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What is energy? If asked, “Well, what exactly is energy, then?”, a lot of people pussyfoot around. You’ll find answers like: “energy is the ‘go’ of things” “energy is the capacity to do work” “energy is a mathematical quantity that is conserved in an isolated system”
Physicists like to the use energy unit called the joule (named after James Joule) because it makes their equations look simpler. There are about 4000 joules in a Calorie, 3600 in a Wh, 3.6 million in a kWh. The energy table below shows the approximate energies in various substances.
To understand energy and conservation of energy, we must first define some terms: work, kinetic energy (KE), and potential energy (PE). We’ll get to PE in the next Chapter.
The laws of thermodynamics deal with energy changes of macroscopic systems involving a large number of molecules rather than microscopic systems containing a few molecules.
Acceleration of the expansion of the universe is one of the most exciting and significant discoveries in physics, with implications that could revolutionize theories of quantum physics, gravitation, and cosmology.
The physics of energy involves a close interplay between underlying physical theory and applications. Thus, in 8.21 physical principles are developed in tandem with their applications to energy science. The subject material is loosely divided into three parts, covered sequentially throughout the semester.
The second law of thermodynamics asserts that processes occur in a certain direction and that the energy has quality as well as quantity. The first law places no restriction on the direction of a process, and satisfying the first law does not guarantee that the process will occur.
