What happens to compass needles when a copper rod is placed at a 90 degree angle in the midst of them and electric current is flowing through the rod?

The electric current in the copper rod generates a magnetic field which is circular. The centres of the circles are the copper rod. The already magnetised needles will tend to become aligned with the field of the current in the rod. Presumably, the field of that current is stronger than the earth's magnetic field.

Is a  vector quantity  that refers to "the rate at which an object changes its position." imagine a person moving rapidly - one step forward and one step back - always returning to the original starting position. while this might result in a frenzy of activity, it would result in a zero velocity. because the person always returns to the original position, the motion would never result in a change in position. since velocity is defined as the rate at which the position changes, this motion results in zero velocity. if a person in motion wishes to maximize their velocity, then that person must make every effort to maximize the amount that they are displaced from their original position. every step must go into moving that person further from where he or she started. for certain, the person should never change directions and begin to return to the starting position.