Definition. Constant motion refers to any type of motion when either the distance traveled by the object is the same for each second, or the speed of the object changes by the same amount each second.Imagine tapping your hand on the table once every half a second, and what that would sound like.onstant motion refers to any type of motion when either the distance traveled by the object is the same for each second, or the speed of the object changes by the same amount each second.