The direction in which a chemical reaction occurs is represented by an

In a reversible reaction, both forward and reverse directions of the reaction generally occur at the same time. While reactants are reacting to produce products, products are reacting to produce reactants. Often, a point is reached at which forward and reverse directions of the reaction occur at the same rate.

the independent variable, the one that is intentionally manipulated, is whether or not the car hits the barrier.

the dependent variable, the one that you measure the response in, is the distance that the washers travel.