Lecturer and Coach (School Edu. Dept.) Comp. According to Newton's First Law of Motion (Law of Inertia), an object in motion will stay in motion with a constant velocity unless acted upon by an external force. In this case, the object is already sliding with a constant velocity on a frictionless horizontal table. This implies that there are no unbalanced forces acting on it in the horizontal direction. To keep it moving with the same velocity, no additional force is required, as the net force acting on it is already zero.