Q. Why is there a sense of pressure change inside the ear when someone goes down a mountain?

The pressure inside the middle ear is maintained equal to the external ear so to the exterior too due to a communicating duct between the pharynx and the middle ear called the auditory tube or Eustachian tube When someone goes down a mountain the air pressure upon the middle ear increases and it is necessary to do some exercises like fake swallowing to force the opening of the pharyngeal orifice of the auditory tube to equalize the pressure again.