<span>Calcium - alkali earth metals is the answer</span>
The ball is using an reaction and opposite reaction, so when you dribble a basketball you push the ball with downward force and the ground pushes the ball back up thus making the opposite reaction.
See coulomb's law. Force is inversely proportional to the distance squared. So if you multiply r by 2, the force is multiplied by (½)² = ¼.
a. F/4
