Introduction to Physics

Why does a ball thrown upward slow down, stop, and fall back? Why does a passenger lurch forward when a train brakes? Physics is the study of questions like these — of matter, energy, motion, and the forces that connect them. It gives us a precise way to describe the world, test our ideas against evidence, and predict what will happen next.

How Physics Works

Physics is built on a simple cycle. We observe a phenomenon, propose a model to explain it, express that model in the language of mathematics, and then check its predictions against experiment. A model that survives repeated testing becomes a law; one that fails is revised or discarded.

Mathematics is not decoration in this process — it is what makes the predictions exact. Saying “the ball falls faster and faster” is an observation; writing down how much faster, at what rate, is physics.

Where We Begin

We start with mechanics, the study of how bodies move and why. Every later branch of physics borrows its vocabulary — position, velocity, force, energy — so it is the natural foundation for everything that follows.

Mechanics itself begins with the language we need to describe motion: quantities that have a size and a direction. That language is the language of vectors.