If there is no friction or air resistance acting on an object, it will continue to move at a constant velocity due to the principle of inertia and Newton's first law of motion.
Newton's first law, also known as the law of inertia, states that an object at rest will remain at rest, and an object in motion will continue moving at a constant velocity in a straight line unless acted upon by an external force.
When there is no friction or air resistance, there are no significant external forces acting on the object to change its state of motion. In the absence of these forces, the object will continue to move with the same velocity it had initially. This is because there is no force to slow it down, speed it up, or change its direction.
In such idealized conditions, the object's inertia keeps it moving at a constant velocity, as there are no forces to alter its motion. However, it's important to note that in the real world, it is nearly impossible to completely eliminate all sources of friction or air resistance, so objects rarely experience perfectly constant velocity motion over long distances.