Final answer:
The strength of the electrostatic force between two objects is inversely proportional to the square of the distance between them. When the distance between the objects is doubled, the force between them decreases to one fourth of the original strength.
Step-by-step explanation:
The strength of the electrostatic force between two objects is inversely proportional to the square of the distance between them. So, when the distance between the objects is doubled, the force between them decreases to one fourth of the original strength. For example, if two charged balls are initially 0.5 m apart and the distance is increased to 1 m, the strength of the electrostatic force between them will decrease to one fourth of its original value.