Lectures on Physics has been derived from Benjamin Crowell's Light and Matter series of free introductory textbooks on physics. See the editorial for more information....

Summary - Introduction to Physics

Physics is the use of the scientific method to study the behavior of light and matter. The scientific method requires a cycle of theory and experiment, theories with both predictive and explanatory value, and reproducible experiments.

The metric system is a simple, consistent framework for measurement built out of the meter, the kilogram, and the second plus a set of prefixes denoting powers of ten. The most systematic method for doing conversions is shown in the following example:

Mass is a measure of the amount of a substance. Mass can be defined gravitationally, by comparing an object to a standard mass on a double-pan balance, or in terms of inertia, by comparing the effect of a force on an object to the effect of the same force on a standard mass. The two definitions are found experimentally to be proportional to each other to a high degree of precision, so we usually refer simply to "mass," without bothering to specify which type.

A force is that which can change the motion of an object. The metric unit of force is the Newton, defined as the force required to accelerate a standard 1-kg mass from rest to a speed of 1 m/s in 1 s.

Scientific notation means, for example, writing 3.2 105 rather than 320000.

Writing numbers with the correct number of significant figures correctly communicates how accurate they are. As a rule of thumb, the final result of a calculation is no more accurate than, and should have no more significant figures than, the least accurate piece of data.

Exploring Further

Microbe Hunters, Paul de Kruif. The dramatic life-and-death stories in this book are entertaining, but along the way de Kruif also presents an excellent, warts-and-all picture of how real science and real scientists really work - an excellent anecdote to the sanitized picture of the scientific method often presented in textbooks. Some of the descriptions of field work in Africa are marred by racism.

Voodoo Science: The Road from Foolishness to Fraud, Robert L. Park. Park has some penetrating psychological insights into the fundamental problems that Homo sapiens (scientists included) often have with the unwelcome truths that science tosses in our laps. Until I read this book, I hadn't realized, for example, how common it is to find pockets of bogus science in such otherwise respectable institutions as NASA.

Last Update: 2009-06-21