To help orient the reader, the site uses coloured boxes (callouts): each box has an icon, a colour and a heading, so at a glance you understand what type of content you are reading — a principle to remember, a warning against a mistake, an optional deep-dive you can skip.
These are the callouts that recur throughout the text, with the colour in which you see them on the site.
- Principle (light blue): states a fundamental physical principle, for example the conservation of energy.
- Key formula (blue): highlights an important law or formula, such as Coulomb’s law or Newton’s laws.
- Exercise text (ochre yellow): the statement of a guided exercise; the Solution (green) usually follows immediately below, in a separate callout.
- Example (purple): presents a numerical or conceptual example directly within the discussion.
- Note (blue) and Info (cyan): brief clarifications, reminders and explanations.
- Hint and Deep dive (turquoise): practical advice or more advanced optional content, which can be skipped on a first read without losing the thread.
- Warning (orange; red for more serious errors): warns of a typical mistake, an ambiguity or a distinction that is often overlooked.
- Trivia and historical asides (in the form of a quote): anecdotes, history of science, unexpected applications.
Collapsible callouts and links
Many callouts can be expanded or collapsed by clicking on the heading (when it shows a small arrow). References to other topics are clickable links between atoms, and in the sidebar you will find the index for navigating between chapters.