Final answer:
The rolling frictional force decreases on a takeoff roll because the contact points between the object and the ground keep changing, resulting in a decrease in the coefficient of rolling friction.
Step-by-step explanation:
The rolling frictional force decreases on a takeoff roll because as the object rolls, the contact points between the object and the ground keep changing. Due to this change in contact points, the coefficient of rolling friction decreases, resulting in a decrease in the rolling frictional force.