How are observation and inference different

When you see a tall, young, skinny man walking along the beach, you
observe that a tall, young, skinny man walked along the beach, and from
your observation, you know that a tall, young, skinny man walked along
the beach.

When you see a beach with nobody there, but there is a line of 5-toed
footprints in the sand along the beach, you infer that a human being
walked along the beach.  If you are a skilled anthropologist, with some
talent and experience in a few other fields whose names escape me at
the moment, you might be able to make some careful measurements of
the length, width, depth, and shape of the footprints, and then you might
be able to infer that the person who walked along the beach was a tall,
young, skinny man.  You would build all of your information from inference,
without any observations at all except for the line of footprints and your
measurements of them.

Does this your question?

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.