Science Puzzle
Why Do Your Ears Pop on a Plane?
As a plane comes in to land, your ears can start to feel blocked and sounds go muffled. Then you swallow or yawn and there's a sudden pop, and everything sounds normal again. Sucking a sweet helps, and babies are often given a bottle to drink from.
What's going on inside your ears?
The Answer
The air pressure in the cabin changes, but the pocket of air behind each eardrum stays at the old pressure until a narrow tube opens to let air in or out. When the tube opens, the pressures even out with a pop.
Behind each eardrum is a small space filled with air, the middle ear. The eardrum seals it off from the outside world, but a thin tube, the Eustachian tube, links it to the back of your throat. Most of the time that tube is squeezed shut.
A plane cruises at more than 10,000 metres, and the cabin isn't kept at ground-level pressure; it's kept at about the pressure you'd find 2,000 metres up a mountain. As the plane descends, the cabin pressure rises back towards the pressure at the ground. The air in your middle ear is still at the lower pressure, so the higher pressure outside pushes your eardrum inwards. A stretched eardrum can't vibrate freely, which is why sounds go dull, and it can hurt.
Swallowing, yawning and chewing all work muscles that briefly pull the tube open. Air rushes up into the middle ear, the pressures on each side of the eardrum even out and the eardrum springs back into place. You hear that movement as the pop. Landing is usually worse than take-off, because air escapes from the middle ear easily but has to be let back in. A cold makes it worse still, as the tube swells shut.
The principle: Equalising pressure. A difference in air pressure on either side of a thin, flexible barrier pushes it towards the lower pressure, until an opening lets air through and the pressures match.