Population is increasingly important as both a scientific and a political subject. The world is getting more crowded. Providing students with the tools to understand population numbers is not only important for their basic understanding of their world, but it is also essential for their future navigation of social and political subjects ranging from energy use and the environment to globalization and the economy. How many people live in your city? Your state? Your country? Your world? How many people live in the United States versus China? This exercise helps students explore the magnitudes of populations and build familiarity with the scales of city, country, and world populations. A related exercise explores the connection between population and energy consumption by comparing the populations of various countries and their corresponding use of oil. This free selection includes the Table of Contents, Introduction, and Index. As a special bonus, the chapter entitled, That’s Hot! The Effect of Size on Rate of Heat Loss is also included.