High school students seeking online lectures on classical mechanics can find valuable resources from MIT, including various lecture sets available through a Google search. Notably, Walter Lewin's lectures, once part of MIT's OpenCourseWare, are now available on his personal YouTube channel, "Lectures by Walter Lewin." Lewin is highly regarded for his engaging teaching style and expertise in physics. His channel features playlists for different courses, making it a great resource for students preparing for competitions like the IPhO. Utilizing these lectures can significantly enhance understanding and appreciation of classical mechanics.