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". 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 principally problem solving: organizing this 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
Facts - definitions, properties such as 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