Integrated SequencePhysics Chemistry Organic Biology

Web Resources

HyperPhysics - Fundamental Forces

Wikipedia - Fundamental Interaction
Nice survey article of the 'Fundamental Forces' from a modern perspective.

HyperPhysics - The Electromagnetic Force

PY106 Notes - Electric charge and Coulomb's law
Introduction to electrostatics with a conversational, easy-to-understand way of expressing concepts. Includes a comparison of the electric and gravitational forces.

HyperPhysics - Exchange Forces
Advanced topic.

HyperPhysics - Spontaneous Symmetry Breaking
Advanced topic.

HyperPhysics - Feynman Diagrams
Advanced topic.

  click if a link is broken

Special points of emphasis


Newton's Laws


Gravitation will be an important context to apply the concepts you are learning in Newton's Laws. There is a central conceptual intersection between Kinematics, Newton's Laws, and Gravity.

In some contexts, gravitational force leads to constant acceleration kinematics. In other contexts, the acceleration of an object may change.

In cases where the gravitational field changes very little over the distances involved, gravitational force can be treated as constant, so the kinematics that result are constant acceleration. In such a constant field environment, the field lines would not significantly diverge over a small distance if you were to draw them on paper. In other words, parallel field lines signify a uniform field.

Try to picture the earth from space, and you would see the gravitational field lines spreading out into space. But if you think of the field within the room you are in, the field lines would appear to be parallel lines from the ceiling to the floor. This approximation of the gravitational field as constant allows us to treat the weight of an object on the surface of the earth as a constant value, although weight slightly decreases the further one gets from the center of the Earth (we weigh a bit less on top of a mountain than we did in the valley).

In summary, the space at or near the surface of the Earth is an area in which gravitational force is for most practical purposes a constant force, i.e. constant acceleration, environment. For problem solving, remember that the model for motion within this environment is projectile motion or free-fall. If differences in position under consideration are large compared to the distance between the bodies, then the force will be noticeably diminished with increasing separation.


Newton's Laws



Electromagnetic interactions are another important context for the application of In the context of Newton's Laws, it is important to be thinking about the fundamental forces, which are the only types of force interactions observed. Of the four fundamental forces: 1) gravitational, 2) electromagnetic (electrostatic & magnetic), 3) strong nuclear and 4) weak nuclear, at this stage in the course, we are especially concerned with the gravitational force and the electrostatic force. The comparison and contrast of these two forces is a major theme. As the course progresses, we will also occasionally mention the flip-side of electrostatic force in these discussions, the magnetic force. At this stage, though, when we mention magnetism, this is mainly to create an expectation, or a sense, of its importance, not to make you panic. We will have much to say about magnetism much later in the course.

As with gravitation, an electrostatic system might produce an environment where the force on a particle is the same everywhere, or, conversely, the force might change at different points within the system. A commonly discussed constant force environment for electrostatic force exists in the space between the plates of a parallel plate capacitor. This environment is a frequent MCAT motif.

As a side note, keep in mind that there is an interesting constant field environment for the magnetic force, which exists in the space within an inductor (or solenoid). Behavior within this type of environment is another frequent MCAT motif, so keep it in the back of your mind that inductors are going to be something important to deal with.

Between the plates of the capacitor, charged particles move similarly to projectile motion. Within an inductor (if energy dissipation is ignored or insignificant) charged particles move with uniform circular motion if the particle initially entered the field with a velocity perpendicular to the field lines.

All of the sudden I am bringing magnetism into this discussion. What I am saying is for you to start looking for these constant field systems in your problem solving and practice MCATs and start thinking about it: gravity near the earth's surface, the electric field between parallel plates, the magnetic field within a current carrying coil.

This is something we will often do in these discussions, preview later material in the context of a current concept. Here we are talking about Newton's Laws, which govern basic force interaction. An important theme are the fundamental forces, and so I am taking an opportunity to point out a major set of the simple model systems used for teaching and problem solving, i.e. the constant field environments for gravitation, electrostatics, and magnetism.

Sometimes in these discussions, it is not important that you completely understand at first, but that you clue in and stake a claim to begin a theme of development. I have taught many students so I know what will make most of you uncomfortable. My job at this stage, with some of these ideas, is actually to produce discomfort sometimes. Please understand that I am signaling an expectation of knowing, not the need to panic. As we return again and again to the most important concepts, the discomfort will give an impulse to your learning and it will resolve to your satisfaction. Each repetition reconfirms the importance and builds familiarity into knowledge.

In this discussion, for example, I am saying 'Watch out for solenoids', way back here in Newton's Laws. Later, when you see one in a modern physics apparatus, maybe cathode ray moving into the region of current carrying coil in an MCAT passage, you will say, 'There one is again! There is a constant magnetic field in that thing!'

Newton's Laws


Atomic Theory

The Chemical Bond

Intermolecular Forces

As you take a moment to gain an overview of the fundamental forces, a preview of gravitation and electromagnetism at this stage of this MCAT Course, within this section of basic mechanics there is something else I want you to keep in mind. This is important so grip down and pay attention. The point I want to make is that the chemical properties of substances are in large part determined by electric forces between nuclei and electrons within atoms, between atoms in bonding, and between molecules.

In other words, the basic Physics in Mechanics and Electricity are directly relevant to understanding Chemistry. While not forgetting that quantum electrodynamics has greatly improved our understanding, much insight can still be gained by viewing the atom as a simple, classical electrical system (while keeping quantum mechanics in the back of the mind). In other words, as we move through Electricity in a few modules, keep in mind that you are gathering concepts to help you understand Chemistry.

Electric force is a carinal factor in the behavior both within atoms and between atoms. Electricity binds electrons in orbit to the nuclei of a single atom, and electricity binds atoms together in chemical bonds. Panning back the view further, electricity binds molecules together through intermolecular force.

To reprise, looking at the atom itself, electricity is found underlying the atom's ionization energy, for example (electric force is the glue holding the nuclei and electrons together). Looking at phenomena derived between atoms, electricity underlies the dissociation energy of the covalent bonds (electricity holds the atoms together in covalent bonds). Looking at phenomena between molecules, extending the view back, electric force holds the molecules together in a solid or liquid, for example.

Electricity is the primary force determining chemical behavior. Put that in your head! Get into the habit of trying to see every chemical event in the light of basic classical electrodynamics. Don't be afraid to help your basic understanding with the classical model and then keep in mind where the quantum model corrects the picture.

The WikiPremed MCAT Course is a free comprehensive course in the undergraduate level general sciences. Undergraduate level physics, chemistry, organic chemistry and biology are presented by this course as a unified whole within a spiraling curriculum.

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