Electromagnetic

Physicists in the twentieth century came to recognize four different fundamental forces in nature: (1) gravitational force, (2) electromagnetic force (we will see that electric and magnetic forces are intimately related), (3) strong nuclear force, and (4) weak nuclear force. The last two forces operate at the level of the nucleus of an atom. Recent theory has combined the electromagnetic and weak nuclear forces so they are now considered to have a common origin known as the electroweak force.

Many of the forces we have dealt with so far, such as elastic forces, normal forces perpendicular to surfaces, friction forces parallel to surfaces, tension forces along strings and other contact forces (pushes and pulls), are now considered to result from electric forces acting at the atomic level. gravitational forces, on the other hand, is a separate force. Gravity plays a role in nature by allowing planets to exist, but life on that planet is due to electricity!

The laws of electricity and magnetism play a central role in the operation of such devices as smartphones, televisions, electric motors, computers, high-energy accelerators, and other electronic devices. But the electromagnetic force plays an even deeper role in our lives. According to atomic theory, electromagnetic forces between atoms and molecules hold them together to form liquids and solids, and electromagnetic forces are also involved in the metabolic processes that occur within our bodies.

Our understanding of the gravitational force developed according to a conceptual structure that we built: we learned that the force exists between objects with mass. We then developed a mathematical law, Newton's law of universal gravitation, to describe the magnitude of the force. We then introduced the notion of a gravitational field. From there we discussed gravitational potential energy in a system of two or more massive objects. We will follow a similar conceptual development in our study of the electric force. We will learn that the force exists between objects with electric charge. We will develop a mathematical law, Coulomb's law, to describe the magnitude of the force. We will introduce the notion of an electric field, and we will discuss electric potential energy in a system of two or more charged objects. As we continue to study the electric force, we will find that we have much more control over this force than we do over gravity. Sources of gravity are restricted to one shape: the spherical shape of planets and stars (with the exception of small asteroids and moons that might deviate slightly from spheres). On the other hand, we can formulate various shapes for electrical situations: spheres, plates, wires, and the like! Objects moving in gravitational fields are huge and massive; we can't control their motion. Objects moving in electric fields can be as small as electrons; we can easily change their motion! We have no control over gravity; it's always there. But we can turn electricity on and off! We can't adjust the strength of the gravitational field of the Earth. But we can easily turn a dial to change the strength of an electric field! Gravity is everywhere, inside and outside of everything. But some materials conduct electricity and others don't! And we can create electric field-free regions of space quite easily! This type of control that we have over electricity makes it the basis of our technological society.