Why learn about the relationship between work and energy?

In mechanics, physicists have learned to keep track of three fundamental quantities. Two of these quantities, linear momentum and angular momentum, tell us about how the motion of an object changes due to the forces that act on it. The most common way for us to keep track of momentum in introductory-level physics is using Newton’s Second Law. Because Newton’s Second Law is a vector problem, at this point in the course you should be comfortable drawing vector diagrams, picking coordinate systems, and breaking vectors up into components as part of setting up the necessary equations to solve a vector problem.

The third fundamental quantity that physicists have learned to keep track of is energy. Even from our day-to-day conversations, we know that meeting the demand for energy and increasing the energy efficiency of systems is critically important. What we will see during this course is that there are multiple forms of energy that a system may have. These forms of energy include, but are not limited to, kinetic energy and potential energy at the macroscopic level and the thermal energy of a system of particles at the microscopic level. Building off our understanding of forces, we will introduce ways to think about how forces act on a system to change its way the energy of the system is arranged. As forces act on a system, they do work which can transfer energy into or out of the system or convert it from one form of energy to another. We use the word “work” all the time, but in physics, it has a very specific definition. So to start our discussion of energy, we will begin by defining work.