What is Physics?

Introduction to Physics

Open most introductory physics textbooks and you will read that physics is the study of matter and light, and their interactions.  Indeed, physics offers understanding of the natural world that is awe-inspiring in its scope and precision  It explains the properties of atoms, how the moon, stars, and galaxies move, and how gravitation generated their obvious lumpiness, starting with a big bang uniform except for tiny quantum fluctuations (mandated by the uncertainty principle).   Physics allows you to notice significant things about the natural world and to explain them. The way, for example, H₂O molecules exist in gas, liquid, and solid forms, and why these forms of matter are so fundamental that water co-exists in all three forms at water's triple point, rather than simple turning into a 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 natural world are deemed to be "Laws of Nature" (sometimes called "theories" even though this word does not generally carry the requirement of experimental test).   In fact, physics underlies all other physical sciences: chemistry, biology, and even more specialized sciences like materials science, environmental science, earth science, and geology.  Following from these understandings, it enables the existence of entire fields of practical application called engineering : mechanical, electrical, civil, aeronautical, etc.

Physics as a way of thought

Historically, physics formed the core of the discipline called "Natural Philosophy". This 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 organizing this knowledge so that it can be applied to new situations, and being able to reach reliable conclusions about these situations.

Cognitive Structure of Physics

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

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

Concepts   -- e.g. Newton's Third Law

Concept clusters -e.g. That physical interactions result in forces on objects,

Representations - How to think about models (e.g. equations, graphs, pictures, words)

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

Hypotheses - consistently and logically developed guesses about how nature works

Laws of Nature - hypotheses with no experimental exceptions in their domains of validity

Experiments - careful observations of constructed situations that have the ability to falsify Laws