LogFAQs > #970445466

Sahuagin posted...

though this leads me to wonder how you can detect yourself falling, but I think what you can always detect are changes in acceleration, not changes in velocity. going from not falling to falling is a change in acceleration (0 to 9.8m/s/s). if you are already falling (including being thrown up into the air, and being in a full orbit), you should theoretically not feel any change even as you pass by 0 m/s (relative to the ground). (somehow I still imagine that you might feel it though; I'm not sure if that's from things like elevators and cartoons making me think you would, or if you really would. air resistance maybe would be noticeable, but you "shouldn't" feel any inertial effects.)

The vestibular system consists of two components: The semicircular canals and the otolithic organs. The semicircular canals (one for each axis of rotation) are filled with fluid and have a bundle of nerves that floats in that fluid and is fixed to the bottom of the canal. When the head rotates, the inertia of that fluid means it lags slightly behind and the bundle of nerves gets dragged through it, which the brain interprets as rotation (which triggers a number of different reflexes, such as the one that keeps your eyes fixed on something even while your head moves). If you spin a lot, then stop, the fluid will continue to spin, which creates the feeling of dizziness.

The otolithic organs each consist of a membrane that rests on top of hair cells, with tiny crystals resting on that membrane for added weight. When you move or are moved in any direction, those crystals' inertia mean they will exert more or less pressure on the hair cells, which the brain interprets as acceleration.

You're mostly correct in that it detects changes in acceleration (jerks), since what the brain perceives is the result of the inertia of those fluids/crystals causing their motion to lag slightly behind that of the rest of your body. The same thing also happens to any other fluids in the body, which is why you feel such motion in your stomach (there being quite a bit of room for your gastric juices to slosh around). You aren't going to feel constant acceleration unless there's a contact force providing it (such as accelerating in a car and having the seat push against you), so once you start falling, anything else you feel would be external forces like air resistance.