155
 Unit B
The particulate nature of matter
INTRODUCTION
There is no better way to introduce this Unit than with a statement by Richard Feynman: âIf, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generation of creatures, what statement would contain the most information in the fewest words? I believe it is the atomic hypothesis that all things are made of atomsâlittle particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another. In that one sentence, you will see, there is an enormous amount of information about the world, if just a little imagination and thinking are applied.â
As we will see, the particle model of matter will help us understand the differences between solids, liquids and gases and how phase changes occur. For a gas we will be able to relate the microscopic concept of particles into macroscopic properties such as pressure, volume and temperature and see how each of these quantities is related to particle behaviour at the microscopic level. We will also see the effect of heating on a body and the ways in which heat can be transferred from one place to another. These are topics of great practical importance; life on earth is sustained because we receive radiation from the sun.
By studying thermodynamics we will discover an astonishing limitation to how much thermal energy can be converted into mechanical work and how this is related to a special law of Physics, the second law of thermodynamics and entropy. Finally, the particle model of matter, now applied mainly to electrons allows the study of electricity and the structure of electric circuits.