Reference Library

Every equation's own symbol table, opened from its popup, is the authoritative reference for that formula's notation. A handful of symbols are deliberately reused across modules with a consistent meaning: r for a radial distance, θ for an angle from a reference direction, ω for angular frequency.

Sign conventions are a recurring source of error, not because the underlying physics is hard but because equally valid choices differ from one context to the next — current direction, mirror and lens distances, and work in the first law of thermodynamics all vary by convention. When a result comes out with an unexpected sign, check the convention in use before assuming an error in the physics.

An arrow over a symbol denotes a vector, carrying both magnitude and direction; a hat denotes a unit vector, of magnitude one, giving direction alone. A vector's magnitude is written without the arrow, or between vertical bars — |A⃗| and A mean the same thing. This reference follows that convention throughout.