I'm a graduate student at Stanford, studying particle physics.

If you're a high school student interested in physics, you should register for the U.S. Physics Olympiad, the premier physics competition in the United States. The questions for the first round are solvable with only algebra-based mechanics, and are carefully crafted to stretch your intuition and teach you new things. It's how I first got interested in physics, and how lots of curious folks every year get into it!