Here's why:
* Newton's First Law of Motion (Inertia): An object at rest stays at rest, and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
* Free Space: In free space, there is no air resistance or other external forces acting on the object.
Therefore, once an object is moving at a constant velocity in free space, no additional force is needed to keep it moving at that velocity.
