Scientific American August 1993 [antikvár]

_ LETTERS TO THE EDITORSRelative AlternativesIn "Black Holes and the Centrifugal Force Paradox" [SciENTinc American, March], Marek Arwr Abramouicz proposed that dose to a black hole the cen-nifugal force acting on orbltmg objects would push them inward. A different interpretation of the phenomenon is also possible, however.hi general relativity, all energy, including kinetic energy, has weight. When an object moves faster, its weight increases. For an object orbltmg sufficiently close to a black hole, the increase in weight (force directed toward the center) more than compensates for the increase in the centrifugal force (away from the center). Consequently, the net inward force increases with the speed.Both interpretations of the physical phenomenon are equivalent, assummg that they are appropriately translated. One interpretation is probably simpler and more natural for some problems, and the other is for other probfems. hi physics, it Is almost always helpful tohave more than one way to look at the same tilings.Don N. Page Department of Physics University of Alberta EdmontonSound Reasoningi was fascinated, as I am sure many readers were, by "Listening with Two Ears," by Masakazu Konishi [Scientific American, April]. I wonder if the author can hint at the mechanism that enables me to tell if a sound source presenting sunultaneous and equal stlmuh to both of my ears is m front or in back of meor mdeed, where else it might be along the central sagittal plane?Cyril Sanger Englewood, n.j.Konishi's arUde reminded me of how our technological advances during thepast few decades were long anticipated by biological developments through evolution. The author did not comment on the owl's practice of rotating his head hi one plane. I had assumed that this motion was rdated to vision: it broadens the base of the owl's triangulation for fixing distance. Now I am curious about its use for auditory distance sensing.Joseph Burlock Poquoson, Va.Konishi replies:Confusion about whether a soimd emanates from in front or in back of a hstener occurs when the localization cues are symmetrically distributed along the central sagittal plane. For the owl, the distribution of binaural cues is complex and asymmetric, which helps in pinpointing the soimd source. Moreover, the ruff of feathers around the owl's face makes its ear more sensitive to sotmd m the front of the head than in the backmuch as the shape of the human ear helps us.Yes,this sounds like my kind of world. I'd like to apply for the AK^ Calling Card.^xnrPlease print clearly and provide allthe information requested in order to avoid any unnecessary delays.? 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MasterCard, Access, Eurocard or VISA ard is lost, stolen, expires or is terminated for any reason, or if I wish lo terminate the Authorization to bill my American Express. MasterCard, Access, Eurocardor VISAaccount. I will also notify AT&Twhenever Ichange my mailingaddress.- __* Vbu r credi t card prov klermaychargeinteresiinconformiiywiihiheiernisand cond iilonsofyouragreemeniwiihthem.mLI&T Not available in all countries. Approval or re|eciion ofihisapplkrailon is made by American Wephone and Telegraph Company in the U5.A.Insert in envelope and mail to; Aljer Global Calling Card Service, P.O. Box 258, Buffeio, NY 14226-9962, US.A.Scientific American August 1993 5