A particularly simple system for understanding thermal behavior is the ideal gas, comprising widely spaced, non-interacting molecules. Theoretical analysis of the ideal gas using Newtonian mechanics reveals that temperature is a measure of molecular kinetic energy. Consequently, temperature is also a measure of the typical molecular speed. Real gases under ordinary conditions obey the ideal-gas law with remarkable accuracy, and the ideal-gas law encompasses not only idealized point-like molecules, but also real, complex molecules that can rotate and vibrate.