How fast something is going is defined as what?

The correct definition for how fast something is going is speed. Speed is a scalar quantity that refers to the rate at which an object covers distance. It is measured as the distance traveled per unit of time, typically expressed in meters per second (m/s). Understanding speed is fundamental in physics as it describes the motion of an object without regard to its direction, focusing solely on the magnitude of velocity.

While acceleration relates to the rate of change of speed over time, it does not represent the speed itself. Distance measures how far an object has traveled but does not provide information about how quickly it is moving. Momentum, on the other hand, is a quantity that describes the motion of an object based on its mass and velocity—essentially, it is the product of speed and mass, but again does not define how fast something is going by itself.