Physics - Introduction

Physics comes from the Greek phusis, meaning nature -- and true to its name, physics is the attempt to understand nature and natural phenomena in the most basic possible terms. Because it works with the smallest common set of ideas that can explain the widest range of happenings, physics is often called the most fundamental of the sciences: chemistry, biology, geology and even psychology all eventually lean on physical principles (see section 1.3).

Physicists use two complementary strategies to make sense of the world:

• Unification -- explaining many different-looking phenomena with a few concepts and laws. Newton's single law of universal gravitation, for instance, explains why an apple falls, why the Moon orbits the Earth, and why the planets orbit the Sun -- three very different-looking motions, one law.
• Reductionism -- explaining the macroscopic (bulk, everyday-scale) behaviour of a system in terms of its microscopic (molecular/atomic) constituents. Thermodynamics describes bulk properties like temperature and entropy; kinetic theory then explains those same bulk properties in terms of the motion of the individual molecules making up the gas. …