Why do ears pop?
We all see our two ears visible outside as ear-pinna. Inside through the pinna traverses ear canal and it ends up into ear drum which is a thin layer that is placed tight over there. Next to the ear drum towards inside is present a space filled with air called middle ear. In nature the air in the middle ear region and the air in the ear canal should have the same pressure in everyone. This will enable us to be comfortable with our ears working properly and healthy. In order to keep the middle ear air pressure equal to that in ear canal the air is moved back and forth through the Eustachian tubes which connect middle ear and throat. This movement of air from ear to throat will equalize the air pressure inside the ear with that of outside it. This is called ear pop.
At high up in the air during flight the air up above has less pressure. When we move from ground to high in the air the high pressured air in the middle ear will be rushed through Eustachian tubes to the throat so that ear canal less pressured air equalizes with that of middle ear. So it is better for us to move our jaws while going up. But, when we are landing from a long journey in the flight to the ground the less pressured air in the middle ear should get adjusted to high pressured air in the ear canal. To make this happen forcibly or to avoid pain, people close their nose and mouth and allow the air in the lungs to reach the middle ear. This will equalize the air pressure and stop the ear popping. Due to these changes in air pressure in the ear canal the ear drum either gets blown inside or outside which causes pain to us. To avoid this pain, ear takes care of the situation by itself and rectify it. But due to excess pain we start rectifying the situation by performing certain exercises like opening the Jaw and closing the nose and mouth at appropriate situations.