Equal Speed

Equal Speed (絶対等速 (イコールスピード) ) is the ability that allows the user to make an object move at a constant speed in the direction the user wills, regardless of any force acting upon it, essentially breaking the laws of motion.

The only way for the object to stop is when the user stops it or the object breaks. The object must be whole in order for it to work.

Toaru Kagaku no Railgun
In a flashback by Shirai Kuroko, she confronts a post office robber with the power in her second year as a member of Judgment, and her first real dangerous job. The esper uses small metal spheres for his ability, making it easy to conceal and allows him to use it several times. Although, his power is slow, which gives Kuroko an advantage as she has teleportation.

The robber can apparently use his ability on an unknown amount of metal spheres, making it dangerous if thrown in large numbers. It is not shown if he can use other objects other than the spheres for his ability.