Which type of speed varies with time and is not constant?

Instantaneous speed refers to the speed of an object at a specific moment in time. Unlike constant speed, which does not change over time, or average speed, which is calculated over a total distance and time interval, instantaneous speed varies because it can change frequently based on the object’s movement. For example, when a car accelerates or decelerates, its instantaneous speed changes at each moment, reflecting the precise speed of the vehicle at any given point in its journey.

This concept is key in understanding motion as it provides a more detailed view of how an object moves over time, rather than just an overall rate.