Physics

Where to actually learn physics, from mechanics up.

Lecture notes

David Tong — Lecture Notes (Website) — a Cambridge theoretical physicist's full set of free, exceptionally clear course notes, from first-year mechanics to string theory.

• Dynamics and Relativity (Article) — first-year Newtonian mechanics and special relativity, ~160 pages with problem sheets.
• Quantum Mechanics (Article) — the standard introductory QM course.
• General Relativity (Article) — gravity as curved spacetime, worked through carefully.

Articles

• What happens when a raindrop hits a puddle (Article) — Nate Barlow, a mathematician at RIT, on why puddle ripples spread out into rings: in shallow water surface tension beats gravity, so the waves are dispersive and each wavelength travels at its own speed. In deep water gravity takes over and the effect vanishes, so the number and spacing of the rings reads out the puddle’s depth.

Interactives

• Making Music with Math (Interactive) — Aatish Bhatia solves the wave equation for a vibrating string, then synthesizes it plucked, struck and bowed, with sliders for the first six normal modes and audio you can play. The Fourier coefficients explain the timbre: a struck string’s harmonics fall off as 1/n against a plucked string’s 1/n², which is why it sounds noticeably harsher.

Videos

• Is Perfect Prediction Possible? (Video) — Henry Reich of minutephysics responds to Veritasium’s video on Newcomb’s paradox in 14 minutes: one box or two, when a predictor has already guessed which you’ll take? He works through causal calculus and intervention, then turns to quantum mechanics and whether a perfect predictor can exist.