Pure physics begins not with equations, but with stripping reality down to its essentials. When Galileo considered falling objects, he ignored air resistance, surface texture, and even color — focusing only on mass, distance, and time. This idealization is the first cognitive step: isolating a few variables and assuming all others are negligible or absent. The key question is: What can I ignore without losing predictive power?
You must be cautious. Many "free PDF" sites host outdated or incorrectly scanned books. Here are legitimate sources:
Before any math, define the system.