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 of motion states that an object will remain at rest or continue moving in a straight line at a constant velocity unless acted upon by an external force. This is often referred to as the law of inertia.
When there is no friction or air resistance, there are no external forces acting on the object to change its state of motion. Therefore, if the object is initially at rest, it will remain at rest, and if it is initially in motion, it will continue moving in a straight line with a constant velocity.
This behavior is observed in space, where the absence of significant air resistance or friction allows objects to move with very little deceleration or change in velocity over long distances. For example, once a spacecraft is set in motion, it will continue to move at a constant velocity in the absence of external forces.