The PDF version of "Physics with Modern Physics" by Wolfson and Pasachoff is popular among students and instructors for several reasons:

Heat, internal energy, and the laws of thermodynamics.

Because the text does not shy away from calculus or complex reasoning, it can be intimidating for students who are taking their very first physics class. It assumes a level of mathematical maturity that some freshmen may still be developing.

The search term typically refers to the 11th chapter (or a specific digital version) of the classic textbook Physics for Scientists and Engineers by Richard Wolfson and Jay Pasachoff.

Before diving into complex derivations, the authors use everyday analogies to explain how the universe works.