when a sprinter starts running he applies force to overcome fraction and air drag. is his speed keeps going up as F=ma governs to? if he's stamina was enough to fuel him for hours will his speed will keep going up and up even though he applies a constant force until the air drag force becomes so big that his muscles' force merely counteracts the fraction plus drag and drops to zero thus reaching constant speed? What if hypothetically he runs in space on a surface which an artificial fraction made? I'm aware of the limit due to reaching speed of light and mass increase. I'm not going that far.