The flap won't die down.Your item headed "Silk and soap settle a century-old flap The communications protocol used by AOL Instant Messenger (AIM). FLAP runs over TCP/IP and provides the header format for transmitting IM commands and data. It includes the SNAC data type, which is the primary data structure transmitted between clients and servers. See OSCAR. 1. " (SN: 12/16/00, p. 390) prompts me to offer a less complicated answer to why flags flap. The key word is gravity. If you provide an air source blowing straight down and suspend a flag on a horizontal pole of any reasonable diameter, the flag will not flap. So why all the motion when the pole is vertical? At the free vertical edge, the upper corner has nothing to retard a gravitational grav·i·ta·tion n. 1. Physics a. The natural phenomenon of attraction between physical objects with mass or energy. b. The act or process of moving under the influence of this attraction. 2. drop--so it drops. A fold of material (several, in fact) occurs at an angle downward and away from the pole. Assuming a horizontal wind flow, the folded material presents an angled and downward sloping surface that results in a vertical and horizontal reaction. Several such folds, of course, can occur at one time, resulting in the opposite motions called "flap." I hope this helps put an end to this current flap. Richard B. Wallace Bingham Farms, Mich. One can't truly imitate im·i·tate tr.v. im·i·tat·ed, im·i·tat·ing, im·i·tates 1. To use or follow as a model. 2. a. the action of a flag in wind with a thread in soap film Noun 1. soap film - a film left on objects after they have been washed in soap film - a thin coating or layer; "the table was covered with a film of dust" , which is nearly two dimensional. Mary Hyde Berg Gloucester, Va. Lord Raleigh may have been wrong about the mechanism of asymmetry Asymmetry A lack of equivalence between two things, such as the unequal tax treatment of interest expense and dividend payments. amplification that causes flags to flutter Flutter (aeronautics) An aeroelastic self-excited vibration with a sustained or divergent amplitude, which occurs when a structure is placed in a flow of sufficiently high velocity. Flutter is an instability that can be extremely violent. in the wind, but Jun Zhang, in his experiments described in the article, omits consideration of an obvious cause because of two oversimplifications: his "flag" is one-dimensional and he hangs it vertically. An ordinary, two-dimensional flag flies horizontally in a strong wind, with two-point attachment to a vertical pole. When the wind calms, the flag droops under the force of gravity. As the wind picks up again, gravity's amplification of the inevitable small asymmetries in the system may be less obvious, but the forces are still the same and are quite sufficient to account for the flag's flap and flutter. David Bortin Whittier, Calif. Zhang and his colleagues acknowledge that gravity tugs downward on a real, three-dimensional flag and may strongly affect how and whether the flag flaps. Before trying to tackle the full, three-dimensional problem, they and other scientists have long been trying to fully explain flapping A condition in which a route in a network becomes unavailable and available over and over again. See route dampening. in a one-dimensional flag in a two-dimensional breeze. |
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