Most of this notebook is derivation: long chains of steps written out in full so the reasoning stays recoverable. This shelf is the opposite exercise. Each entry is a short question about the physical world — statable in a few sentences, answerable rightly or wrongly before any machinery is switched on. Each question stands on its own page, with the solution folded beneath it.
The intended use is strict. Read the question, commit to an answer — say it out loud if you have to — and only then open the fold. A question you answer before checking teaches something; a question you read through teaches almost nothing.
The genre is old. The Peripatetic Problemata collected hundreds of short physical questions — why does…, whether… — and the format has survived because it exercises something derivations do not: saying what happens before calculating why. Where the machinery is genuinely needed, each solution links back down into the notebook where it lives.
Questions of this kind are folklore. Most have been asked in one form or another for a century, some for much longer; the statements and solutions here are my own wording. The collection opened with relativity; mechanics has now joined it, quantum questions will follow, and the numbering simply continues.
Relativity
Ten questions, roughly in order of increasing depth. The first five need nothing beyond special relativity; the middle three run on the equivalence principle; the last two need a black hole and an expanding universe.
Mechanics
Four questions to open the shelf: two spent on mechanical similarity, one on the kinematics of rolling, and one on the way dissipation makes an oscillator forget.