The purpose of an introductory-level physics class is to introduce you to the handful of physical concepts that physicists have learned over the years to keep track of and measure because they are so fundamental to our understanding of the world around us.  Energy was one of those concepts.  When we introduced energy, we talked about how energy is so fundamental, it is actually difficult to define in words.  As a result we tend to hide our verbal shortcomings behind an equation.  In the end, what we have learned to do with energy is how to recognize it and how to keep track of it and how it changes for a system.

Momentum is another of those fundamental concepts that physicists cherish.  Momentum is also very difficult to define in words so we will often use an equation to give its definition.  And just like energy, the goal over the next few modules will be to learn to keep track of momentum and how it changes for an object or a system of objects.

As we will soon see, we have actually been working with momentum almost since the beginning of the course.  Though we haven’t made the connection explicit before now, Newton’s laws are actually about momentum.  Thinking about how force act on an object to change its motion is equivalent to thinking about how forces act on an object to change its momentum.  Introducing momentum will let us expand the approaches we have for using Newton’s second law and a vector framework for solving for how an object or a system evolved over time.