Last semester you learned (I hope) that when one pushes on something, it accelerates, and that when all the pushes balance (or vanish) the object doesn't accelerate. This is a simple view of Newton's Laws, and most of the semester was spent understanding them and learning their consequences.
One thing that we discovered was that the notion of what it is that does the pushing gets fuzzy at the microscopic scale. We saw some of this at the macroscopic scale. One of our favorite forces was gravity. However, gravity exerts a force on an object over here due to another massive object over there. This is difficult to fully understand - how does an object over there do anything to one over here? They are not in contact. There are no ropes or pulleys or springs connecting them. Yet they accelerate in a way that makes it clear that there is a force between them.
If we look inside the ropes and pulleys and springs, the same problem exists. All of these objects are made up of molecules which are made of atoms which are made of electrons and nuclei which are made of protons and neutrons which are made of quarks, and something is holding each level of ``elementary'' particle together to form the ``elementary'' particle of the level above it. We labelled all of these forces, although in each case there is no direct contact (so to speak) between the massive objects interacting by means of these forces. The strong nuclear, weak nuclear, electromagnetic and gravitational forces are thought to be the only forces that glue all of the particular (massive) parts together into the wholes.
Although this was very useful, it doesn't solve our philosophical difficulties: How is it possible for an object (particle) over there to act upon one over here? Indeed, what is the nature of the space in between that we blithely cover with coordinates and arrange into a sequence of time-labelled events? Finally, how can we understand the greatest mystery of all. The interactions we observe and name have a geometric structure, and the equations of motion for systems of particles connected via these interactions somehow blend geometry in our coordinatized space and calculus.
I wish that I could tell you what the answers to these questions are. Unfortunately, they don't have an answer that can just be told. The only way to begin to appreciate the answers to these questions is to study one of these interactions in complete detail, hoping that as our mechanical understanding of the interaction increases, so will our philosophical insight into its true nature.
But which interaction should we choose to look at? There is really no
choice - it is obvious. Gravity is too simple (or too complex); you
already know nearly all there is to know about gravity until you learn
differential geometry, general relativity, and quantum field theory.
Nuclear forces are too subtle and too hard to get a handle on. They
have a finite range (on the order of 
meters) and we just
can't see what they are doing with anything less than an accelerator
laboratory (and again, a pretty detailed understanding of quantum
theory).
However, the electromagnetic interaction is not only visible, it is the basis for sight itself and all human experience. Electromagnetic forces are the only forces of sufficient strength and range to be simply studiable in a laboratory setting at both the macroscopic level (the one that makes lightning, electric lights, electric motors) and the microscopic level (the one that holds atoms and molecules together, produces or absorbs light, and mediates chemical processes including the rather complicated ones that give rise to life). The electromagnetic force is not only ubiquitous to human experience, it is human experience!
For that reason, we will pursue the electromagnetic interaction this semester. We will stalk it wherever it lurks, beginning with its simplest manifestations, which already determine the basic geometric forms that ultimately lead to all that complexity. We will follow it as it leaps from charge to charge (without really understanding the nature of the leap itself, but understanding well its geometric form), twists and turns about accelerating charges, and acts as an invisible messenger carrying momentum and energy about. When we are done, with luck, you will have a far richer understanding of nearly everything.
The electromagnetic interaction is one of the most mathematically beautiful things in nature, and its discovery and taming is a profound story of the triumph of the human spirit. Electricity is a promethean gift; it quite literally is the primary thing that separates the human race from savagery - imagine even for a moment a world without electricity and you imagine a world of poverty and misery the likes of which existed more than 100 years ago when children died young, when life expectancy was short, when industry (such as it was) was driven by steam or water or beasts or the labor of human hands and backs, and when nights were dark and smoky affairs with the danger of fire a constant companion.
With electricity (and a solid grasp of physics) we have refrigeration, electric light, heat, and air conditioning, electric motors to turn the wheels of industry, electronically reproduced music, television and movies (for better or worse), exotica such as lasers, and last but not least a whole revolution in information processing that promises to remake the entire world yet again. We have become so wealthy, with the instant, silent, clean servant of electricity available to feed us, to care for us, to monitor and uplift our lives, that we have forgotten what it is like to be poor. Only by visiting a third world country, which is almost by definition one where electricity is scarce and expensive, can one still see life as it was before it became commonplace.
Few subjects in physics are more of a key to other studies in other areas and disciplines that that of electromagnetism. It is virtually impossible to perform science or develop technology without a detailed working knowledge of electromagnetic fields and phenomena. The human body relies tremendously on electromagnetism on both the large and the small scale. Optics, light, the manipulation of information in computers - all is built upon electromagnetism. Whether or not you wish to be a scientist or engineer, if you wish to be a thoughtful and informed member of our society, then you should work hard to master this subject; it is a useful and fitting accomplishment for any civilized person. ======= »»»> 1.5