Before tackling motion and forces, it is worth getting comfortable with the physicist’s basic tools: physical quantities, units of measurement, order-of-magnitude estimates, vectors and the first concepts of force and equilibrium. This introductory chapter serves as a review of the first two years of secondary school: many topics will return with more formalism in later chapters. It closes with fluid statics (pressure, Stevin’s law, Pascal, Archimedes) and a taste of fluid dynamics.
From Aristotle to Galileo: physics as "natural philosophy"
Physics starts from questions — what is it? what is it made of? how does it work? why? In antiquity these questions were part of natural philosophy: from Aristotle onwards, for centuries the prevailing method was “think and deduce”. It was Galileo, at the start of the seventeenth century, who changed the rules of the game: answers about nature must be objective (all observers must agree, the result must not depend on who asks the question). Achieving this requires measurement and mathematics. As Galileo wrote, the book of nature “is written in the language of mathematics, and its characters are triangles, circles, and other geometric figures” (Il Saggiatore, 1623). Every statement is a measurement, every law is an equation.
Physics as a treasure hunt
A physics problem resembles a treasure hunt: there is a starting point, the treasure, and territory to explore in between. Six mental tools guide every exercise in the book:
- Dock — read the text carefully (data, units, implicit assumptions: more than half of all errors originate here).
- Equipment — list the formulae, laws and concepts that might be useful.
- The treasure — precisely identify the quantity to be found.
- Build new tools — introduce a reference frame, an auxiliary variable, a diagram.
- Specialise (analysis) — examine a small piece of the problem, a particular case.
- Generalise (synthesis) — ask whether the result fits into a bigger pattern.
And two voices always accompany you: the inner enemy (the devil’s advocate, “but are you sure?”) and the naive child (who asks apparently stupid questions, but often exposes mistaken assumptions).
Sections
- Physical quantities and units of measurement
- Fermi estimates
- Trigonometry and indirect measurements
- Vectors: operations and components
- Forces as vectors
- Static equilibrium
- Fluid statics: pressure and fundamental laws
- Archimedes’ principle
- An introduction to fluid dynamics