Speed is known as the ______________________.

Speed is defined as the rate of change of displacement over time, specifically measuring how fast an object is moving regardless of its direction. It is a scalar quantity, which means it has magnitude only and does not have a direction associated with it. This differentiates speed from velocity, which is a vector quantity that includes both magnitude and direction.

In this context, the option identifying speed as a scalar quantity is the most accurate representation of its physical properties. Understanding this distinction is crucial in many engineering applications, especially when analyzing motion and forces in various systems.