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E. Linacre |
11/'97 |
Driving up (or down) a mountain leads to a reduction (or increase) of air pressure in the outer part of the ear, creating a pressure difference across the eardrum, which separates the outer ear from the middle ear. The difference distorts the eardrum, so that sounds are muffled. However, this can be cured by swallowing air and opening the Eustachian tube between the middle ear and the nasal cavity, which in turn is joined to the mouth. The air along the tube abruptly equalises pressures across the eardrum, which consequently pops back to its normal shape, quite noticeably.
The same pressure differential builds up, but more rapidly, when taking off from near sea level in a pressurised jet aircraft, because the pressure inside the cabin is held at about 780 hPa. Similarly, a large pressure variation occurs on the eardrums of scuba-divers, even when they change depth only slightly.