Distance

AP Physics 1 EK 1.1.A.3 files distance with speed on the scalar side, against position, displacement, velocity and acceleration on the vector side. Distance is therefore never negative and never carries a direction.

The two senses are worth separating, because the exam mixes them.

• Path length. How far the object actually went, adding up every segment of the route. Run a lap and you cover the full lap; the displacement is zero. The full comparison is in distance vs displacement.
• Separation. A gap between two points, with no journey involved. This is the sense on the equation sheet, whose symbol list reads $d$ = distance and $r$ = radius or distance. In $W = F_\parallel d = F d \cos\theta$, $d$ is how far the point of application moves while the force acts. In $I = mr^2$, $r$ is the perpendicular distance from the axis. In $\lvert \vec{F}_g \rvert = G m_1 m_2 / r^2$, $r$ is the separation of two centers, and nothing is traveling at all.

Where the mark is lost. Reading $d$ in the work equation as total path length. Push a box 3.0 m forward and 3.0 m back and the total path length is 6.0 m, but the work done by a constant forward force is not $F$ times 6.0 m, because the force and the motion disagree in direction on the way back and $\cos\theta$ flips sign.

Distance divided by elapsed time gives average speed, which is why average speed and the magnitude of average velocity disagree whenever the path bends or reverses.