Have you got a nerdy 18-year-old nephew who spends all day in front of his computer, and is planning to go to college next year to study science? If so, I just solved your Christmas present problem. And it won't cost you a penny.
Well, actually, it's Paul Perry (ex-secondhand book dealer and now an analog electronic designer) who's solved the problem for you. Because Paul has written to tell me about a university-level Physics text book which he thoroughly recommends and which is available free.
You can find the text online (naturally) at the Motion Mountain. It turns out to have been written by Christoph Schiller, who got his first degree in Stuttgart, his PhD in Brussels, wrote the book mostly in Holland, and lives in Italy.
This book has, it seems, been online since 1997, is in its 18th revision, and 226,438 people have taken a look at it.