These two volumes cover the classical topics typically taught in undergraduate physics courses and beyond. However, they also possess unique characteristics. In these volumes, we teach classical physics using a very different language from traditional books, influenced by the language of modern physics, in a move to encourage a positive approach towards the latter. The concept of energy serves as the unifying aspect in physics, spanning from mechanics to thermodynamics, electromagnetism and modern physics. The organisation of the material into chapters also reflects the distinct approach taken in these volumes. We present physics in a unified manner without separating topics such as mechanics, kinematics, thermodynamics, electricity, and magnetism. Instead, physics is revealed gradually, emphasizing a holistic approach to science. Despite this peculiarity, we have maintained the conventional separation between Physics I and II to assist potential teachers in adopting these books steadily and securely.These innovative volumes present valuable new perspectives. Although their approach is bold, they will certainly prompt interesting reflections on traditional teachings. This first volume contains chapters on temperature, optics, waves, motion, special relativity, Newton's laws, forces and work, inertial and non-inertial frames, momentum, the physics of gases, and thermodynamics, among other topics.