Physics in Everyday Life

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Contents

The Foundations of Physics

1 Studying the Material World

2 Forces, Energy and Motion

3 Sound

4 Molecules and Matter

5 Light

6 Magnetism

7 Electricity

8 Electromagnetism

9 Atoms and Elements

10 Using the Elements

The World within the Atom

11 Studying the Nucleus

12 The Quantum World

13 Elementary Particles

14 Fundamental Forces

15 Radiation and Radioactivity

16 Nuclear Fission and Fusion

Studying the Material World

The ancient view of matter...Greek science...Islamic

astronomy, physics and alchemy...Medieval science...

Dalton and modern atomism...Physics and chemistry in

the 19th century..Modern physics and chemistry...

PERSPECTIVE...Greek atomism...Chinese science...

What do physicists and chemists do?

The earliest efforts to understand the nature of the physical world

around us began several thousand years ago. By the time of the

ancient Greeks, over 2,000 years ago, these attempts at explanation

had become both complex and sophisticated. They were characterized

by the desire to find a single explanation which could be applied to all

happenings in the physical world. For example, the description of the

world that received most support supposed the existence of four

primary chemical elements - earth, water, air and fire. This list may

look odd to us but we should see it as something like the modern

division of substances into solids, liquids and gases (-> pages 25-34).

These four elements were considered to have particular places where

they were naturally at rest. The earth, preferentially accumulated at,

or below, the Earth's surface; the water came next, lying on top of the

Earth's surface; air formed a layer of atmosphere above the surface;

and, finally, a layer of fire surrounded the atmosphere. This layering

of the elements was invoked to explain how things moved on Earth. A

stone thrown into the air fell back to the Earth's surface because that

was its natural resting-place; flames leapt upwards in order to reach

their natural home at the top of the atmosphere, and so on.

Greek philosophers set the scene for later studies of the material

world by distinguishing between different types of theories of

matter. The Greeks pointed out that two explanations are feasible.

The first supposes that matter is continuous; so that it is always

possible to chop up a lump of material into smaller and smaller pieces.

The other theory supposes that matter consists of many small

indivisible particles clumped together; so that chopping up a lump of

matter must stop once it has reached the size of these particles.

The four humors

The chemical elements could combine to create new substances - in

particular, they formed the "humors". Each individual human being

contained a mixture of four humors, made up from the four elements,

and the balance of these humors determined the individual's

nature. This theory is still invoked today when we say someone is in a

"good humor". Indeed, some of the Greek technical terms are still

used: "melancholy" is simply the term for "black bile", one of the

four humors. So the chemical elements of the ancient Greeks were

involved in determining motion, a fundamental part of physics, and

in determining human characteristics, an area now referred to as

physiology and biochemistry. The Classical world did not distinguish

between physics and chemistry, but saw all of what we would now call

"science" as an integrated whole, known as natural philosophy; by the

end of the period, however, a distinction between the two areas of

study was beginning to emerge as practical studies in alchemy

developed that field into a separate area of knowledge.