Ben wants to know how a toy car's initial speed affects the distance that it is able to travel before it is stopped by friction, so he sets up the following experiment. In Ben's experiment, he places a toy car on a smooth, flat surface. Then, Ben applies varying amounts of force to the back of the car and measures the car's initial speed using a radar gun. The toy car is allowed to decelerate on its own until it stops. Finally, Ben measures the total distance that the car traveled. What is the outcome variable (dependent variable) in Ben's experiment?