Final answer:
The force that causes objects to stop moving on Earth when no additional force is applied is friction, which opposes the direction of motion.
Step-by-step explanation:
One of the laws of motion states, "An object in motion stays in motion unless an unbalanced force acts upon it." On Earth, the force that causes an object to eventually stop moving when no more force is being applied is friction. Friction is a force that always acts opposite to the direction of motion and is the reason objects do not continue moving indefinitely. This force is an external factor that acts on an object, thereby slowing it down or eventually stopping it. While gravity pulls objects downward, weight is the force due to gravity, and mass is the amount of matter in an object, it is friction that is responsible for halting the motion of objects on Earth when no other forces are applied to keep the object moving.