concepts of thermodynamics including the energy balance. The most common application of first law of thermodynamics is the melting of an ice cube. When an ice cube is added to another liquid, the cube melts but the chillness is transferred to the liquid into to which it is dropped into. The energy here is transferred from the ice cube to the liquid into which it is destroyed.
My first practical exposure to an application of Energy balance was when I was working on correcting the air to fuel ratio of a steam boiler. Like every other engineering student, I was under the assumption that these laws weren’t going to be of any use and wouldn’t really matter once you are into a job. However, these very laws came back to haunt me during that project. I had to collaborate with a highly qualified person who was the energy head of that particular client site I was working in. He started off from this very law and ended up asking us to collate months worth data into a pattern which would explain the problem they were facing. I thanked my stars that I had paid enough attention to bring the data into a chart adhering to the law and come up with a solution. All the energy I spent on working on a solution was transferred into pages and pages of extensive notes. Talk about energy transfer! So much for assuming that these laws weren’t of any practical use!