For the answer to the question above, speed is a scalar quantity (meaning it can be measured using a single number that represents the amount), while velocity is composed of the scalar quantity plus the direction. As the 100-meter sprint only takes place in one direction, the speed and velocity for this are just the same. For the 400-meter sprint, however, the direction of your speed changes as you turn for her curved part of the race. Therefore, a direction change is happening.
