Which of the following best describes speed?

Speed is defined as the distance traveled per unit of time without regard to direction. This characteristic makes speed a scalar quantity, as it is fully described by a magnitude alone. Scalars are quantities that only have size, while vectors are characterized by both magnitude and direction. Since speed does not incorporate any directional information, it is classified as a scalar.

In contrast, velocity, which is often confused with speed, is a vector quantity because it includes both speed and direction. The other options describe quantities that either do not fit neatly into the definition of speed or contain additional components that are not applicable in this context.

Thus, acknowledging that speed is solely defined by how fast an object is moving, making it a scalar, reinforces the understanding of how it differs from vector quantities which carry directional information.