Magnitude

AP Physics 1 EK 1.1.A.1 splits every quantity on this word: scalars are described by magnitude only, while vectors are described by both magnitude and direction. EK 1.1.A.2 makes it visual, modeling vectors as arrows whose lengths are proportional to their magnitude.

Notation. $\vec{F}$ is the vector, $\lvert \vec{F} \rvert$ or plain $F$ is its magnitude. The equation sheet uses both: it prints $\lvert \vec{F}_g \rvert = G m_1 m_2 / r^2$ with the bars, and $K = \frac{1}{2}mv^2$ without them, because $v$ there already means speed.

A magnitude cannot be negative. A velocity component of $-8$ m/s has a magnitude of 8 m/s; the minus sign was the direction, and taking the magnitude is what discards it. This is where marks go missing on vector subtraction, because the magnitude of a difference is not the difference of the magnitudes.

Two places the word does real work in the course. EK 1.4.A.1 says the choice of reference frame determines the direction and magnitude of what an observer measures. And the Topic 5.3 boundary statement says AP Physics 1 expects students to manipulate the magnitude of torque using vector conventions, while the direction of torque is beyond the scope of the course.