Težina

Težina je sila kojom gravitacijsko polje djeluje na neko tijelo mase

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. Iz definicije jakosti gravitacijskog polja, jasno je da je ta sila jednaka umnošku mase tijela i jakosti gravitacijskog polja, tj. ubrzanja sile teže. ::::

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Kako je težina sila, mjerna jedinica je, kao i za sve sile, njutn [N]. Kolokvijalno se težinu vrlo često zamjenjuje s masom, ali je to, gledajući kroz teoretski formalizam, potpuno pogrešno. category:fizika

Sila

Sila je jedan od najelementarnijih pojmova u fizici. To je vektorska veličina (određena je pravcem, smjerom i iznosom) kojom opisujemo međudjelovanje tijela i njegove okoline i kojom objašnjavamo uzroke gibanja. SI jedinica za silu je njutn čija je oznaka N (nazvana tako prema Isaacu Newtonu). Osnovna podjela sila:
- Kontaktne - kako im i samo ime govori, rezultat su fizičkog kontakta dvaju tijela. Informacija o djelovanju neke kontaktne sile se sustavom prenosi mijenjanjem međumolekulskih razmaka u strukturi materijala. Mogu djelovati koncentrirano u nekoj točki, na nekoj liniji ili na površini (kada ih se može predstaviti kao tlak). Postoji više vrsta kontaktnih sila;
- aktivne - npr. sila kojom reket udara tenisku lopticu
- reaktivne - npr. sila kojom na nas djeluje podloga na kojoj stojimo
- vanjske - sve kontaktne sile koje na neki sustav djeluju izvana
- unutarnje - sile međudjelovanja elemenata unutar nekog sustava, npr. naprezanje u materijalu
- Volumenske (masene) - vezane su uz postojanje polja sila u nekom prostoru. One ne djeluju neposredno na neki dio tijela, a na ostale dijelove posredno, već istovremeno djeluju na sve čestice tijela, tj. prožimaju ga u njegovom cijelom volumenu. U ovu vrstu sila spadaju elektromagnetske, gravitacijska, inercijalne sile. Elektromagnetske i gravitacijske sile su uvijek aktivne sile, dok su inercijalne sile svojevrsna analogija reakcijskih sila s obzirom da su reakcija na promjenu stanja gibanja. Informacija o izvoru koji stvara neko polje sila se prostorom širi brzinom svjetlosti. NAPOMENA: U biti, sve se sile mogu svesti na volumenske sile, s obzirom da su interakcije subatomskih čestica, atoma i molekula dominantno elektromagnetske prirode. Međutim, "pojednostavljenje" kontaktnom silom je dostatno, često i jedino prihvatljivo kod razmatranja konvencionalnih fizikalnih problema. Također treba napomenuti da je kod međudjelovanja čestica na molekularnoj razini (i niže) zapravo besmisleno govoriti o gravitacijskim i elektromagnetskim silama kao volumenskim silama, s obzirom da se elementarne mase i naboji mogu predstaviti točkama (nemaju volumena). Takve sile opravdavaju naziv "volumenska" tek na makrorazini. Vidi:
- Impuls sile Kategorija:Fizikalne veličine ko:힘 (물리학) simple:Force (physics)

The Lathe of Heaven

The Lathe of Heaven is a 1971 science fiction novel by Ursula K. Le Guin. It has been adapted into two television films. The novel was nominated for a Hugo Award and won the Locus Poll Award for best novel in 1972. It first appeared in the magazine Amazing Stories, before being published in paperback in 1973; a paperback edition was reprinted in New York by Eos in 1997 with ISBN 0380791854. The novel is set in Portland, Oregon at some near future time when overpopulation is a major problem. However, this is soon revealed to be only one of many future worlds that have been literally dreamed into existence by the main character, George Orr, whose subconscious mind has an inexplicable power over reality. Feeling it is not his place to change reality and wanting to gain control over his power with the goal of stopping it, George enlists the services of an ambitious psychiatrist, William Haber, who discovers this power and seeks to use it to change the world; his experiments produce a series of increasingly intolerable alternate worlds, based on an assortment of utopian and dystopian premises familiar from other science fiction works. The beginning of the chapters also feature quotes from H.G Wells. Though technology plays a slight role, the novel is largely concerned with philosophical questions about our desire to control our destiny, with Haber's positivist approach pitted against a Taoist equanimity (the title is taken from the writings of Chuang Tzu, Book XXIII, paragraph 7). Due to its portrayal of psychologically-derived alternate realities, it has often been described as Le Guin's homage to Philip K. Dick. The 1980 adaptation—generally faithful to the novel—was produced by the public television station WNET, directed by David Loxton and Fred Barzyk. It starred Bruce Davison, Kevin Conway, and Margaret Avery. Due to rights issues surrounding the use of a clip from the Beatles tune "With A Little Help From My Friends" (the tune is a intricate part to one of the novel's plot points), this version was never re-aired, and was never released to home video until 2004 (In fact, the home video release is remastered from a tape someone recorded from the original broadcast. PBS, thinking the rights issues would dog the production forever, did not have a copy of the production in their archives). The rights issue was solved by replacing the original Beatles tune with a cover version of the same song. PBS A second adaptation, retitled Lathe of Heaven, was produced for the A&E network in 2002 and directed by Philip Haas. It starred James Caan, Lukas Haas, and Lisa Bonet. This adaptation discards a significant portion of the plot, some essential characters, and much of the philosophical underpinnings of the book and the original PBS production.

External links

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- Lathe of Heaven, The Lathe of Heaven, The Lathe of Heaven, The Lathe of Heaven, The Lathe of Heaven, The Lathe of Heaven, The

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