Answer
If the moon's speed was zero, then the gravitational force would cause the moon to move toward the earth. Since the moon is moving at a certain speed, then the gravitational force provides the centripetal acceleration to keep the moon moving in a near-circular orbit.
Work Step by Step
For an object moving in uniform circular motion with a constant speed, the centripetal force provides the precise centripetal acceleration to keep the object moving in a circle.
If the moon's speed was zero, then the gravitational force would cause the moon to move toward the earth. Since the moon is moving at a certain speed, then the gravitational force provides the centripetal acceleration to keep the moon moving in a near-circular orbit.
