Final answer:
Average speed is equal to the actual speed of a body when it has uniform motion, meaning constant speed and no change in direction, because the speed is constant at all times within the period measured.
Step-by-step explanation:
The average speed of an object is defined as the total distance traveled divided by the elapsed time during which the motion occurs, without taking direction into account. When a body has uniform motion, it travels at a constant speed in a straight path, hence it does not change direction nor speed. Due to this, the average speed over any time interval is the same as the actual speed at every moment within that time interval since the speed remains unchanged throughout.
For example, if a car travels 100 kilometers over a period of 2 hours without changing speed, both the average and the actual speed of the car are 50 kilometers per hour. In this scenario, the magnitude of average velocity will also be the same as the speed because there is no change in direction. Therefore, in cases of uniform motion, the speed is consistent whether it is measured over a period of time or at any given instant.