According to Newton's first law of motion, an object in motion will stay in motion in a straight line at a constant velocity unless acted upon by an external force. In this case, if no other forces are acting on the object, the characteristic of the moving object that would remain constant is its speed. This means that the speed of the object would remain the same without any external forces causing it to change.
For example, imagine a ball rolling on a frictionless surface with no other forces acting upon it. In this scenario, the ball would continue to move at a constant speed in a straight line due to its inertia, which is the tendency of an object to resist changes in its motion.
Therefore, in the absence of external forces, the speed of a moving object would remain constant according to Newton's first law of motion.
