14 Science Bulletin, July-August 2014
spectrum (visible light). Our eardrums vibrate as sound hits them and transmits its movements to the brain into the sounds we recognize every day. Compared to many other animals, though, our ears are rudimentary. Low energy, far traveling, large frequencies as well as high energy, small frequencies escape our capabilities of hearing. Dog whistles are a perfect example of how well dogs hear high frequencies that appear silent to us. As humans get older, ears also loose quality. An example of this is how youth can hear higher frequencies than the elderly.
Another restriction of sound, bound by the laws of physics, is space. Open space is void of all mediums and therefore cannot carry sound. How, then, do astronauts communicate when working out of their shuttle? The answer to this can be explained by radio sets. When one astronaut speaks, her voice hits a sensor that works not so different from the ear:
20th U.S. edition of Gray's Anatomy of the Human Body