For preparation for the F=MA contest and advancement to USAPhO, it's essential to choose the right textbooks. While Khan Academy offers a solid foundation, many find it insufficient for deeper understanding. HRK Physics may lack engaging problems, leading some to seek alternatives. David Morin's "Introduction to Classical Mechanics" is noted for its challenging problems and depth, particularly in special relativity, making it suitable for those with a strong background. In contrast, Taylor's "Classical Mechanics" is recommended as a more approachable introductory text, covering fundamental concepts clearly and effectively. It’s suggested to start with Taylor before progressing to Morin. For high school students, Morin's other book aimed at AP students provides a more accessible entry point while still being calculus-based. Additionally, Walter Lewin's physics lectures on YouTube are highly recommended for their engaging content.