Which postulate of relativity was supported by the experiments of michelson and morley

All observers measure the same speed of light,
no matter how any observer is moving.

The question is kind of awkward, though.  It seems to say that
people were having a hard time accepting this postulate of relativity,
until Michelson and Morley came along and did their experiment, and
their results gave Relativity a boost.

Actually, Michelson and Morley did their famous experiment in 1887.
At the time, Einstein was only 8 years old, and Relativity was not even
a twinkle in his eye yet.

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.