I like for general physics the following book to get started (if you have a healthy does of calculus and know basically nothing)
- University Physics (Young and Freedman)
It's also cool to watch MIT OCW Physics Lectures (Undergrad Freshman level is what I watched). Walter Lewin is one cool professor and researcher.
Some more specialized but really cool books that I found helpful (US gave Morin's at camp in 2012 and I believe Purcell/Morin's in 2013)
- Introduction to Classical Mechanics (David Morin)
- Electrictity and Magnetism Third Edition (E.M Purcell and David Morin)
- Thermal Physics (Schroeder)
In my opinion, these are the best books and I love Morin's problems.
Here are the books they gave at camp (US) in 2012:
- Introduction to Classical Mechanics (David Morin)
- Introduction to Electrodynamics (Griffith)
- Gravity: An Introduction to Einstein's General Relativity (Hartle) (Also an awesome book but I think not too helpful for IPhO. Read it anyways)
- Cosmology (Don't recall the author and can't find the book)
Disclaimer: I didn't actually make the US IPhO team in 2012 when I went to camp.
Disclaimer to Disclaimer: I was stupid in 2012 and 2013. I'm less so today.
