An Introduction to Physics

Introduction to Physics

Physics is the study of space-time, matter, energy, motion, and and their interactions.  Its goal is accurate quantitative understanding, and its scope is the natural world.  It studies the origin of the universe and the structure and behavior of all its constituents, including the quantum world of atoms and the macroscopic world of gas, liquid, solid, plasma and other objects constructed from these.  Its scope is breathtaking, for example explaining the tiny quantum fluctuations (mandated by the uncertainty principle) and how these led through the action of gravitation to the large scale structure of the universe.   Physics allows you to notice significant things about the natural world and to explain them. For example, it explains not only the way H₂O molecules exist in gas, liquid, and solid forms, but also why these forms of matter are so fundamental that water co-exists in all three forms simultaneously at the Triple Point, rather than as a homogeneous soft paste. 

This understanding and insight is possible because physics is a science - a continuing process in which hypotheses that survive every well-done experimental test of their predictions against the actual behavior of the natural world are deemed to be "Laws of Nature". (Sometimes these Laws are called "theories," even though this word does not generally carry the requirement of an experimental test).   In fact, physics underlies all the other physical sciences: chemistry, biology, materials science, environmental science, planetary science, and geology.  These sciences, in turn, underlie entire fields of practical application called engineering : mechanical, electrical, civil, aeronautical, and biological among others.

Physics as a way of thought

Historically, physics formed the core of the discipline called "Natural Philosophy". "Philosophy" correctly emphasizes that physics is much more than a collection of facts, physical laws, and formulae - it is a powerful way of thinking about, and making sense of, the physical universe that we inhabit.  In order to understand the world-view provided by physics, and especially to apply its understanding and methodology to other areas, you must not only know the facts and some formulas, but you must also think like a physicist.  This involves principally problem solving: organizing your knowledge so that it can be applied to new situations, and being able to reach conclusions about these situations that are reliable and whose limitations and errors can be estimated quantitatively.

Cognitive Structure of Physics

To learn something well, you need to monitor your learning.  Part of this is understand the intellectual components of your subject and how they assemble into larger units and into the whole.  For example in Tennis you might learn various strokes (backhand, forehand, drop shot), assemble them into tactics (use the drop shot when the opponent is too far back), and ultimately combine all into a strategy (play long hard strokes that are safely in bounds to lengthen the game, tire your older opponent, and deny him opportunities to utilize his superior drop shots).  In an intellectual discipline like physics, there are also components in your mind that build into larger units.  Here is a way to think of the various levels:

Facts - definitions, properties such as the density of iron or air, or the value of the Gravitational Constant g

Concepts   -- fundamental ideas about nature e.g. Newton's Third Law

Procedures - e.g. how to define a system, or to draw a force diagram, or find the moment of inertia of an object about a given axis

Models - theoretical idealizations of the world (e.g. Circular Motion, Energy, Momentum)

Laws of Nature - hypotheses (logically developed theories about how nature works) that have survived extensive experimental tests within their domains of validity

Strategic Knowledge - Your ability to recognize which of your physics knowledge (particularly the laws and models) apply to a newly encountered problem in physics.

It will be important in constructing your own internal map of introductory physics to keep these distinctions in mind.  As your encounter new information, think about where it fits in this hierarchy.  Then, to optimize your learning, figure out how to do dedicated practice in the particular areas where you are weakest