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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.
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