[Marxism] RE: Noise and worker's hearts
schaffer at optonline.net
Sun Nov 27 14:17:40 MST 2005
it appears our "intelligent designer's" work is unfinished.
the ear is an amazingly sensitive organ, it enables us to hear sounds
over many many orders of magnitude in loudness. vibrations of surfaces
on the order of atomic dimensions can be detected by the ear. i used to
think the eye was tops, now i know the ear is as amazing.
being ourselves fluid on the inside surrounded by an ocean of air,
hearing organs evolved mechanisms for coupling the sound presure waves
in air effectively to the fluid in the inner ear, via three of the
smallest bones in our body. it is this exquisite impedance matching
device that gives us such sensitivity. without the impedance matching,
sound waves in air would mostly reflect back from a fluid-filled inner ear.
within the inner ear sit of order 20,000 hair cells, which respond to
induced wave motions in the fluid and convert them to electrical signals
destined for the brain. and it is here that hearing loss takes place.
prolonged exposure to loud noise can damage these hair cells, usually
permanently. someone correct me if i am wrong, but this exposure need
not be accompanied by physical pain, as in damage to the eardrum.
as Rossing points out in "The Science of Sound", we developed eyelids
for good reasons, amongst them we developed always in a sunlit
environment. Rossing points out that only in the industrial age did
humans (errr, a class of them) need to co-exist with loud machinery.
hence the comment on our dear intelligent designer, and his forgetting
to install earlids. there is also a muscular based response that can
limit the sensitivity of the ear by about 20 dB, but it is not fast
enough for gunshots and other short period bursts.
tractors: the latest reference i could find was a 1989 study of
teenagers on farm. i will keep looking. i drove tractor in the summers
for several years, but always used ear muffs.
rock concerts: my understanding is that the occasional concert induces
only temporary damage. musicians constantly on tour, however, can
experience permanent hearing loss. think levels times length of exposure.
p.s. inner ear via hair cells and fluid is also responsible for
maintaining sense of balance.
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